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OK I admit it. Galaxies are my favourite objects that the Hubble Space Telescope studies and images. But it’s true; there’s something so awesome about the HST images that ooze detail in a way that captures the vast and magnificent nature of these ’stellar cities’. But it’s not all about the pictures. Hubble has allowed scientists to see the farthest galaxies in the Universe, that also happen to be some of the earliest too. Those observations have given us a real insight into how the galaxies we see today form. Hubble has studied Cepheid variables in distant galaxies too, allowing us to make accurate distance measurements of far off galaxies.

Today the Hubble team have released the most stunning collection of galaxy images I have ever seen. Fifty nine images in total showing many galaxies merging. What’s fascinating is that you can piece together a rough idea of how a merger takes place, out of several images of different ‘collisions’. This isn’t unusual. Astronomers do it all the time. If you wanted to see the lifetime of a Sun-like star you obviously wouldn’t hang around for 10 billion years to watch it from start to finish. What you do is look around the Universe for different Sun-like stars at different points in their life. We can do this now to get at a very basic overview of how a galaxy merger unfolds.

The above image is made from six separate images of differing collisions. Yet put together they show the progression of a galaxy merger. In reality a galaxy collision is a slow and stately affair. In fact during galaxy mergers the stars within the galaxy generally don’t smash together. That’s because of the vast distances between stars; however some stars will ultimately be thrown from the galaxies out into the depths of space.

Over millions of years the gravity of the galaxies begins to twist and shape streams of stars. In the first panel you can see the left hand galaxy is slowly starting to deform as the two galaxies begin to interact. Emerging from the lower left of the left galaxy is a noticeable stream of stars - the first sign that a merger is underway. In the second panel the merger is further along. Here much bigger streams, called ‘tidal tails’, extend out from the galaxies as the two get ever closer. In the third panel the merger is advanced even more with a massive bridge of millions of stars stretching between the two galaxies’ cores. In the last three images the mergers show dramatic twisting and swirling shapes. As the collisions of clouds of dust and gas take place, shockwaves travel through the galaxies. This results in a staggering burst of star formation (note the young blueish stars in the fourth image). Eventually the two galaxies will become one - usually a enormous dusty elliptical galaxy.

To see the full catalogue of the Hubble merger images view the press release here and of course you can watch the latest episode of the Hubblecast about the images here.

First image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and K. Noll (STScI). Second image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University), K. Noll (STScI), and J. Westphal (Caltech). Third image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Dr. Scott Chapman from the Institute of Astronomy in Cambridge has just presented the latest results from a collaboration between the MERLIN UK radio telescope array, Keck (at optical wavelengths), the VLA in the US and the Plateau de Bure submillimetre observatory in France. The results show that there was a group of galaxies in the early Universe that experienced an incredible burst of star formation about 2 billion years after the Big Bang. This phenomenal burst of activity was observed in galaxies that were shining a mere 3 billion years after the Big Bang and is thought to have been vastly more dramatic than any star formation we see nowadays.

Remarkably it was only until relatively recently that astronomers detected a similar gathering of sub-mm galaxies in the early Universe. These galaxies are particularly faint in optical wavelengths but very bright in the radio wavelengths. Instruments like SCUBA mounted on the James Clerk Maxwell Telescope (JCMT), on Mauna Kea in Hawaii could see the sky in sub-mm wavelengths and so could detect them; allowing astronomers to investigate their nature. Yet astronomers believed that these galaxies were only part of what was going on (star-forming wise) in the early Universe, because SCUBA was good at looking at relatively cooler sub-mm galaxies.

Now, these new results from the collaboration of many telescopes do indeed show a gathering of slightly warmer galaxies, not altogether different from those spied by SCUBA, undergoing dramatic star formation. The observations indicate that these galaxies are surrounded by vast clouds of gas. That gas, the astronomers argue, will keep the star formation going at a tremendous rate for “hundreds of millions of years”.

You can see images from the results and a very cool video here.

The latest Hubblecast is now out! In this episode we present a new stunning Hubble image. M74 is a beautiful spiral galaxy located 32 million light years away. Hubble imaged the galaxy with its Advanced Camera for Surveys between 2003 and 2005.

“Messier 74, also called NGC 628, is a stunning example of a ‘grand-design’ spiral galaxy that is viewed by Earth observers nearly face-on. Its perfectly symmetrical spiral arms emanate from the central nucleus and are dotted with clusters of young blue stars. In the new Hubble image we can also see a smattering of bright pink regions decorating the spiral arms.

These are huge, relatively short-lived, clouds of hydrogen gas which glow due to the strong radiation from hot, young stars embedded within them; glowing pink regions of ionized hydrogen (hydrogen that has lost its electrons).”
You can watch the Hubblecast here.

Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration