One of the most intriguing of the morning press releases is now being described by Marc Seigar from the University of Arkansas, who has been trying to weigh the supermassive black holes that lurk at the centre of galaxies. Ideally, you’d do this by measuring the speed of the gas rotating around it, but that’s hard for distant galaxies.
Prof Seigar’s suggestion is to look not directly at the central gas, but – if the galaxy you’re interested in is a spiral – then you just look at the arms. His team found that the looser the arms, the smaller the black hole – and you could potentially see these features out to billions of light-years away. Compare Andromeda with the other major member (along with the Milky Way) of the local group, M33, the Triangulum Galaxy.
Andromeda has just about the tightest arms of any spiral galaxy, and a large black hole, weighing in at 180 million times the mass of the Sun. Triangulum has loose arms, and if it has a black hole at all it’s smaller than 1500 solar masses.
I have to confess I was sceptical about this release when I saw it, but the data shown during the press conference looks fairly convincing. It’s especially exciting for me as Galaxy Zoo 2 will collect information about the tightness of spiral arms among many other things, and it’s a fascinating thought to think that we might be probing the behaviour of the central black hole at the same time.
What is causing this link? It’s fair to say that they don’t know, but are blaming differences in the distribution of dark matter.