They measure the mass of a black hole when that black hole is being closely orbited by another star. They look at the redshift and blueshift of the orbiting star, and measure how long it takes to orbit, and this gives enough information to tell the masses of both the black hole and the other star. It is especially accurate if they can tell what the angle is between the plane of the orbit and our line of site.
Originally posted by stpbutcool1
@Jan 18 2005, 06:36 PM
can some one tall me what they mean and if they can mesure a black hole could that make a big inpact to astronomy??
Forming opinions as we speak