Galaxy mass refers to the total amount of matter, both in the form of stars and gas, within a galaxy. It is typically measured using various techniques, including analyzing the rotation speeds of stars and gas within the galaxy, studying the gravitational lensing effect of the galaxy on light from distant objects, and measuring the amount of dark matter present in the galaxy.
The mass of a galaxy plays a crucial role in its evolution and structure. A higher mass galaxy will have a stronger gravitational pull, which can cause it to merge with other galaxies and grow in size. The mass also affects the rate of star formation within the galaxy, with larger galaxies typically forming stars at a slower rate. Additionally, the distribution of mass within a galaxy determines its shape and structure, with spiral galaxies having a more organized distribution of mass compared to irregular galaxies.
Stellar mass refers to the total mass of all the stars within a galaxy, while gas mass refers to the total mass of gas, primarily hydrogen and helium, within a galaxy. The gas mass is typically much larger than the stellar mass, as most of the matter in a galaxy exists in the form of gas. However, the stellar mass plays a significant role in the dynamics of a galaxy, while the gas mass is essential for ongoing star formation.
The mass of a galaxy can change over time due to various factors. For example, when galaxies merge, their masses combine and increase. The addition of new stars and gas through ongoing star formation can also increase a galaxy's mass. On the other hand, the mass of a galaxy can decrease over time due to the loss of gas and stars through processes such as stellar winds and supernova explosions.
While there is no perfect method for measuring the mass of a galaxy, scientists have developed various techniques that provide accurate estimates. However, due to the presence of dark matter, which cannot be directly observed, the total mass of a galaxy may still be uncertain. As technology and scientific understanding continue to advance, our ability to accurately measure the mass of galaxies will also improve.