Quite alot of information has been given in this tutorial so let's summarise what we have learned.

To find a black hole we need to find a dark object with a mass greater than 3 solar masses. Binary stars are the ideal place to find such an object as we can use dynamics and the laws of physics to determine the mass. We should look at X-ray binaries since we expect X-rays to be emitted when matter is being accreted onto a black hole, .

To determine the black hole mass we need the following binary parameters:

• Orbital period (P) - determined from the radial velocity curve or the light curve;
• Semi-amplitude velocity of the visible star (K2) - determined from the radial velocity curve;
• Binary inclination (i) - determined from fitting the observed light curve with models;
• Mass ratio (Q) - determined from fitting the observed light curve with models;

Once we have acquired these binary parameters we can use the mass function to calculate the mass of the compact object.

In our next tutorial we are going to apply these methods to real data, calculate the mass of the unseen object in the X-ray binary Nova Muscae 1991 and determine if it is a black hole.

In the meantime, we encourage you to play around with Binary Maker to learn more about binaries.

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