Yet that picture is far from complete. Lying at the centre of our galaxy is a giant black hole more than 3 million times as massive as the sun. The black hole at the heart of Andromeda is believed to be 10 times the size. What will happen to these supermassive black holes during the encounter is anyone's guess.
Astronomers have recently started to find some clues, though. Most, if not all, galaxies have a supermassive black hole at their centres. Everyone thought that these hungry behemoths simply sat at the heart of their parent galaxies, vacuuming up gas clouds and ripped-apart stars. Now it seems they can go off sightseeing. A black hole can cut loose when two galaxies collide: their central supermassive black holes coalesce into a single object, and this can receive a tremendous kick in the process. Some supermassive black holes travel to the outskirts of their galaxy before returning home, others go into exile for good, catapulted unceremoniously into the lonely deep freeze of intergalactic space.
These new insights could explain some of the most puzzling observations chalked up in outer space. It's all thanks to new ways of modelling the complex distortions of space-time wrought by black holes' awesome gravitational power. Theorists have finally learned how to simulate the merger of two black holes (watch a narrated video of two galaxies merging), and the discoveries are coming thick and fast.
Labels: Cosmology