TeXes Science Practice Test

A star with a mass between 8 to 20 times that of the Sun is likely to end its life as which astronomical object?

1. A black hole

2. A white dwarf

3. A neutron star

4. A red giant

The correct answer is: A neutron star

A star with a mass between 8 to 20 times that of the Sun follows a specific evolutionary path leading to the formation of a neutron star upon its demise. These massive stars undergo nuclear fusion in their cores, creating heavier elements until iron is formed. Once iron is produced, fusion no longer generates energy; the core becomes unstable leading to a dramatic collapse. This collapse causes the outer layers of the star to explode in a supernova event. The core that remains, now incredibly dense, can form a neutron star. A neutron star is composed mostly of neutrons, with such high density that a sugar-cube-sized amount of its material would weigh about as much as a mountain on Earth. In contrast, other choices do not apply to stars of this mass range: a black hole forms from even more massive stars (greater than about 20 solar masses) where the core collapse results in an infinitely dense point. A white dwarf occurs in stars with lower mass (up to about 8 solar masses) as they shed their outer layers, while a red giant is a phase in stellar evolution rather than an end state. Thus, neutron stars are the expected remnants for the stars of the specified mass range.