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I will be giving a talk on the Hubble Space Telescope to the Bristol Astronomical Society this Friday at 7:15pm. It’s being held at Bristol Grammar School and members of the public are welcome to come along. For more information please visit the BAS website.

For a long time the beautiful colliding galaxies known as the ‘Antennae Galaxies’, NGC 4038 and NGC 4039, (pictured above) have thought to have been somewhat unusual, a bit abnormal if you will. That’s because astronomers had thought they were between 65 to 100 million light years away. In order for them to be this distant, astronomers reasoned, their current appearance could only be explained by several strange intrinsic properties. To understand why they appeared this way, astronomers argued that they must be undergoing tremendous star formation, with super-massive clusters of stars and even hidden bright X-ray sources. But now new observations from Hubble seem to suggest that we don’t need all these unusual attributes to describe this intriguing merger.

Astronomers from the European Southern Observatory (ESO) using the Hubble Space Telescope’s Wide Field and Planetary Camera 2 have found that actually the Antennae Galaxies are closer than we thought. By observing red giant stars in the tidal tails of the colliding galaxies, the astronomers found that they are in fact about 45 million light years away. The red giant stars nearing the end of their life are good for measuring distances to galaxies; as, at certain points in their life, they have a known brightness which can make them good ’standard candles’ or distance markers. So we now know that this beautiful merging swirl confirms to our models of galaxy evolution and is in fact how we expect a galaxy merger at this distance to look.

You can read the full story here.

Top image: The Antennae Galaxies by Hubble. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgement: B. Whitmore (Space Telescope Science Institute) and James Long (ESA/Hubble).

Lower image: The tidal tail where the red giant stars were studied. Credit: NASA, ESA & Ivo Saviane (European Southern Observatory)

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)

The Hubble Space Telescope has recently found the organic molecule methane on the extrasolar planet HD 189733b. Here’s a section of the ESA press release below.

“Under the right circumstances methane can play a key role in prebiotic chemistry – the chemical reactions considered necessary to form life as we know it. Although methane has been detected on most of the planets in our Solar System, this is the first time any organic molecule has been detected on a world orbiting another star”

With an atmospheric temperature of around 900 degrees there certainly isn’t going to be life (at least as we know it) on HD 189733b. The importance of this observation is more that it is “proof that spectroscopy can eventually be done on a cooler and potentially habitable Earth-sized planet orbiting a dimmer red dwarf-type star” says Mark Swain who led the team that made the discovery at NASA’s Jet Propulsion Laboratory (JPL).

I saw this exciting news come in when I was working with the Hubble group in Germany and I began scripting a Hubblecast to cover the result. To see the finished piece visit the ESA Hubblecast no.14 page here.

Above: An artist’s impression of HD 189733b around its parent star.
Credit: Credit: ESA, NASA and G. Tinetti (University College London, UK & ESA)