In fact the Milky Way is also being drawn slowly towards its nearest neighbour, the Andromeda galaxy, by gravitiational attraction, and they look set to collide – but not for 5 billion years or so! No immediate cause for alarm then. But what does a galactic pile-up actually look like?
Today's amazing high power telescopes have provided some dramatic images of colliding galaxies in various parts of the sky so we have some idea what may be awaiting our home galaxy. The Cartwheel Galaxy seen here is about 500 million light years away and is a wonderful example of a 'bull's-eye' or 'ring' galaxy – where a smaller galaxy (possibly one of the two small ones on the left of the 'wheel') has passed right through the centre of a larger one and created this stunning ring around it. The ring was caused by shock waves from the collision forcing dust and gas that was between the stars to clump together around the edge of the shock-wave 'ripple', thus creating the seeds for new star formation around the edge.
So it's particularly exciting that a couple of weeks ago a team of researchers led by Prof. Quentin Parker at the University of Hong-Kong and Prof. Albert Zijlstra at the University of Manchester announced the discovery of another 'bull's eye' galaxy, and not only that, but as mentioned above, this is the nearest one ever discovered. Named 'Kathryn's Wheel' after the wife of one of the research team, this object is also interesting because it contains far fewer stars than other known examples known - so in fact there could be a lot more of them out there, just too small for us to spot!
Kathryn's Wheel is close enough to be studied in much greater detail than has been possible before, so we look forward to finding out a lot more about these beautiful objects.
https://www.ras.org.uk/news-and-press/2699-celestial-firework-marks-nearest-galaxy-collision
http://curious.astro.cornell.edu/about-us/96-the-universe/galaxies/formation-and-evolution/530-what-happens-when-galaxies-collide-beginner
1. NASA, ESA https://www.spacetelescope.org/images/potw1036a/
2. NASA/CXC/SAO/S.Mineo et al, Optical: NASA/STScI, Infrared: NASA/JPL-Caltech http://www.space.com/27993-galaxy-collision-holiday-lights-photo.html
3. 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) https://www.spacetelescope.org/images/heic0810ae/
4. Ivan Bojicic / the scientific team https://www.ras.org.uk/images/stories/press/RAS-PR-15_51/rgb-compose3.jpg