What is the primary physical quantity measured using the solar mass ($M_ ext{odot}$) unit?
Stellar mass
The solar mass ($M_ ext{odot}$) serves as the fundamental standard unit for expressing the mass of stars. This unit is defined as the mass of our own Sun and is critical because stellar mass fundamentally dictates nearly every aspect of a star's evolution, including its internal burning temperature, its total lifespan, and its ultimate fate upon death. Rather than being measured directly like weighing an object on Earth, stellar mass is inferred by analyzing gravitational interactions, particularly by observing the orbital periods and distances within binary star systems and applying a modified version of Kepler's Third Law. Using $M_ ext{odot}$ allows astronomers to compare the immense heft of objects like blue giants (often over $100 ext{ M}_ ext{odot}$) against our baseline star, making these comparisons immediately meaningful.
