Question

You observe a binary star system. What two quantities do you need to observe to determine the masses of the two stars?

Answer 1

Thank you for asking. Lets try to answer the question in the best way possible.

Before answering about quantities we need to observe to determine the masses of two stars. Let's first understand about binary star system. A binary star is a system of two stars having a common point or common center of mass around which the stars revolve. Often due to their distance, it appears as a single point of light however its not infact so. It usually becomes easier for the astronomers to measure the mass of stars if they are members of binary star system. For determining the mass of star, kepler's third law is applied to the stars movement around a common center. As per kepler's third law, the combined mass of two stars is directly proportional to the acceleration due to gravity. The more the acceleration due to gravity the lesser will be orbital period. So, the more combined mass of two stars, more will be acceleration due to gravity and thus lesser orbital period. The total distance between the two stars is used in Kepler's third law, to determine the combined masses of two stars in binary star system. And to determine the stars' individual masses their individual distances from the common point they orbit is used. So, from the above we can conclude that, the two quantities that we use to determine the stars' masses in the binary star system are - Average orbital distance and Orbital period.

I hope this will help you. In case if you have any problem, please feel free to ask. I'll be more than happy to help. Thanks again.