Picture of the Week 2017

20 March 2017: Some galaxies are harder to classify than others. Here, Hubble’s trusty Wide Field Camera 3 (WFC3) has captured a striking view of two interacting galaxies located some 60 million light-years away in the constellation of Leo (The Lion). The more diffuse and patchy blue glow covering the right side of the frame is known as NGC 3447 — sometimes NGC 3447B for clarity, as the name NGC 3447 can apply to the overall duo. The smaller clump to the upper left is known as NGC 3447A. The trouble with space is that it is, to state the obvious, really, really big. Astronomers have for hundreds of years been discovering and naming galaxies, stars, cosmic clouds and more. Unifying and regulating the conventions and classifications for everything ever observed is very difficult, especially when you get an ambiguous object like NGC 3447, which stubbornly defies easy categorisation. Overall, we know NGC …

13 March 2017: This image from Hubble’s Wide Field Camera 3 (WFC3) shows NGC 1448, a spiral galaxy located about 50 million light-years from Earth in the little-known constellation of Horologium (The Pendulum Clock). We tend to think of spiral galaxies as massive and roughly circular celestial bodies, so this glittering oval does not immediately appear to fit the visual bill. What’s going on? Imagine a spiral galaxy as a circular frisbee spinning gently in space. When we see it face on, our observations reveal a spectacular amount of detail and structure — a great example from Hubble is the telescope’s view of Messier 51, otherwise known as the Whirlpool Galaxy. However, the NGC 1448 frisbee is very nearly edge-on with respect to Earth, giving it an appearance that is more oval than circular. The spiral arms, which curve out from NGC 1448’s dense core, can just about be seen. Although spiral galaxies …

6 March 2017: Light travels through space at just under 300 000 kilometres per second! This staggering speed is used to calculate astronomical distances; although often misinterpreted as a unit of time (due to its misleading name), a light-year is actually a unit of astronomical distance, and is defined as the distance that light travels in a year. For reference, this is around nine trillion kilometres… but it’s a little tricky to visualise! With this in mind, 15 000 light-years may sound like a truly huge distance, but compared to the vastness of the cosmos, it’s really quite nearby. In fact, an object sitting 15 000 light-years away would not even be outside our home galaxy, the Milky Way. This is roughly the distance between us and a young super star cluster known as Westerlund 1, home to one of the largest stars ever discovered. Stars are classified according to their spectral type, …

27 February 2017: This NASA/ESA Hubble Space Telescope image showcases the remarkable galaxy UGC 12591. Classified as an S0/Sa galaxy, UGC 12591 sits somewhere between a lenticular and a spiral. It lies just under 400 million light-years away from us in the westernmost region of the Pisces–Perseus Supercluster, a long chain of galaxy clusters that stretches out for 250 million light-years — one of the largest known structures in the cosmos. The galaxy itself is also extraordinary: it is incredibly massive. The galaxy and its halo together contain several hundred billion times the mass of the Sun; four times the mass of the Milky Way. It also whirls round extremely quickly, rotating at speeds of up to 1.8 million kilometres per hour! Observations with Hubble are helping astronomers to understand the mass of UGC 1259, and to determine whether the galaxy simply formed and grew slowly over time, or whether it might have …

20 February 2017: The events surrounding the Big Bang were so cataclysmic that they left an indelible imprint on the fabric of the cosmos. We can detect these scars today by observing the oldest light in the Universe. As it was created nearly 14 billion years ago, this light — which exists now as weak microwave radiation and is thus named the cosmic microwave background (CMB) — has now expanded to permeate the entire cosmos, filling it with detectable photons. The CMB can be used to probe the cosmos via something known as the Sunyaev-Zel’dovich (SZ) effect, which was first observed over 30 years ago. We detect the CMB here on Earth when its constituent microwave photons travel to us through space. On their journey to us, they can pass through galaxy clusters that contain high-energy electrons. These electrons give the photons a tiny boost of energy. Detecting these boosted photons through our …

13 February 2017: This image was captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), a highly efficient wide-field camera covering the optical and near-infrared parts of the spectrum. While this lovely image contains hundreds of distant stars and galaxies, one vital thing is missing — the object Hubble was actually studying at the time! This is not because the target has disappeared. The ACS actually uses two detectors: the first captures the object being studied — in this case an open star cluster known as NGC 299 — while the other detector images the patch of space just ‘beneath’ it. This is what can be seen here. Technically, this picture is merely a sidekick of the actual object of interest — but space is bursting with activity, and this field of bright celestial bodies offers plenty of interest on its own. It may initially seem to show just stars, …

6 February 2017: Not to be confused with our neighbouring Andromeda Galaxy, the Andromeda constellation is one of the 88 modern constellations. More importantly for this image, it is home to the pictured NGC 7640. Many different classifications are used to identify galaxies by shape and structure — NGC 7640 is a barred spiral type. These are recognisable by their spiral arms, which fan out not from a circular core, but from an elongated bar cutting through the galaxy’s centre. Our home galaxy, the Milky Way, is also a barred spiral galaxy. NGC 7640 might not look much like a spiral in this image, but this is due to the orientation of the galaxy with respect to Earth — or to Hubble, which acted as photographer in this case! We often do not see galaxies face on, which can make features such as spiral arms less obvious. There is evidence that NGC 7640 …

30 January 2017: The Calabash Nebula, pictured here — which has the technical name OH 231.8+04.2 — is a spectacular example of the death of a low-mass star like the Sun. This image taken by the NASA/ESA Hubble Space Telescope shows the star going through a rapid transformation from a red giant to a planetary nebula, during which it blows its outer layers of gas and dust out into the surrounding space. The recently ejected material is spat out in opposite directions with immense speed — the gas shown in yellow is moving close to a million kilometres an hour. Astronomers rarely capture a star in this phase of its evolution because it occurs within the blink of an eye — in astronomical terms. Over the next thousand years the nebula is expected to evolve into a fully fledged planetary nebula. The nebula is also known as the Rotten Egg Nebula because it …

23 January 2017: The lesser-known constellation of Canes Venatici (The Hunting Dogs), is home to a variety of deep-sky objects — including this beautiful galaxy, known as NGC 4861. Astronomers are still debating on how to classify it: While its physical properties — such as mass, size and rotational velocity — indicate it to be a spiral galaxy, its appearance looks more like a comet with its dense, luminous “head” and dimmer “tail” trailing behind. Features more fitting with a dwarf irregular galaxy. Although small and messy, galaxies like NGC 4861 provide astronomers with interesting opportunities for study. Small galaxies have lower gravitational potentials, which simply means that it takes less energy to move stuff about inside them than it does in other galaxies. As a result, moving in, around, and through such a tiny galaxy is quite easy to do, making them far more likely to be suffused with streams and outflows …

16 January 2017: This stunning image, captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), shows part of the sky in the constellation of Sagittarius (The Archer). The region is rendered in exquisite detail — deep red and bright blue stars are scattered across the frame, set against a background of thousands of more distant stars and galaxies. Two features are particularly striking: the colours of the stars, and the dramatic crosses that burst from the centres of the brightest bodies. While some of the colours in this frame have been enhanced and tweaked during the process of creating the image from the observational data, different stars do indeed glow in different colours. Stars differ in colour according to their surface temperature: very hot stars are blue or white, while cooler stars are redder. They may be cooler because they are smaller, or because they are very old and have …

9 January 2017: This image taken with the Advanced Camera for Surveys (ACS) onboard the NASA/ESA Hubble Space Telescope captures a galaxy in the Virgo constellation. This camera was installed in 2002, and its wide field of view is double that of its predecessor, capturing superb images with sharp image quality and enhanced sensitivity that can be seen here. The beautiful spiral galaxy visible in the centre of the image is catchily known as RX J1140.1+0307, and it presents an interesting puzzle. At first glance, this galaxy appears to be a normal spiral galaxy, much like the Milky Way, but first appearances can be deceptive! The Milky Way galaxy, like most large galaxies, has a supermassive black hole at its centre, but some galaxies are centred on lighter, intermediate-mass black holes. RX J1140.1+0307 is such a galaxy — in fact, it is centred on one of the lowest black hole masses known in …

2 January 2017: This delicate smudge in deep space is far more turbulent than it first appears. Known as IRAS 14348-1447 — a name derived in part from that of its discoverer, the Infrared Astronomical Satellite (IRAS for short) — this celestial object is actually a combination of two gas-rich spiral galaxies. This doomed duo approached one another too closely in the past, gravity causing them to affect and tug at each other and slowly, destructively, merge into one. The image was taken by Hubble’s Advanced Camera for Surveys (ACS). IRAS 14348-1447 is located over a billion light-years away from us. It is one of the most gas-rich examples known of an ultraluminous infrared galaxy, a class of cosmic objects that shine characteristically — and incredibly — brightly in the infrared part of the spectrum. Almost 95% of the energy emitted by IRAS 14348-1447 is in the far-infrared! The huge amount of molecular …