In tutorial 2 we learned that black holes are formed via the death of stars more massive than 3 solar masses. So we would need to find something which is dark with a mass greater than 3 solar masses. Binary systems are the only places we can measure the mass of stars. The mass is calculated using Kepler's Third Law for two bodies orbiting a common center of mass:

M1 + M2 = (4 pi^2 a^3)/(P^2 G)

where P is the orbital period, a is the separation between the two stars and M1 and M2 are the masses of the stars.

We also have the following relationship from the common center of mass:

M2/M1 = K1/K2

where K1 and K2 are the maximum line-of-sight velocities of the two stars, also known as the radial velocities.

In order to calculate the masses of the binary stars we need to measure P, a, K1 and K2. But in the case of a binary with a black hole we can only see the visible star and so we can only measure P and K2.

Go to first page...The Mass Function