It really is amazing that we can just use Physics 101 to get the masses of entire galaxies. We just use the velocity of objects orbiting at a certain distance, and that gives us everything we need.
For your example above, we can probably easily measure the velocity of A14 (by measuring a handful of their most luminous stars). We'd have to assume a circular orbit, but that probably isn't correct. However, we *can* measure the rotation speed of the disk of Andromeda, and a circular orbit is a good assumption in that case.
3 points.
ReplyDeleteIt really is amazing that we can just use Physics 101 to get the masses of entire galaxies. We just use the velocity of objects orbiting at a certain distance, and that gives us everything we need.
For your example above, we can probably easily measure the velocity of A14 (by measuring a handful of their most luminous stars). We'd have to assume a circular orbit, but that probably isn't correct. However, we *can* measure the rotation speed of the disk of Andromeda, and a circular orbit is a good assumption in that case.