Astronomy Practice Exam

What is formed when a red giant collapses?

1. Black hole

2. Red supergiant

3. White dwarf

4. Brown dwarf

The correct answer is: White dwarf

When a red giant collapses, it can lead to the formation of a white dwarf, particularly if the progenitor star is not massive enough to undergo further collapse into a more dense object like a neutron star or black hole. A red giant is the stage in a star's life cycle where it has exhausted its hydrogen fuel in the core, causing the outer layers to expand and cool. When the core begins to collapse due to gravitational forces, it can no longer sustain nuclear fusion reactions, and the outer layers are expelled, often forming a planetary nebula. What remains is the exposed hot core, which becomes the white dwarf. The formation of a black hole typically requires a much more massive star than what becomes a red giant. A red supergiant, on the other hand, represents a later phase in more massive stars that can lead to supernovae and potentially into black holes, rather than being a result of a standard red giant collapse. A brown dwarf is a substellar object that lacks sufficient mass to initiate hydrogen fusion, and it does not emerge from the typical lifecycle of a red giant. Thus, the condition of a red giant that has shed its outer layers and retains a hot, dense core aligns perfectly with the characteristics of a