Question

astronomers determine stellar masses by calculating them from the stars motions around the supermassive black hole at the center of the milky way. calculating them from the orbits of binary stars. calculating them from the orbital periods of unmanned probes. calculating them from the stars densities.

Explanation:

A common method for astronomers to determine stellar masses is by analyzing the orbits of binary stars. Binary - star systems follow gravitational laws, and by studying their orbital characteristics (such as orbital period, separation), the masses of the individual stars can be calculated using Newtonian mechanics and Kepler's laws. Calculating from stars' motions around the super - massive black hole is more complex and not the most common way for general stellar mass determination. Unmanned probes don't have a direct role in determining stellar masses. And while density is related to mass and volume, it's not a common direct method for determining stellar masses.

Answer:

calculating them from the orbits of binary stars.