Picture of the Week

16 September 2019: Many of the best-loved galaxies in the cosmos are remarkably large, close, massive, bright, or beautiful, often with an unusual or intriguing structure or history. However, it takes all kinds to make a Universe — as demonstrated by this Hubble Picture of the Week of Messier 110. Messier 110 may not look like much, but it is a fascinating near neighbour of our home galaxy, and an unusual example of its type. It is a member of the Local Group, a gathering of galaxies comprising the Milky Way and a number of the galaxies closest to it. Specifically, Messier 110 is one of the many satellite galaxies encircling the Andromeda Galaxy, the nearest major galaxy to our own, and is classified as a dwarf elliptical galaxy, meaning that it has a smooth and almost featureless structure. Elliptical galaxies lack arms and notable pockets of star formation — both characteristic features …

9 September 2019: This image, taken with the NASA/ESA Hubble Space Telescope, focuses on an object named UGC 695, which is located 30 million light-years away within the constellation Cetus (The Sea Monster), also known as The Whale. UGC 695 is a low-surface-brightness (LSB) galaxy. These galaxies are so faint that their brightness is less than the background brightness of Earth’s atmosphere, which makes them tricky to observe. This low brightness is the result of the relatively small number of stars within them — most of the baryonic matter in these galaxies exists in the form of huge clouds of gas and dust. The stars are also distributed over a relatively large area. LSB galaxies, like dwarf galaxies, have a high fraction of dark matter relative to the number of stars they contain. Astronomers still debate about how LSB galaxies formed in the first place.

2 September 2019: This Picture of the Week shows a dwarf galaxy named UGC 685. Such galaxies are small and contain just a tiny fraction of the number of stars in a galaxy like the Milky Way. Dwarf galaxies often show a hazy structure, an ill-defined shape, and an appearance somewhat akin to a swarm or cloud of stars — and UGC 685 is no exception to this. Classified as an SAm galaxy — a type of unbarred spiral galaxy — it is located about 15 million light-years from Earth. These data were gathered under the NASA/ESA Hubble Space Telescope’s LEGUS (Legacy ExtraGalactic UV Survey) Program, the sharpest and most comprehensive ultraviolet survey of star-forming galaxies in the nearby Universe. LEGUS is imaging 50 spiral and dwarf galaxies in our cosmic neighbourhood in multiple colours using Hubble’s Wide Field Camera 3. The survey is picking apart the structures of these galaxies and resolving …

26 August 2019: This Picture of the Week from the NASA/ESA Hubble Space Telescope shows NGC 5307, a planetary nebula which lies about 10000 light years from Earth. It can be seen in the constellation Centaurus (The Centaur), which can be seen primarily in the southern hemisphere. A planetary nebula is the final stage of a Sun-like star. As such, planetary nebulae allow us a glimpse into the future of our own Solar System. A star like our Sun will, at the end of its life, transform into a red giant. Stars are sustained by the nuclear fusion that occurs in their core, which creates energy. The nuclear fusion processes constantly try to rip the star apart. Only the gravity of the star prevents this from happening. At the end of the red giant phase of a star, these forces become unbalanced. Without enough energy created by fusion, the core of …

19 August 2019: This atmospheric Picture of the Week, taken with the NASA/ESA Hubble Space Telescope, shows a dark, gloomy scene in the constellation of Gemini (The Twins). The subject of this image confused astronomers when it was first studied — rather than being classified as a single object, it was instead recorded as two objects, owing to its symmetrical lobed structure (known as NGC 2371 and NGC 2372, though sometimes referred to together as NGC 2371/2). These two lobes are visible to the upper right and lower left of the frame, and together form something known as a planetary nebula. Despite the name, such nebulae have nothing to do with planets; NGC 2371/2 formed when a Sun-like star reached the end of its life and blasted off its outer layers, shedding the constituent material and pushing it out into space to leave just a superheated stellar remnant behind. This remnant is visible …

12 August 2019: Although it looks more like an entity seen through a microscope than a telescope, this rounded object, named NGC 2022, is certainly no alga or tiny, blobby jellyfish. Instead, it is a vast orb of gas in space, cast off by an ageing star. The star is visible in the orb's centre, shining through the gases it formerly held onto for most of its stellar life. When stars like the Sun grow advanced in age, they expand and glow red. These so-called red giants then begin to lose their outer layers of material into space. More than half of such a star's mass can be shed in this manner, forming a shell of surrounding gas. At the same time, the star's core shrinks and grows hotter, emitting ultraviolet light that causes the expelled gases to glow. This type of object is called, somewhat confusingly, a planetary nebula, though it has …

5 August 2019: The pair of strange, luminescent creatures at play in this image are actually galaxies — realms of millions upon millions of stars. This galactic duo is known as UGC 2369. The galaxies are interacting, meaning that their mutual gravitational attraction is pulling them closer and closer together and distorting their shapes in the process. A tenuous bridge of gas, dust, and stars can be seen connecting the two galaxies,, during which they pulled material out into space across the diminishing divide between them. Interaction with others is a common event in the history of most galaxies. For larger galaxies like the Milky Way, the majority of these interactions involve significantly smaller so-called dwarf galaxies. But every few aeons, a more momentous event can occur. For our home galaxy, the next big event will take place in about four billion years, when it will collide with its bigger neighbour, the Andromeda …

29 July 2019: Believe it or not, this long, luminous streak, speckled with bright blisters and pockets of material, is a spiral galaxy like our Milky Way. But how could that be? It turns out that we see this galaxy, named NGC 3432, orientated directly edge-on to us from our vantage point here on Earth. The galaxy’s spiral arms and bright core are hidden, and we instead see the thin strip of its very outer reaches. Dark bands of cosmic dust, patches of varying brightness, and pink regions of star formation help with making out the true shape of NGC 3432 — but it’s still somewhat of a challenge! Because observatories such as the NASA/ESA Hubble Space Telescope have seen spiral galaxies at every kind of orientation, astronomers can tell when we happen to have caught one from the side. The galaxy is located in the constellation of Leo Minor (The Lesser Lion). …

22 July 2019: Every now and then, the NASA/ESA Hubble Space Telescope glimpses a common object — say, a spiral galaxy — in an interesting or unusual way. A sharply angled perspective, such as the one shown in this Picture of the Week, can make it seem as if we, the viewers, are craning our necks to see over a barrier into the galaxy's bright centre. In the case of NGC 3169, this barrier is the thick dust embedded within the galaxy's spiral arms. Cosmic dust comprises a potpourri of particles, including water ice, hydrocarbons, silicates, and other solid material. It has many origins and sources, from the leftovers of star and planet formation to molecules modified over millions of years by interactions with starlight. NGC 3169 is located about 70 million light-years away in the constellation of Sextans (The Sextant). It is part of the Leo I Group of galaxies, which, like …

15 July 2019: Galaxies come in many shapes and sizes. One of the key galaxy types we see in the Universe is the spiral galaxy, as demonstrated in an especially beautiful way by the subject of this Hubble Picture of the Week, NGC 2985. NGC 2985 lies roughly over 70 million light years from the Solar System in the constellation of Ursa Major (The Great Bear). The intricate, near-perfect symmetry on display here reveals the incredible complexity of NGC 2985. Multiple tightly-wound spiral arms widen as they whorl outward from the galaxy’s bright core, slowly fading and dissipating until these majestic structures disappear into the emptiness of intergalactic space, bringing a beautiful end to their starry splendour. Over aeons, spiral galaxies tend to run into other galaxies, often resulting in mergers. These coalescing events scramble the winding structures of the original galaxies, smoothing and rounding their shape. These objects possess a beauty all …

8 July 2019: The galaxy NGC 1156 resembles a delicate cherry blossom tree flowering in springtime in this Hubble Picture of the Week. The many bright "blooms" within the galaxy are in fact stellar nurseries — regions where new stars are springing to life. Energetic light emitted by newborn stars in these regions streams outwards and encounters nearby pockets of hydrogen gas, causing it to glow with a characteristic pink hue. NGC 1156 is located in the constellation of Aries (The Ram). It is classified as a dwarf irregular galaxy, meaning that it lacks a clear spiral or rounded shape, as other galaxies have, and is on the smaller side, albeit with a relatively large central region that is more densely packed with stars. Some pockets of gas within NGC 1156 rotate in the opposite direction to the rest of the galaxy, suggesting that there has been a close encounter …

1 July 2019: This NASA/ESA Hubble Space Telescope Picture of the Week shows bright, colourful pockets of star formation blooming like roses in a spiral galaxy named NGC 972. The orange-pink glow is created as hydrogen gas reacts to the intense light streaming outwards from nearby newborn stars; these bright patches can be seen here amid dark, tangled streams of cosmic dust. Astronomers look for these telltale signs of star formation when they study galaxies throughout the cosmos, as star formation rates, locations, and histories offer critical clues as to how these colossal collections of gas and dust have evolved over time. New generations of stars contribute to — and are also, in turn, influenced by — the broader forces and factors that mould galaxies throughout the Universe, such as gravity, radiation, matter, and dark matter. German-British astronomer William Herschel is credited with the discovery of NGC 972 in 1784. Astronomers have since …

24 June 2019: This Hubble Picture of the Week shows the spiral galaxy Messier 98, which is located about 45 million light-years away in the constellation of Coma Berenices (Berenice's Hair). It was discovered in 1781 by the French astronomer Pierre Méchain, a colleague of Charles Messier, and is one of the faintest objects in Messier’s astronomical catalogue. Messier 98 is estimated to contain about a trillion of stars, and is full of cosmic dust — visible here as a web of red-brown stretching across the frame — and hydrogen gas. This abundance of star-forming material means that Messier 98 is producing stellar newborns at a high rate; the galaxy shows the characteristic signs of stars springing to life throughout its bright centre and whirling arms. This image of Messier 98 was taken in 1995 with the Wide Field and Planetary Camera 2, an instrument that was installed on the NASA/ESA …

17 June 2019: This image shows an irregular galaxy named IC 10, a member of the Local Group — a collectiongrouping of over 50 galaxies inwithin our cosmic neighbourhood that includes the Milky Way. IC 10 is a remarkable object. It is the closest-known starburst galaxy to us, meaning that it is undergoing a furious bout of star formation fueled by ample supplies of cool hydrogen gas. This gas condenses into vast molecular clouds, which then form into dense knots where pressures and temperatures reach a point sufficient to ignite nuclear fusion, thus giving rise to new generations of stars. As an irregular galaxy, IC 10 lacks the majestic shape of spiral galaxies such as the Milky Way, or the rounded, ethereal appearance of elliptical galaxies. It is a faint object, despite its relative proximity to us — justof 2.2 million light-years. In fact, IC 10 only became known to humankind in 1887, …

10 June 2019: When massive stars die at the end of their short lives, they light up the cosmos with bright, explosive bursts of light and material known as supernovae. A supernova event is incredibly energetic and intensely luminous — so much so that it forms what looks like an especially bright new star that slowly fades away over time. These exploding stars glow so incredibly brightly when they first form that they can be spotted from afar using telescopes such as the NASA/ESA Hubble Space Telescope. The subject of this image, a spiral galaxy named NGC 4051 — about 45 million light-years from Earth — has hosted multiple supernovae in past years. The first was spotted in 1983 (SN 1983I), the second in 2003 (SN 2003ie), and the most recent in 2010 (SN 2010br). These explosive events were seen scattered throughout the centre and spiral arms of NGC 4051. The SN 1983I …

3 June 2019: This striking image was taken by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3, a powerful instrument installed on the telescope in 2009. WFC3 is responsible for many of Hubble’s most breathtaking and iconic photographs, including Pictures of the Week. Shown here, NGC 7773 is a beautiful example of a barred spiral galaxy. A luminous bar-shaped structure cuts prominently through the galaxy's bright core, extending to the inner boundary of NGC 7773's sweeping, pinwheel-like spiral arms. Astronomers think that these bar structures emerge later in the lifetime of a galaxy, as star-forming material makes its way towards the galactic centre — younger spirals do not feature barred structures as often as older spirals do, suggesting that bars are a sign of galactic maturity. They are also thought to act as stellar nurseries, as they gleam brightly with copious numbers of youthful stars. Our galaxy, the Milky Way, is thought …

27 May 2019: This luminous orb is the galaxy NGC 4621, better known as Messier 59. As this latter moniker indicates, the galaxy was listed in the famous catalogue of deep-sky objects compiled by French comet-hunter Charles Messier in 1779. However, German astronomer Johann Gottfried Koehler is credited with discovering the galaxy just days before Messier added it to his collection. Modern observations show that Messier 59 is an elliptical galaxy, one of the three main kinds of galaxies along with spirals and irregulars. Ellipticals tend to be the most evolved of the trio, full of old, red stars and exhibiting little or no new star formation. Messier 59, however, bucks this trend somewhat; the galaxy does show signs of star formation, with some newborn stars residing within a disc near the core. Located in the 2000-strong Virgo Cluster of galaxies within the constellation of Virgo (The Virgin), Messier 59 lies approximately 50 …

20 May 2019: This Picture of the Week stars Messier 90, a beautiful spiral galaxy located roughly 60 million light-years from the Milky Way in the constellation of Virgo (The Virgin). The galaxy is part of the Virgo Cluster, a gathering of galaxies that is over 1200 strong. This image combines infrared, ultraviolet, and visible light gathered by the Wide Field and Planetary Camera 2 on the NASA/ESA Hubble Space Telescope. This camera was operational between 1994 and 2010, producing images with an unusual staircase-like shape as seen here. This is because the camera was made up of four light detectors with overlapping fields of view, one of which gave a higher magnification than the other three. When the four images are combined together in one picture, the high magnification image needs to be reduced in size in order for the image to align properly. This produces an image with a layout that …

13 May 2019: NGC 3384, visible in this image, has many of the features characteristic of so-called elliptical galaxies. Such galaxies glow diffusely, are rounded in shape, display few visible features, and rarely show signs of recent star formation. Instead, they are dominated by old, ageing, and red-hued stars. This stands in contrast to the sprightliness of spiral galaxies such as our home galaxy, the Milky Way, which possess significant populations of young, blue stars in spiral arms swirling around a bright core. However, NGC 3384 also displays a hint of disc-like structure towards its centre, in the form of a central ‘bar’ of stars cutting through its centre. Many spirals also boast such a bar, the Milky Way included; galactic bars are thought to funnel material through and around a galaxy’s core, helping to maintain and fuel the activities and processes occurring there. NGC 3384 is located approximately 35 million light-years away …

6 May 2019: Dotted across the sky in the constellation of Pictor (The Painter’s Easel) is the galaxy cluster highlighted here by the NASA/ESA Hubble Space Telescope: SPT-CL J0615-5746, or SPT0615 for short. First discovered by the South Pole Telescope less than a decade ago, SPT0615 is exceptional among the myriad clusters so far catalogued in our map of the Universe — it is the highest-redshift cluster for which a full, strong lens model is published. SPT0615 is a massive cluster of galaxies, one of the farthest observed to cause gravitational lensing. Gravitational lensing occurs when light from a background object is deflected around mass between the object and the observer. Among the identified background objects, there is SPT0615-JD, a galaxy that is thought to have emerged just 500 million years after the Big Bang. This puts it among the very earliest structures to form in the Universe. It is also the farthest …

29 April 2019: Few of the Universe’s residents are as iconic as the spiral galaxy. These limelight-hogging celestial objects combine whirling, pinwheeling arms with scatterings of sparkling stars, glowing bursts of gas, and dark, weaving lanes of cosmic dust, creating truly awesome scenes — especially when viewed through a telescope such as the NASA/ESA Hubble Space Telescope. In fact, this image from Hubble frames a perfect spiral specimen: the stunning NGC 2903. NGC 2903 is located about 30 million light-years away in the constellation of Leo (The Lion), and was studied as part of a Hubble survey of the central regions of roughly 145 nearby disc galaxies. This study aimed to help astronomers better understand the relationship between the black holes that lurk at the cores of galaxies like these, and the rugby-ball-shaped bulge of stars, gas, and dust at the galaxy’s centre — such as that seen in this image.

22 April 2019: This sparkling burst of stars is Messier 75. It is a globular cluster: a spherical collection of stars bound together by gravity. Clusters like this orbit around galaxies and typically reside in their outer and less-crowded areas, gathering to form dense communities in the galactic suburbs. Messier 75 lies in the constellation of Sagittarius (The Archer), around 67 000 light-years away from Earth. The majority of the cluster’s stars, about 400 000 intotal, are found in its core; it is one of the most densely populated clusters ever found, with a phenomenal luminosity of some 180 000 times that of the Sun. No wonder it photographs so well! Discovered in 1780 by Pierre Méchain, Messier 75 was also observed by Charles Messier and added to his catalogue later that year. This image of Messier 75 was captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys.

15 April 2019: Most globular clusters are almost perfectly spherical collections of stars — but Messier 62 breaks the mould. The 12-billion-year-old cluster is distorted, and stretches out on one side to form a comet-like shape with a bright head and extended tail. As one of the closest globular clusters to the centre of our galaxy, Messier 62 is likely affected by strong tidal forces that displace many of its stars, resulting in this unusual shape. When globular clusters form, they tend to be somewhat denser towards the centre. The more massive the cluster, the denser the centre is likely to be. With a mass with almost a million times that of the Sun, Messier 62 is one of the densest of them all. With so many stars at the centre, interactions and mergers occur regularly. Huge stars form and run out of fuel quickly, exploding violently and their remains collapse to form …

8 April 2019: Globular clusters are inherently beautiful objects, but the subject of this NASA/ESA Hubble Space Telescope image, Messier 3, is commonly acknowledged to be one of the most beautiful of them all. Containing an incredible half a million stars, this eight-billion-year-old cosmic bauble is one of the largest and brightest globular clusters ever discovered. However, what makes Messier 3 extra special is its unusually large population of variable stars — stars that fluctuate in brightness over time. New variable stars continue to be discovered in this sparkling stellar nest to this day, but so far we know of 274, the highest number found in any globular cluster by far. At least 170 of these are of a special variety called RR Lyrae variables, which pulse with a period directly related to their intrinsic brightness. If astronomers know how bright a star truly is based on its mass and classification, and …

1 April 2019: Star clusters are commonly featured in cosmic photoshoots, and are also well-loved by the keen eye of the NASA/ESA Hubble Space Telescope. These large gatherings of celestial gems are striking sights — and the subject of this Picture of the Week, Messier 2, is certainly no exception. Messier 2 is located in the constellation of Aquarius (The Water-Bearer), about 55 000 light-years away. It is a globular cluster, a spherical group of stars all tightly bound together by gravity. With a diameter of roughly 175 light-years, a population of 150 000 stars, and an age of 13 billion years, Messier 2 is one of the largest clusters of its kind and one of the oldest associated with the Milky Way. Most of the cluster’s mass is concentrated at its centre, with shimmering streams of stars extending outwards into space. It is bright enough that it can even be seen with …

25 March 2019: This star-studded image shows us a portion of Messier 11, an open star cluster in the southern constellation of Scutum (The Shield). Messier 11 is also known as the Wild Duck Cluster, as its brightest stars form a “V” shape that somewhat resembles a flock of ducks in flight. Messier 11 is one of the richest and most compact open clusters currently known. By investigating the brightest, hottest main sequence stars in the cluster astronomers estimate that it formed roughly 220 million years ago. Open clusters tend to contain fewer and younger stars than their more compact globular cousins, and Messier 11 is no exception: at its centre lie many blue stars, the hottest and youngest of the cluster’s few thousand stellar residents. The lifespans of open clusters are also relatively short compared to those of globular ones; stars in open clusters are spread further apart and are thus not …

18 March 2019: This fuzzy orb of light is a giant elliptical galaxy filled with an incredible 200 billion stars. Unlike spiral galaxies, which have a well-defined structure and boast picturesque spiral arms, elliptical galaxies appear fairly smooth and featureless. This is likely why this galaxy, named Messier 49, was discovered by French astronomer Charles Messier in 1771. At a distance of 56 million light-years, and measuring 157 000 light-years across, M49 was the first member of the Virgo Cluster of galaxies to be discovered, and it is more luminous than any other galaxy at its distance or nearer. Elliptical galaxies tend to contain a larger portion of older stars than spiral galaxies and also lack young blue stars. Messier 49 itself is very yellow, which indicates that the stars within it are mostly older and redder than the Sun. In fact, the last major episode of star formation was about six billion …

11 March 2019: This Hubble Picture of the Week shows Messier 28, a globular cluster in the constellation of Sagittarius (The Archer), in jewel-bright detail. It is about 18 000 light-years away from Earth. As its name suggests, this cluster belongs to the Messier catalogue of objects — however, when astronomer Charles Messier first added Messier 28 to his list in 1764, he catalogued it incorrectly, referring to it as a “[round] nebula containing no star”. While today we know nebulae to be vast, often glowing clouds of interstellar dust and ionised gases, until the early twentieth century a nebula represented any astronomical object that was not clearly localised and isolated. Any unidentified hazy light source could be called a nebula. In fact, all 110 of the astronomical objects identified by Messier were combined under the title of the Catalogue of Nebulae and Star Clusters. He classified many objects as diverse as star …

4 March 2019: Located in the constellation of Hercules, about 230 million light-years away, NGC 6052 is a pair of colliding galaxies. They were first discovered in 1784 by William Herschel and were originally classified as a single irregular galaxy because of their odd shape. However, we now know that NGC 6052 actually consists of two galaxies that are in the process of colliding. This particular image of NGC 6052 was taken using the Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope. A long time ago gravity drew the two galaxies together into the chaotic state we now observe. Stars from within both of the original galaxies now follow new trajectories caused by the new gravitational effects. However, actual collisions between stars themselves are very rare as stars are very small relative to the distances between them (most of a galaxy is empty space). Eventually things will settle down and one …

25 February 2019: Globular clusters like NGC 2419, visible in this image taken with the NASA/ESA Hubble Space Telescope, are not only beautiful, but also fascinating. They are spherical groups of stars which orbit the centre of a galaxy; in the case of NGC 2419, that galaxy is the Milky Way. NGC 2419 can be found around 300 000 light-years from the Solar System, in the constellation Lynx (the Lynx). The stars populating globular clusters are very similar to one another, with similar properties such as metallicity. The similarity of these stellar doppelgängers is due to their formation early in the history of the galaxy. As the stars in a globular cluster all formed at around the same time, they tend to display reasonably homogeneous properties. It was believed that this similarity also extended to the stellar helium content; that is, it was thought that all stars in a globular cluster would contain …

18 February 2019: Since Pluto’s status-change from fully-fledged planet to dwarf planet, Neptune holds the title of outermost planet in the Solar System. This new image of the planet was made during Hubble’s Outer Planet Atmosphere Legacy (OPAL) programme, under which it has observed the four outermost planets, including Neptune, on a yearly basis since 2014. The observations of Neptune carried out in September and November 2018 show the first evidence of a huge storm brewing, with the discovery of a new northern Great Dark Spot (visible here to the upper left of the planet’s disc, partially overlapping a large patch of white). This new dark storm is of a similar size and shape to the storm discovered in 1989 by the Voyager 2 space probe. While the future evolution of the storm will be tracked through the continued yearly Hubble observations and also by ground-based telescopes, older OPAL observations from Hubble show …

11 February 2019: One of the NASA/ESA Hubble Space Telescope’s many scientific objectives is to study the planets within the Solar System — and in past years, our system’s outer planets have been observed several times as part of Hubble’s Outer Planet Atmosphere Legacy (OPAL) programme. This programme has given us this new image of the planet Uranus, the seventh planet in the Solar System in order of increasing distance from the Sun. Past observations of Uranus using Hubble have led to many interesting insights about the cold ice giant; in 2006 the telescope managed to capture a shot in which the moon Ariel and its accompanying shadow were traversing the face of Uranus, and in 2011 Hubble was able to spot faint auroras in its atmosphere. Observations made over the course of several years also allowed astronomers to study the planet’s faint ring system as its inclination changed with respect to Earth’s …

4 February 2019: This atmospheric image shows a galaxy named Messier 85, captured in all its delicate, hazy glory by the NASA/ESA Hubble Space Telescope. Messier 85 slants through the constellation of Coma Berenices (Berenice’s Hair), and lies around 50 million light-years from Earth. It was first discovered by Charles Messier’s colleague Pierre Méchain in 1781, and is included in the Messier catalogue of celestial objects. Messier 85 is intriguing — its properties lie somewhere between those of a lenticular and an elliptical galaxy, and it appears to be interacting with two of its neighbours: the beautiful spiral NGC 4394, located out of frame to the upper left, and the small elliptical MCG 3-32-38, located out of frame to the centre bottom. The galaxy contains some 400 billion stars, most of which are very old. However, the central region hosts a population of relatively young stars of just a few billion years …

28 January 2019: This striking image combines data gathered with the Advanced Camera for Surveys, installed on the NASA/ESA Hubble Space Telescope and data from the Subaru Telescope in Hawaii. It shows just a part of the spectacular tail emerging from a spiral galaxy nicknamed D100. Tails such as these are created by a process known as ram-pressure stripping. Despite appearances, the space between galaxies in a cluster is far from empty; it is actually filled with superheated gas and plasma, which drags and pulls at galaxies as they move through it, a little like the resistance one experiences when wading through deep water. This can be strong enough to tear galaxies apart, and often results in objects with peculiar, bizarre shapes and features — as seen here. D100’s eye-catching tail of gas, which stretches far beyond this image to the left, is a particularly striking example of this phenomenon. The galaxy is …

21 January 2019: This picture showcases a gravitational lensing system called SDSS J0928+2031. Quite a few images of this type of lensing have been featured as Pictures of the Week in past months, as NASA/ESA Hubble Space Telescope data is currently being used to research how stars form and evolve in distant galaxies. Gravitational lensing can help astronomers study objects that would otherwise be too faint or appear too small for us to view. When a massive object — such as a massive cluster of galaxies, as seen here — distorts space with its immense gravitational field, it causes light from more distant galaxies to travel along altered and warped paths. It also amplifies the light, making it possible for us to observe and study its source. In this image, we see two dominant elliptical galaxies near the centre of the image. The gravity from the galaxy cluster that is the home of …

14 January 2019: This huge ball of stars — around 100 billion in total — is an elliptical galaxy located some 55 million light-years away from us. Known as Messier 89, this galaxy appears to be perfectly spherical; this is unusual for elliptical galaxies, which tend to be elongated ellipsoids. The apparently spherical nature of Messier 89 could, however, be a trick of perspective, and be caused by its orientation relative to the Earth. Messier 89 is slightly smaller than the Milky Way, but has a few interesting features that stretch far out into the surrounding space. One structure of gas and dust extends up to 150 000 light-years out from the galaxy’s centre, which is known to house a supermassive black hole. Jets of heated particles reach out to 100 000 light-years from the galaxy, suggesting that Messier 89 may have once been far more active — perhaps an active quasar or …

7 January 2019: It might appear featureless and unexciting at first glance, but NASA/ESA Hubble Space Telescope observations of this elliptical galaxy — known as Messier 105 — show that the stars near the galaxy’s centre are moving very rapidly. Astronomers have concluded that these stars are zooming around a supermassive black hole with an estimated mass of 200 million Suns! This black hole releases huge amounts of energy as it consumes matter falling into it and causing the centre to shine far brighter than its surroundings. This system is known as an active galactic nucleus. Hubble also surprised astronomers by revealing a few young stars and clusters in Messer 105, which was thought to be a “dead” galaxy incapable of star formation. Messier 105 is now thought to form roughly one Sun-like star every 10 000 years. Star-forming activity has also been spotted in a vast ring of hydrogen gas encircling both …

31 December 2018: In this image the NASA/ESA Hubble Space Telescope has captured the smoking gun of a newborn star, the Herbig–Haro objects numbered 7 to 11 (HH 7–11). These five objects, visible in blue in the top centre of the image, lie within NGC 1333, a reflection nebula full of gas and dust found about a thousand light-years away from Earth. Herbig-Haro objects like HH 7–11 are transient phenomena. Travelling away from the star that created them, at a speed of up to 250 000 kilometres per hour they disappear into nothingness within a few tens of thousands of years. The young star that is the source of HH 7-11 is called SVS 13 and all five objects are moving away from SVS 13 toward the upper left. The current distance between HH 7 and SVS 13 is about 20 000 times the distance between Earth and the Sun. Herbig–Haro objects are …

24 December 2018: This image from the NASA/ESA Hubble Space Telescope reveals an ancient, glimmering ball of stars called NGC 1466. It is a globular cluster — a gathering of stars all held together by gravity — that is slowly moving through space on the outskirts of the Large Magellanic Cloud, one of our closest galactic neighbours. NGC 1466 certainly is one for extremes. It has a mass equivalent to roughly 140 000 Suns and an age of around 13.1 billion years, making it almost as old as the Universe itself. This fossil-like relic from the early Universe lies some 160 000 light-years away from us. NGC 1466 is one of the 5 clusters in the LMC in which the level of dynamical evolution (or "dynamical age") was measured.

17 December 2018: For three weeks in October, Hubble’s eyes on the Universe closed. On the evening of Friday 5 October, the orbiting observatory put itself into safe mode after one of its gyroscopes failed. The telescope stopped making science observations, oriented its solar panels toward the Sun, and waited for further instructions from the ground. Within hours the ground control team had activated a backup gyroscope. However, when that gyroscope did not work correctly, the long, hard work to get the telescope exploring the Universe once again began in earnest. The Hubble team had either to figure out how to get this backup gyroscope working, or to turn to a previously developed and tested one-gyroscope mode, which is proven to work. It took weeks of creative thinking, repeated tests, and minor setbacks to solve the problem of the misbehaving gyroscope. Members of the Hubble operations team and of the review board suspected …

10 December 2018: This stunning spiral galaxy is Messier 100 in the constellation Coma Berenices, captured here by the NASA/ESA Hubble Space Telescope — not for the first time. Among Hubble’s most striking images of Messier 100 are a pair taken just over a month apart, before and after Servicing Mission 1, which took place 25 years ago in December 1993. After Hubble was launched, the astronomers and engineers operating the telescope found that the images it returned were fuzzy, as if it were out of focus. In fact, that was exactly what was happening. Hubble’s primary mirror functions like a satellite dish; its curved surface reflects all the light falling on it to a single focal point. However, the mirror suffered from a defect known as a spherical aberration, meaning that the light striking the edges of the mirror was not travelling to the same point as the light from the centre. …

3 December 2018: This image, from the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), reveals thousands of globular clusters lying at the core of a galaxy cluster. It was created by a Hubble survey that drew on data from three of the telescope’s separate observing programmes to explore the centre of the Coma cluster, a huge gathering of over 1000 galaxies, about 320 million light-years away, all bound together by gravity. Astronomers spotted over 22 000 globular clusters, some of which had formed a bridge connecting a pair of well-known interacting galaxies (NGC 4889 and NGC 4874). A globular cluster is a spherical group of stars that usually orbits a galaxy as a self-contained satellite. However, the globular clusters studied here are of a different type, intracluster globular clusters. Specifically, these are globular clusters that are not bound to an individual galaxy, but to a galaxy cluster — in this case, …

26 November 2018: This dark, tangled web is an object named SNR 0454-67.2. It formed in a very violent fashion — it is a supernova remnant, created after a massive star ended its life in a cataclysmic explosion and threw its constituent material out into surrounding space. This created the messy formation we see in this NASA/ESA Hubble Space Telescope image, with threads of red snaking amidst dark, turbulent clouds. SNR 0454-67.2 is situated in the Large Magellanic Cloud, a dwarf spiral galaxy that lies close to the Milky Way. The remnant is likely the result of a Type Ia supernova explosion; this category of supernovae is formed from the death of a white dwarf star, which grows and grows by siphoning material from a stellar companion until it reaches a critical mass and then explodes. As they always form via a specific mechanism — when the white dwarf hits a particular mass …

19 November 2018: Star clusters are common structures throughout the Universe, each made up of hundreds of thousands of stars all bound together by gravity. This star-filled image, taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), shows one of them: NGC 1866. NGC 1866 is found at the very edges of the Large Magellanic Cloud, a small galaxy located near to the Milky Way. The cluster was discovered in 1826 by Scottish astronomer James Dunlop, who catalogued thousands of stars and deep-sky objects during his career. However, NGC 1866 is no ordinary cluster. It is a surprisingly young globular cluster situated close enough to us that its stars can be studied individually — no mean feat given the mammoth distances involved in studying the cosmos! There is still debate over how globular clusters form, but observations such as this have revealed that most of their stars are old and …

12 November 2018: At first glance, a bright blue crescent immediately jumps out of this NASA/ESA Hubble Space Telescope image: is it a bird? A plane? Evidence of extraterrestrial life? No — it’s a galaxy. The shape of this galaxy admittedly appears to be somewhat bizarre, so confusion would be forgiven. This is due to a cosmic phenomenon called gravitational lensing. In this image, the gravitational influence of a massive galaxy cluster (called SDSS J1110+6459) is causing its surroundings spacetime to bend and warp, affecting the passage of any nearby light. This cluster to the lower left of the blue streak; a few more signs of lensing (streaks, blobs, curved lines, distorted shapes) can be seen dotted around this area. This image also features a rare and interesting type of galaxy called a jellyfish galaxy, visible just right next to the cluster and apparently dripping bright blue material. These are galaxies that lose …

5 November 2018: This captivating image from the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 shows a lonely dwarf galaxy, a staggering 100 million light-years away from Earth. This image depicts the blue compact dwarf galaxy ESO 338-4, which can be found in the constellation of Corona Australis (the Southern Crown). Blue compact dwarf galaxies take their name from the intensely blue star-forming regions that are often found within their cores. One such region can be seen embedded in ESO 338-4, which is populated with bright young stars voraciously consuming hydrogen. These massive stars are doomed to a short existence, as despite their vast supplies of hydrogen fuel. The nuclear reactions in the cores of these stars will burn through these supplies in only millions of years — a mere blink of an eye in astronomical terms. The young blue stars nestled within a cloud of dust and gas in the centre …

29 October 2018: The NASA/ESA Hubble Space Telescope doesn’t usually get much assistance from its celestial subjects — but to take this image, the telescope opted for teamwork and made good use of a fascinating cosmic phenomenon known as gravitational lensing. This effect works when the gravitational influence of a massive object, such as the galaxy cluster in the centre of this image, is so colossal that it warps the surrounding space, causing nearby light to travel along distorted paths. The massive object is effectively turned into a giant magnifying glass, bending and amplifying the light travelling from more distant galaxies lying behind it. In this particular case, astronomers used the foreground galaxy cluster (named SDSS J0915+3826) to study star formation in galaxies lying so far away that their light has taken up to 11.5 billion years to reach our eyes. These galaxies formed at a very early stage in the lifetime of …

22 October 2018: This Picture of the Week shows the unbarred spiral galaxy NGC 5033, located about 40 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The galaxy is similar in size to our own galaxy, the Milky Way, at just over 100 000 light-years across. Like in the Milky Way NGC 5033’s spiral arms are dotted with blue regions, indicating ongoing star formation. The blue patches house hot, young stars in the process of forming, while the older, cooler stars populating the galaxy’s centre cause it to appear redder in colour. In contrast to the Milky Way NGC 5033 is missing a central bar. Instead it has a bright and energetic core called an active galactic nucleus, which is powered by a supermassive black hole. This active nucleus gives it the classification of a Seyfert galaxy. Due to the ongoing activity the core of NGC 5033 shines bright …

15 October 2018: This image, taken with the NASA/ESA Hubble Space Telescope's Wide Field Camera 3 (WFC3), shows a patch of space filled with galaxies of all shapes, colours, and sizes. WFC3 is able to view many such galaxies at an unprecedented resolution — high enough to locate and study regions of star formation in a bid to understand how new stars spring to life throughout the cosmos. Stars are born within giant clouds of gas. These massive clouds, or stellar nurseries, grow unstable and begin to collapse under gravity, becoming the seeds that will grow into new stars. By analysing the luminosity, size, and formation rate of different stellar nurseries, scientists hope to learn more about the processes that can lead to the formation of a newborn star. Studying nurseries within different galaxies will provide information about star formation at different points in time and space throughout the Universe. Just below centre …

8 October 2018: This image from the NASA/ESA Hubble Space Telescope reveals a spiral galaxy named Messier 95 (also known as M95 or NGC 3351). Located about 35 million light-years away in the constellation of Leo (The Lion), this swirling spiral was discovered by astronomer Pierre Méchain in 1781, and catalogued by French astronomer Charles Messier just four days later. Messier was primarily a comet hunter, and was often left frustrated by objects in the sky that resembled comets but turned out not to be. To help other astronomers avoid confusing these objects in the future, he created his famous catalogue of Messier objects. Most definitely not a comet, Messier 95 is actually a barred spiral galaxy. The galaxy has a bar cutting through its centre, surrounded by an inner ring currently forming new stars. Also our own Milky Way is a barred spiral. As well as hosting this stellar nursery, Messier 95 …

1 October 2018: This glittering ball of stars is the globular cluster NGC 1898, which lies towards the centre of the Large Magellanic Cloud — one of our closest cosmic neighbours. The Large Magellanic Cloud is a dwarf galaxy that hosts an extremely rich population of star clusters, making it an ideal laboratory for investigating star formation. Discovered in November 1834 by British astronomer John Herschel, NGC 1898 has been scrutinised numerous times by the NASA/ESA Hubble Space Telescope. Today we know that globular clusters belong to the oldest known objects in the Universe and that they are relics of the first epochs of galaxy formation. While we already have a pretty good picture on the globular clusters of the Milky Way — still with many unanswered questions — our studies on globular clusters in nearby dwarf galaxies just started. The observations of NGC 1898 will help to determine if their properties are …

24 September 2018: This NASA/ESA Hubble Space Telescope image contains a veritable mix of different galaxies, some of which belong to the same larger structure: At the middle of the frame sits the galaxy cluster SDSS J1050+0017. The gigantic mass of this cluster creates the fascinating phenomenon of strong ravitational lensing. The gravity of the cluster bends light coming from behind it in a similar way to how the base of a wine glass bends light. The effects of this lensing can be clearly seen as curved streaks forming a circular shape around the centre of the frame. Astronomers can use these distorted galaxies to calculate the mass of the cluster — including the mass of the dark matter within it — and to peer deeper into the Universe as otherwise possible. Gravitational lensing does not only distorts the views of galaxies, it also enlarge their appearance on the sky and magnifies their …

17 September 2018: In the northern constellation of Coma Berenices (Berenice's Hair) lies the impressive Coma Cluster — a structure of over a thousand galaxies bound together by gravity. Many of these galaxies are elliptical types, as is the brighter of the two galaxies dominating this image: NGC 4860 (centre). However, the outskirts of the cluster also host younger spiral galaxies that proudly display their swirling arms. Again, this image shows a wonderful example of such a galaxy in the shape of the beautiful NGC 4858, which can be seen to the left of its bright neighbour and which stands out on account of its unusual, tangled, fiery appearance. NGC 4858 is special. Rather than being a simple spiral, it is something called a “galaxy aggregate”, which is, just as the name suggests, a central galaxy surrounded by a handful of luminous knots of material that seem to stem from it, extending and …

10 September 2018: Gravity is so much a part of our daily lives that it is all too easy to forget its awesome power — but on a galactic scale, its power becomes both strikingly clear and visually stunning. This image was taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) and shows an object named SDSS J1138+2754. It acts as a gravitational lens illustrates the true strength of gravity: A large mass — a galaxy cluster in this case — is creating such a strong gravitational field that it is bending the very fabric of its surroundings. This causes the billion-year-old light from galaxies sitting behind it to travel along distorted, curved paths, transforming the familiar shapes of spirals and ellipticals (visible in other parts of the image) into long, smudged arcs and scattered dashes. Some distant galaxies even appear multiple times in this image. Since galaxies are wide …

3 September 2018: This week’s NASA/ESA Hubble Space Telescope image showcases the galaxy NGC 4036: a lenticular galaxy some 70 million light-years away in the constellation of Ursa Major (the Great Bear). This galaxy is known for its irregular lanes of dust, which form a swirling spiral pattern around the centre of the galaxy. This core is surrounded by an extended, hazy aura of gas and dust that stretches further out into space and causes the warm, fuzzy glow that can be seen here. The centre itself is also intriguing; it is something known as a LINER-type (Low-Ionisation Nuclear Emission-line Region) galactic nucleus, meaning that it displays particular emission lines within its spectrum. The particularly bright star visible slightly to the right of the galactic centre is not within the galaxy itself; it sits between us and NGC 4036, adding a burst of brightness to the scene. Due to its relative brightness, this …

27 August 2018: Following on from last week’s Picture of the Week, this week we showcase the second part of the Hubble Deep UV (HDUV) Legacy Field, the GOODS-South view. With the addition of new ultraviolet light imagery, astronomers using the NASA/ESA Hubble Space Telescope have captured the largest panoramic view of the fire and fury of star birth in the distant Universe, encompassing 12 000 star-forming galaxies. Hubble’s ultraviolet vision opens up a new window on the evolving Universe, tracking the birth of stars over the last 11 billion years up to the cosmos’s busiest star-forming period, which happened about three billion years after the Big Bang. So far, ultraviolet light has been the missing piece of the cosmic puzzle. Now, combined with data in infrared, and visible light from Hubble and other space- and ground-based telescopes, astronomers have assembled the most comprehensive portrait yet of the Universe’s evolutionary history. The image …

20 August 2018: The Hubble Deep Field from 1995 allowed astronomers a first glimpse into the early Universe. This first picture was followed later by an even deeper observation, the Hubble Ultra Deep Field in 2004. Both images were observed in visible light, the same form of light human eyes can see. But astronomers are also interested in the many forms of invisible light out in the Universe. Therefore, the Ultra Deep Field was later observed in the infrared and the ultraviolet as well, allowing scientists to learn even more about the Universe and to look back even further into its history. It is less known that the famous deep field observations were not the only images the NASA/ESA Hubble Space Telescope took of the distant Universe. Hubble is also an essential part of the GOODS (The Great Observatories Origins Deep Survey) programme, which unites extremely deep observations from several space telescopes: NASA’s …

13 August 2018: Galaxies abound in this spectacular Hubble image; spiral arms swirl in all colours and orientations, and fuzzy ellipticals can be seen speckled across the frame as softly glowing smudges on the sky. Each visible speck of a galaxy is home to countless stars. A few stars closer to home shine brightly in the foreground, while a massive galaxy cluster nestles at the very centre of the image; an immense collection of maybe thousands of galaxies, all held together by the relentless force of gravity. Galaxy clusters are some of the most interesting objects in the cosmos. They are the nodes of the cosmic web that permeates the entire Universe — to study them is to study the organisation of matter on the grandest of scales. Not only are galaxy clusters ideal subjects for the study of dark matter and dark energy, but they also allow the study of farther-flung galaxies. …

6 August 2018: This Picture of the Week shows the colourful globular cluster NGC 2108. The cluster is nestled within the Large Magellanic Cloud, in the constellation of the Swordfish (Dorado). It was discovered in 1835 by the astronomer, mathematician, chemist and inventor John Herschel, son of the famous William Herschel. The most striking feature of this globular cluster is the gleaming ruby-red spot at the centre left of the cluster. What looks like the cluster’s watchful eye is actually a carbon star. Carbon stars are almost always cool red giants, with atmospheres containing more carbon than oxygen — the opposite to our Sun. Carbon monoxide forms in the outer layer of the star through a combination of these elements, until there is no more oxygen available. Carbon atoms are then free to form a variety of other carbon compounds, such as C2, CH, CN, C3 and SiC2, which scatter blue light within …

30 July 2018: Obtained for a research programme on star formation in old and distant galaxies, this NASA/ESA Hubble Space Telescope image obtained with its Wide Field Camera 3 (WFC3) demonstrates the immense effects of gravity; more specifically, it shows the effects of gravitational lensing caused by an object called SDSS J1152+3313. Gravitational lenses — such as this galaxy cluster SDSS J1152+3313 — possess immense masses that warp their surroundings and bend the light from faraway objects into rings, arcs, streaks, blurs, and other odd shapes. This lens, however, is not only warpping the appearance of a distant galaxy — it is also amplifying its light, making it appear much brighter than it would be without the lens. Combined with the high image quality obtainable with Hubble, this gives valuable clues into how stars formed in the early Universe. Star formation is a key process in astronomy. Everything that emits light is somehow …

23 July 2018: This image taken by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) shows a beautiful spiral galaxy called NGC 6744. At first glance, it resembles our Milky Way albeit larger, measuring more than 200 000 light-years across compared to 100 000 light-year diameter for our home galaxy. NGC 6744 is similar to our home galaxy in more ways than one. Like the Milky Way, NGC 6744 has a prominent central region packed with old yellow stars. Moving away from the galactic core, one can see parts of the dusty spiral arms painted in shades of pink and blue; while the blue sites are full of young star clusters, the pink ones are regions of active star formation, indicating that the galaxy is still very lively. In 2005, a supernova, named 2005at, was discovered within NGC 6744, adding to the argument of this galaxy’s liveliness (not visible in this …

16 July 2018: At first glance, it may seem as though this image was taken through a faulty lens, but the mind-bending distortions visible in this Hubble Wide Field Camera 3 impressive image are actually caused by a cosmic phenomenon. The bright object at the centre of the frame is the galaxy cluster SDSS J1336-0331. The enormous gravitational influence of the cluster warps the very shape and fabric of its environment (the spacetime around it) creating an effect known as strong gravitational lensing. Through this the light from background galaxies in the line of sight to the observer are bent into fantastic arcs. This effect is very useful for studying distant background galaxies. Moreover SDSS J1336-0331 is interesting in itself: the cluster was part of a study of star formation within 42 of the Brightest Cluster Galaxies (BCGs — the brightest galaxies within their host clusters, as the name would suggest). Typically located …

9 July 2018: Glowing warmly against the dark backdrop of the Universe, this image from the NASA/ESA Hubble Space Telescope shows an irregular galaxy called UGC 12682. Located approximately 70 million light-years away in the constellation of Pegasus (The Winged Horse), UGC 12682 is distorted and oddly-structured, with bright pockets of star formation. In November 2008, 14-year-old Caroline Moore from New York discovered a supernova in UGC 12682. This made her the youngest person at the time to have discovered a supernova. Follow-up observations by professional astronomers of the so-called SN 2008ha showed that it was peculiarly interesting in many different ways: its host galaxy UGC 12682 rarely produces supernovae. It is one of the faintest supernovae ever observed and after the explosion it expanded very slowly, suggesting that the explosion did not release copious amounts of energy as usually expected. Astronomers have now classified SN 2008ha as a subclass of a Type …

2 July 2018: This busy image is a treasure trove of wonders. Bright stars from the Milky Way sparkle in the foreground, the magnificent swirls of several spiral galaxies are visible across the frame, and a glowing assortment of objects at the centre make up a massive galaxy cluster. Such clusters are the biggest objects in the Universe that are held together by gravity, and can contain thousands of galaxies of all shapes and sizes. Typically, they have a mass of about one million billion times the mass of the Sun — unimaginably huge! Their incredible mass makes clusters very useful natural tools to test theories in astronomy, such as Einstein’s theory of general relativity. This tells us that objects with mass warp the fabric of spacetime around them; the more massive the object, the greater the distortion. An enormous galaxy cluster like this one therefore has a huge influence on the spacetime …

25 June 2018: This rich and dense smattering of stars is a massive globular cluster, a gravitationally-bound collection of stars that orbits the Milky Way. Globular clusters are denser and more spherical than open star clusters like the famous Pleiades. They typically contain hundreds of thousands of stars that are thought to have formed at roughly the same time. Studies have shown that this globular cluster, named NGC 6139, is home to an aging population of stars. Most globular clusters orbiting the Milky Way are estimated to be over 10 billion years old; as a result they contain some of the oldest stars in our galaxy, formed very early in the galaxy’s history. However, their role in galactic evolution is still a matter of study. This cluster is seen roughly in the direction of the centre of the Milky Way, in the constellation of Scorpius (The Scorpion). This constellation is a goldmine of …

18 June 2018: In astronomy, the devil is in the details — as this image, taken by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys and Wide-Field Camera 3, demonstrates. The numerous fuzzy blobs and glowing shapes scattered across this image make up a galaxy cluster named RXC J0949.8+1707. Located to the upper right of the frame sits an especially beautiful and interesting barred spiral galaxy, seen face-on. In the past decade, astronomers peering at this galaxy have possibly discovered not one but three examples of a cosmic phenomenon known as a supernova, the magnificently bright explosion of a star nearing the end of its life. The newest supernova candidate is nicknamed SN Antikythera, and can be seen to the lower right of the host galaxy. This shone brightly in visible and infrared light over a number of years before fading slightly. The two other supernovae, nicknamed SN Eleanor and SN Alexander, …

11 June 2018: This sparkling Picture of the Week features a massive galaxy cluster named RXC J0232.2-4420. This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters with the aim of finding the brightest distant galaxies for the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) to study. The enormous gravitational influence of such clusters distorts the space around them in such a way that they can be used as giant cosmic lenses that magnify distant background galaxies. Studying some of the earliest galaxies in the Universe will tell us more about our cosmic origins. RXC J0232.2-4420 also featured in a study that focused on galaxy clusters that are especially luminous sources of X-rays . The study searched for diffuse light around the brightest galaxies in the clusters, among the most massive …

4 June 2018: A ripple of bright blue threads through this galaxy like a misshapen lake system. The foreground of this image is littered with nearby stars with their gleaming diffraction spikes. A keen eye can also spot a few other galaxies that, while masquerading as stars at first glance, reveal their true nature on closer inspection. The central galaxy streaked with colour, IC 4870, was discovered by DeLisle Stewart in 1900 and is located approximately 28 million light-years away. It contains an active galactic nucleus, or AGN: an extremely luminous central region so alight with radiation that it can outshine the rest of the galaxy put together. AGNs emit radiation across the complete electromagnetic spectrum, from radio waves to gamma-rays, produced by the action of a central supermassive black hole that is devouring material getting too close to it. IC 4870 is also a Seyfert galaxy, a particular kind of AGN with …

28 May 2018: This NASA/ESA Hubble Space Telescope image shows a cluster of hundreds of galaxies located about 7.5 billion light-years from Earth. The brightest galaxy within this cluster named SDSS J1156+1911 and known as the Brightest Cluster Galaxy (BCG), is visible in the lower middle of the frame. It was discovered by the Sloan Giant Arcs Survey which studied data maps covering huge parts of the sky from the Sloan Digital Sky Survey: it found more than 70 galaxies that look to be significantly affected by a cosmic phenomenon known as gravitational lensing. Gravitational lensing is one of the predictions of Albert Einstein's General Theory of Relativity. The mass contained within a galaxy is so immense that it can actually warp and bend the very fabric of its surroundings (known as spacetime), forcing the light to travel along curved paths. As a result, the image of a more distant galaxy appears distorted …

21 May 2018: At first glance, this image is dominated by the vibrant glow of the swirling spiral to the lower left of the frame. However, this galaxy is far from the most interesting spectacle here — behind it sits a galaxy cluster. Galaxies are not randomly distributed in space; they swarm together, gathered up by the unyielding hand of gravity, to form groups and clusters. The Milky Way is a member of the Local Group, which is part of the Virgo Cluster, which in turn is part of the 100 000-galaxy-strong Laniakea Supercluster. The galaxy cluster seen in this image is known as SDSS J0333+0651. Clusters such as this can help astronomers understand the distant — and therefore early — Universe. SDSS J0333+0651 was imaged as part of a study of star formation in far-flung galaxies. Star-forming regions are typically not very large, stretching out for a few hundred light-years at most, …

14 May 2018: Resembling a wizard’s staff set aglow, NGC 1032 cleaves the quiet darkness of space in two in this image from the NASA/ESA Hubble Space Telescope. NGC 1032 is located about a hundred million light years away in the constellation Cetus (The Sea Monster). Although beautiful, this image perhaps does not do justice to the galaxy’s true aesthetic appeal: NGC 1032 is actually a spectacular spiral galaxy, but from Earth, the galaxy’s vast disc of gas, dust and stars is seen nearly edge-on. A handful of other galaxies can be seen lurking in the background, scattered around the narrow stripe of NGC 1032. Many are oriented face-on or at tilted angles, showing off their glamorous spiral arms and bright cores. Such orientations provide a wealth of detail about the arms and their nuclei, but fully understanding a galaxy’s three-dimensional structure also requires an edge-on view. This gives astronomers an overall idea …

7 May 2018: In the darkness of the distant Universe, galaxies resemble glowing fireflies, flickering candles, charred embers floating up from a bonfire, light bulbs softly shining. This Picture of the Week, captured by the NASA/ESA Hubble Space Telescope, shows a massive group of galaxies bound together by gravity: a cluster named RXC J0032.1+1808. This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters with the aim of finding the brightest distant galaxies for the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) to study. Expected to launch in 2018, the JWST is designed to see in infrared wavelengths, which is exceedingly useful for observing distant objects. As a result of the expansion of the Universe, very distant objects are highly redshifted (their light is shifted towards the redder end of the …

30 April 2018: Though the bright, light-speckled foreground galaxy on the left is eye-catching, it is far from the most intriguing object in this NASA/ESA Hubble Space Telescope image. In the upper part of the frame, the light from distant galaxies has been smeared and twisted into odd shapes, arcs, and streaks. This phenomenon indicates the presence of a giant galaxy cluster, which is bending the light coming from the galaxies behind it with its monstrous gravitational influence. This cluster, called SDSSJ0150+2725, lies some three billion light-years away and was first documented by the Sloan Digital Sky Survey (SDSS), hence its name. The SDSS uses a 2.5-metre optical telescope located at the Apache Point Observatory in New Mexico to observe millions of objects and create detailed 3D maps of the Universe. This particular cluster was part of the Sloan Giant Arcs Survey (SGAS), which detected galaxy clusters with strong lensing properties; their gravity …

23 April 2018: This pretty, cloud-like object may not look much like a galaxy — it lacks the well-defined arms of a spiral galaxy, or the reddish bulge of an elliptical — but it is in fact something known as a lenticular galaxy. Lenticular galaxies sit somewhere between the spiral and elliptical types; they are disc-shaped, like spirals, but they no longer form large numbers of new stars and thus contain only ageing populations of stars, like ellipticals. NGC 2655’s core is extremely luminous, resulting in its additional classification as a Seyfert galaxy: a type of active galaxy with strong and characteristic emission lines. This luminosity is thought to be produced as matter is dragged onto the accretion disc of a supermassive black hole sitting at the centre of NGC 2655. The structure of NGC 2655’s outer disc, on the other hand, appears calmer, but it is oddly-shaped. The complex dynamics of the …

16 April 2018: This intriguing image from the NASA/ESA Hubble Space Telescope shows a massive galaxy cluster called PSZ2 G138.61-10.84, about six billion light-years away. Galaxies are not randomly distributed in space, but rather aggregated in groups, clusters and superclusters. The latter span over hundreds of millions of light-years and contain billions of galaxies. Our own galaxy, for example, is part of the Local Group, which in turn is part of the giant Laniakea Supercluster. It was thanks to Hubble that we were able to study massive galactic superstructures such as the Hercules-Corona Borealis Great Wall; a giant galaxy cluster that contains billions of galaxies and extends 10 billion light-years across — making it the biggest known structure in the Universe. This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters …

9 April 2018: This NASA/ESA Hubble Space Telescope image shows a massive galaxy cluster glowing brightly in the darkness. Despite its beauty, this cluster bears the distinctly unpoetic name of PLCK_G308.3-20.2. Galaxy clusters can contain thousands of galaxies all held together by the glue of gravity. At one point in time they were believed to be the largest structures in the Universe — until they were usurped in the 1980s by the discovery of superclusters, which typically contain dozens of galaxy clusters and groups and span hundreds of millions of light-years. However, clusters do have one thing to cling on to; superclusters are not held together by gravity, so galaxy clusters still retain the title of the biggest structures in the Universe bound by gravity. One of the most interesting features of galaxy clusters is the stuff that permeates the space between the constituent galaxies: the intracluster medium (ICM). High temperatures are created …

2 April 2018: This image is packed full of galaxies! A keen eye can spot exquisite ellipticals and spectacular spirals, seen at various orientations: edge-on with the plane of the galaxy visible, face-on to show off magnificent spiral arms, and everything in between. The vast majority of these specks are galaxies, but to spot a foreground star from our own galaxy, you can look for a point of light with tell-tale diffraction spikes. The galaxies within the image are almost all part of a galaxy cluster — a monstrous collection of hundreds of galaxies all shackled together in the unyielding grip of gravity — with the charming name of SDSSJ0146-0929. The mass of this galaxy cluster is large enough to severely distort the spacetime, creating the odd, looping curves that almost encircle the central regions of the cluster. These graceful arcs are examples of a cosmic phenomenon known as an Einstein ring. The …

26 March 2018: This image, captured by the Advanced Camera for Surveys (ACS) on the NASA/ESA Hubble Space Telescope, shows the spiral galaxy NGC 5714, about 130 million light-years away in the constellation of Boötes (the Herdsman). NGC 5714 is classified as a Sc spiral galaxy, but its spiral arms — the dominating feature of spiral galaxies — are almost impossible to see, as NGC 5714 presents itself at an almost perfectly edge-on angle. Discovered by William Herschel in 1787, NGC 5714 was host to a fascinating and rare event in 2003. A faint supernova appeared about 8000 light-years below the central bulge of NGC 5714. Supernovae are the huge, violent explosions of dying stars, and the one that exploded in NGC 5714 — not visible in this much later image — was classified as a Type Ib/c supernova and named SN 2003dr. It was particularly interesting because its spectrum showed strong signatures …

19 March 2018: This idyllic scene, packed with glowing galaxies, has something truly remarkable at its core: an untouched relic of the ancient Universe. This relic can be seen in the large galaxy at the centre of the frame, a lenticular galaxy named NGC 1277. This galaxy is a member of the famous Perseus Cluster — one of the most massive objects in the known Universe, located some 220 million light-years from Earth. NGC 1277 has been dubbed a “relic of the early Universe” because all of its stars appear to have formed about 12 billion years ago. To put this in perspective, the Big Bang is thought to have happened 13.8 billion years ago. Teeming with billions of old, metal-rich stars, this galaxy is also home to many ancient globular clusters: spherical bundles of stars that orbit a galaxy like satellites. Uniquely, the globuar clusters of NGC 1277 are mostly red and …

12 March 2018: This stunning image from Hubble shows the majestic galaxy NGC 1015, found nestled within the constellation of Cetus (The Whale) 118 million light-years from Earth. In this image, we see NGC 1015 face-on, with its beautifully symmetrical swirling arms and bright central bulge creating a scene akin to a sparkling Catherine wheel firework. NGC 1015 has a bright, fairly large centre and smooth, tightly wound spiral arms and a central “bar” of gas and stars. This shape leads NGC 1015 to be classified as a barred spiral galaxy — just like our home, the Milky Way. Bars are found in around two-thirds of all spiral galaxies, and the arms of this galaxy swirl outwards from a pale yellow ring encircling the bar itself. Scientists believe that any hungry black holes lurking at the centre of barred spirals funnel gas and energy from the outer arms into the core via these …

5 March 2018: This enchanting spiral galaxy can be found in the constellation of Ursa Major (the Great Bear). Star-studded NGC 3972 lies about 65 million light-years away from the Earth, meaning that the light that we see now left it 65 million years ago, just when the dinosaurs became extinct. NGC 3972 has had its fair share of dramatic events. In 2011 astronomers observed the explosion of a type Ia supernova in the galaxy (not visible in this image). These dazzling objects all peak at the same brightness, and are brilliant enough to be seen over large distances. NGC 3972 also contains many pulsating stars called Cepheid variables. These stars change their brightness at a rate matched closely to their intrinsic luminosity, making them ideal cosmic lighthouses for measuring accurate distances to relatively nearby galaxies. Astronomers search for Cepheid variables in nearby galaxies which also contain a type Ia supernova so they …

26 February 2018: Discovered in 1900 by astronomer DeLisle Stewart and here imaged by the NASA/ESA Hubble Space Telescope, IC 4710 is an undeniably spectacular sight. The galaxy is a busy cloud of bright stars, with bright pockets — marking bursts of new star formation — scattered around its edges. IC 4710 is a dwarf irregular galaxy. As the name suggests, such galaxies are irregular and chaotic in appearance, lacking central bulges and spiral arms — they are distinctly different from spirals or ellipticals. It is thought that irregular galaxies may once have been spirals or ellipticals, but became distorted over time through external gravitational forces during interactions or mergers with other galaxies. Dwarf irregulars in particular are important to our overall understanding of galactic evolution, as they are thought to be similar to the first galaxies that formed in the Universe. IC 4710 lies roughly 25 million light-years away in the southern …

19 February 2018: Neptune, the eighth and farthest planet from the Sun, was visited for the first and last time by NASA’s Voyager 2 mission in 1989. Since then, the NASA/ESA Hubble Space Telescope has been attempting to unearth the myriad mysteries surrounding this cool, majestic behemoth — including deciphering why it has the fastest wind speeds of any planet in the Solar System, and what lies at its centre. These new Hubble images reveal one of the standout features of Neptune’s strange atmosphere: a rare dark spot, or dark vortex — a whirling high-pressure atmospheric system usually accompanied by bright “companion clouds”. This particular dark spot is named SDS-2015 (Southern Dark Spot discovered in 2015), and is only the fifth observed so far on Neptune. Although it appears to be slightly smaller than previous dark spots, observations of SDS-2015 from 2015 to 2017 revealed that the spot was once big enough to …

12 February 2018: This image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster PLCK G004.5-19.5. It was discovered by the ESA Planck satellite through the Sunyaev-Zel’dovich effect — the distortion of the cosmic microwave background radiation in the direction of the galaxy cluster, by high energy electrons in the intracluster gas. The large galaxy at the centre is the brightest galaxy in the cluster and the dominant object in this image, and above it a thin, curved gravitational lens arc is visible. This is caused by the gravitational forces of the cluster bending the light from stars and galaxies behind it, in a similar way to how a glass lens bends light. Several stars are visible in front of the cluster — recognisable by their diffraction spikes — but aside from these, all other visible objects are distant galaxies. Their light has become redshifted by the expansion of space, making them …

5 February 2018: Roughly 50 million light-years away lies a somewhat overlooked little galaxy named NGC 1559. Pictured here by Hubble’s Wide Field Camera 3, this barred spiral lies in the little-observed southern constellation of Reticulum (The Reticule). NGC 1559 has massive spiral arms chock-full of star formation, and is receding from us at a speed of about 1300 km/s. The galaxy contains the mass of around ten billion Suns — while this may sound like a lot, that is almost 100 times less massive than the Milky Way. Although NGC 1559 appears to sit near one of our nearest neighbours in the sky — the Large Magellanic Cloud (LMC), this is just a trick of perspective. In reality, NGC 1559 is physically nowhere near the LMC in space — in fact, it truly is a loner, lacking the company of any nearby galaxies or membership of any galaxy cluster. Despite its lack …

29 January 2018: This NASA/ESA Hubble Space Telescope image shows a spiral galaxy known as NGC 7331. First spotted by the prolific galaxy hunter William Herschel in 1784, NGC 7331 is located about 45 million light-years away in the constellation of Pegasus (The Winged Horse). Facing us partially edge-on, the galaxy showcases it’s beautiful arms which swirl like a whirlpool around its bright central region. Astronomers took this image using Hubble’s Wide Field Camera 3 (WFC3), as they were observing an extraordinary exploding star — a supernova — which can still be faintly seen as a tiny red dot near the galaxy’s central yellow core. Named SN2014C, it rapidly evolved from a supernova containing very little Hydrogen to one that is Hydrogen-rich — in just one year. This rarely observed metamorphosis was luminous at high energies and provides unique insight into the poorly understood final phases of massive stars. NGC 7331 is similar …

22 January 2018: This image from the NASA/ESA Hubble Space Telescope reveals a glistening and ancient globular cluster named NGC 3201 — a gathering of hundreds of thousands of stars bound together by gravity. NGC 3201 was discovered in 1826 by the Scottish astronomer James Dunlop, who described it as a “pretty large, pretty bright” object that becomes “rather irregular” towards its centre. Globular clusters are found around all large galaxies, but their origin and role in galaxy formation remain tantalisingly unclear. Astronomers recently discovered a black hole lurking at the heart of NGC 3201 — its position was revealed by the strange movements of a star being quickly flung around a massive, invisible counterpart. This sparkling group of stars also has some strange properties which make it unique amongst the over 150 globular clusters belonging to the Milky Way. NGC 3201 has an extremely fast velocity with respect to the Sun and …

15 January 2018: Researchers using a suite of telescopes including the NASA/ESA Hubble Space Telescope have spotted a supermassive black hole blowing huge bubbles of hot, bright gas — one bubble is currently expanding outwards from the black hole, while another older bubble slowly fades away. This cosmic behemoth sits within the galaxy at the bottom of this image, which lies 900 million light-years from Earth and is known as SDSS J1354+1327. The upper, larger, galaxy is known as SDSS J1354+1328. Supermassive which can have a mass equivalent to billions of suns, are found in the centre of most galaxies (including the Milky Way). These black holes are able to “feed” on their surroundings, causing them to shine brilliantly as Active Galactic Nuclei (AGN). However, this feeding process is not continuous as it depends on how much matter is available for the black hole to consume; if the surrounding material is clumpy and …

8 January 2018: In 2014, astronomers using the NASA/ESA Hubble Space Telescope found that this enormous galaxy cluster contains the mass of a staggering three million billion Suns — so it’s little wonder that it has earned the nickname of “El Gordo” (“the Fat One” in Spanish)! Known officially as ACT-CLJ0102-4915, it is the largest, hottest, and X-ray brightest galaxy cluster ever discovered in the distant Universe. Galaxy clusters are the largest objects in the Universe that are bound together by gravity. They form over billions of years as smaller groups of galaxies slowly come together. In 2012, observations from ESO’s Very Large Telescope, NASA’s Chandra X-ray Observatory and the Atacama Cosmology Telescope showed that El Gordo is actually composed of two galaxy clusters colliding at millions of kilometres per hour. The formation of galaxy clusters depends heavily on dark matter and dark energy; studying such clusters can therefore help shed light on …

1 January 2018: This image, captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), shows a galaxy named UGC 6093. As can be easily seen, UGC 6093 is something known as a barred spiral galaxy — it has beautiful arms that swirl outwards from a bar slicing through the galaxy’s centre. It is classified as an active galaxy, which means that it hosts an active galactic nucleus, or AGN: a compact region at a galaxy’s centre within which material is dragged towards a supermassive black hole. As this black hole devours the surrounding matter it emits intense radiation, causing it to shine brightly. But UGC 6093 is more exotic still. The galaxy essentially acts as a giant astronomical laser that spews out light at microwave, not visible, wavelengths — this type of object is dubbed a megamaser (maser being the term for a microwave laser). Megamasers such as UGC 6093 …

25 December 2017: This image shows something spectacular: a galaxy cluster so massive that it is warping the space around it! The cluster, whose heart is at the centre of the frame, is named RCS2 J2327, and is one of the most massive clusters known as its distance or beyond. Massive objects such as RCS2 J2327 have such a strong influence on their surroundings that they actually warp the space around them — this effect is known as gravitational lensing, and can cause light from more distant objects to be bent, distorted, and amplified, allowing us to see galaxies that would otherwise be far too distant for us to detect. Gravitational lensing is one of the predictions of Albert Einstein's General Theory of Relativity and can be observed in three different regimes: strong lensing, weak lensing, and microlensing. Unlike strong lensing, which produces stunning images of distorted galaxies, sweeping arcs, and phenomena known …

18 December 2017: It’s beginning to look a lot like Christmas in this NASA/ESA Hubble Space Telescope image of a blizzard of stars, which resembles a swirling storm in a snow globe. These stars make up the globular cluster Messier 79, located about 40 000 light-years from Earth in the constellation of Lepus (The Hare). Globular clusters are gravitationally bound groupings of up to one million stars. These giant “star globes” contain some of the oldest stars in our galaxy. Messier 79 is no exception; it contains about 150 000 stars, packed into an area measuring just roughly 120 light-years across. This 11.7-billion-year-old star cluster was first discovered by French astronomer Pierre Méchain in 1780. Méchain reported the finding to his colleague Charles Messier, who included it in his catalogue of non-cometary objects: The Messier catalogue. About four years later, using a larger telescope than Messier’s, William Herschel was able to resolve the …

11 December 2017: Galaxies glow like fireflies in this spectacular NASA/ESA Hubble Space Telescope image! This flickering swarm of cosmic fireflies is a rich cluster of galaxies called Abell 2163. Abell 2163 is a member of the Abell catalogue, an all-sky catalogue of over 4000 galaxy clusters. It is particularly well-studied because the material sitting at its core (its intracluster medium) exhibits exceptional properties, including a large and bright radio halo and extraordinarily high temperatures and X-ray luminosities. It is the hottest cluster in the catalogue! Observing massive clusters like Abell 2163 can contribute to the study of dark matter, and provide a new perspective on the distant Universe via phenomena such as gravitational lensing. This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3, partially for an extensive observing programme called RELICS. The programme is imaging 41 massive galaxy clusters to find the brightest distant galaxies, which will …

4 December 2017: Don’t be fooled! The subject of this Picture of the Week, ESO 580-49, may seem tranquil and unassuming, but this spiral galaxy actually displays some explosive tendencies. In October of 2011, a cataclysmic burst of high-energy gamma-ray radiation — known as a gamma-ray burst, or GRB — was detected coming from the region of sky containing ESO 580-49. Astronomers believe that the galaxy was the host of the GRB, given that the chance of a coincidental alignment between the two is roughly 1 in 10 million. At a distance of around 185 million light-years from Earth, it was the second-closest gamma-ray burst (GRB) ever detected. Gamma-ray bursts are among the brightest events in the cosmos, occasionally outshining the combined gamma-ray output of the entire observable Universe for a few seconds. The exact cause of the GRB that probably occurred within this galaxy, catalogued as GRB 111005A, remains a mystery. Several …

27 November 2017: This picturesque view from the NASA/ESA Hubble Space Telescope peers into the distant Universe to reveal a galaxy cluster called Abell 2537. Galaxy clusters such as this one contain thousands of galaxies of all ages, shapes and sizes, together totalling a mass thousands of times greater than that of the Milky Way. These groupings of galaxies are colossal — they are the largest structures in the Universe to be held together by their own gravity. Clusters are useful in probing mysterious cosmic phenomena like dark matter and dark energy, the latter of which is thought to define the geometry of the entire Universe. There is so much matter stuffed into a cluster like Abell 2537 that its gravity has visible effects on its surroundings. Abell 2537’s gravity warps the very structure of its environment (spacetime), causing light to travel along distorted paths through space. This phenomenon can produce a magnifying …

20 November 2017: This NASA/ESA Hubble Space Telescope image reveals the Cosmic Snake, a distant galaxy peppered with clumpy regions of intense star formation that appear warped by the effect of gravitational lensing. This giant arc-like galaxy is actually behind the huge galaxy cluster MACSJ1206.2-0847, but thanks to the cluster’s gravity, we can see it from Earth. Light from the distant, high-redshift galaxy arrives at Earth, having been distorted by the gigantic gravitational influence of the intervening cluster. Fascinatingly, instead of making it more difficult to perceive cosmological objects, such strong lensing effects improve the resolution and depth of an image by magnifying the background object. Sometimes gravitational lensing can even produce multiple images of the object as light is bent in different directions around the foreground cluster. Using Hubble, astronomers recently looked at several such images of the Cosmic Snake, each with a different level of magnification. Using this technique, the galaxy …

13 November 2017: This new Picture of the Week, taken by the NASA/ESA Hubble Space Telescope, shows the dwarf galaxy NGC 4625, located about 30 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The image, acquired with the Advanced Camera for Surveys (ACS), reveals the single spiral arm of the galaxy, which gives it an asymmetric appearance. But why is there only one spiral arm, when spiral galaxies normally have at least two? Astronomers looked at NGC 4625 in different wavelengths in the hope of solving this cosmic mystery. Observations in the ultraviolet provided the first hint: in ultraviolet light the disc of the galaxy appears four times larger than on the image depicted here. An indication that there are a large number of very young and hot — hence mainly visible in the ultraviolet — stars forming in the outer regions of the galaxy. These young stars are …

6 November 2017: This NASA/ESA Hubble Space Telescope image seems to sink into the screen, plunging the viewer into the dark depths of the early Universe. Massive galaxy clusters — such as the subject of this image, Abell 1300 — help us to better understand the cosmos. They are essentially giant natural telescopes, magnifying the light from any galaxies sitting behind them and helping us peer further back in time. This bizarre kind of time travel is possible due to a phenomenon called gravitational lensing, whereby the gravitational influence of a massive object such as Abell 1300 acts like a lens, bending the very fabric of space around it and thus causing more distant light to move in a curved path. To the observer, the source of the light — a background object such as a primordial galaxy, for example — appears both distorted and magnified. The lensing power of massive clusters has …

30 October 2017: The Universe contains some truly massive objects. Although we are still unsure how such gigantic things come to be, the current leading theory is known as hierarchical clustering, whereby small clumps of matter collide and merge to grow ever larger. The 14-billion-year history of the Universe has seen the formation of some enormous cosmic structures, including galaxy groups, clusters, and superclusters — the largest known structures in the cosmos! This particular cluster is called Abell 665. It was named after its discoverer, George O. Abell, who included it in his seminal 1958 cluster catalogue. Abell 665 is located in the well-known northern constellation of Ursa Major (The Great Bear). This incredible image combines visible and infrared light gathered by the NASA/ESA Hubble Space Telescope using two of its cameras: the Advanced Camera for Surveys and the Wide Field Camera 3. Abell 665 is the only galaxy cluster in Abell’s entire …

23 October 2017: This NASA/ESA Hubble Space Telescope image is chock-full of galaxies — each glowing speck is a different galaxy, bar the bright flash in the middle of the image which is actually a star lying within our own galaxy that just happened to be in the way. At the centre of the image lies something especially interesting, the centre of the massive galaxy cluster called WHL J24.3324-8.477, including the brightest galaxy of the cluster. The Universe contains structures on various scales — planets collect around stars, stars collect into galaxies, galaxies collect into groups, and galaxy groups collect into clusters. Galaxy clusters contain hundreds to thousands of galaxies bound together by gravity. Dark matter and dark energy play key roles in the formation and evolution of these clusters, so studying massive galaxy clusters can help scientists to unravel the mysteries of these elusive phenomena. This infrared image was taken by Hubble’s …