Galaxy light show

This Hubble Picture of the week features NGC 1672, a barred spiral galaxy located 49 million light-years from Earth in the constellation Dorado. This galaxy is a multi-talented light show, showing off an impressive array of different celestial lights. Like any spiral galaxy, its disc is filled with billions of shining stars that give it a beautiful glow. Along its two large arms, bubbles of hydrogen gas are made to shine a striking red light by the powerful radiation of newly-forming stars within. Near to the centre lie some particularly spectacular stars; newly-formed and extremely hot, they are embedded in a ring of hot gas and are emitting powerful X-rays. And in the very centre sits an even more brilliant source of X-rays, an active galactic nucleus created by the heated accretion disc around NGC 1672’s supermassive black hole; this makes NGC 1672 a Seyfert galaxy.

But a highlight of this image is the most fleeting and temporary of these lights: supernova SN 2017GAX. This was a Type I supernova caused by the core-collapse and subsequent explosion of a giant star, going from invisibility to a new light in the sky in just a matter of days. The two images of NGC 1672 here show two views of the galaxy; the one on the right includes Hubble data from that year which captures the supernova as it comes to the end of its lifespan. Look for it as a small green dot, just below the crook of the spiral arm on the right side. If you can't find it, try looking at this collage.

If you look very closely between the left and right images in this comparison, you might also notice the larger stars in the bottom-left quadrant seem to shift position a little, even though the galaxy and smaller stars don’t move. That’s because the Hubble data which shows the supernova was obtained twelve years after most of the rest of the data in this image! The stars you see moving lie between Earth and NGC 1672, most likely in the Milky Way galaxy, which is close enough that over twelve years’ time we can notice their motion relative to us.

[Image Description: A spiral galaxy with an oval-shaped disc. Two large arms curve out away from the ends of the disc. The arms are traced by bright pink patches where stars are forming and by dark reddish threads of dust. The core is very bright and star-filled. Some large stars appear in front of the galaxy.]