Star

Mass is the most important stellar property. This is because a star's life is a continuous fight against gravity, and gravity is directly related to mass. The more massive a star is, the stronger its gravity. Mass therefore determines how strong the gravitational force is at every point within the star. This in turn dictates how fast the star has to consume its fuel to keep its gas hot enough to maintain hydrostatic equilibrium everywhere inside it. This controls the temperature structure of the star and the methods by which energy is transported from the core to the surface. It even controls the star's lifetime, since the rate of fuel consumption determines lifetime.

The smallest stars are about 0.08 times the mass of the Sun. If a ball of gas is any smaller than that, it cannot raise its internal temperature high enough while it is Figure 3. Pulsating stars produce a light curve like this one, compiled from the variable star Mira during 1964-65. Illustration by Hans & Cassidy. Courtesy of Gale Group. forming to ignite the necessary fusion reactions in its core. The largest stars are about 50 times more massive than the Sun. A star more massive than that would shine so intensely that its radiation would start to overcome gravity—the star would shed mass from its surface so quickly that it could never be stable. Virtually everything about a star is related to its mass, and in the next section, we will see how this works in four case histories.