The luminosity of a galaxy is directly proportional to its mass. This means that the more luminous a galaxy is, the more massive it is likely to be. This relationship is known as the luminosity-mass relationship.
Scientists use the luminosity-mass relationship to estimate a galaxy's mass from its luminosity. This is done by comparing the galaxy's luminosity to that of other galaxies with known masses.
Knowing a galaxy's mass is important because it can tell us about the galaxy's evolution, structure, and dynamics. It can also help us understand how galaxies form and how they interact with each other.
While the luminosity-mass relationship provides a good estimate of a galaxy's mass, it is not always accurate. Other factors such as the age and composition of stars in the galaxy can also affect its luminosity and therefore, its estimated mass.
Yes, there are other methods for determining a galaxy's mass, such as measuring the rotation curves or using gravitational lensing. These methods provide more direct measurements of a galaxy's mass, but they also have their limitations and may not be applicable to all galaxies.