Question

1. list two reasons why the temperature of a protostar increases.
2. what is the process that generates energy in the core of a main - sequence star?
3. what form of fusion occurs in a giant star?
4. what causes a nova explosion?
5. explain why only very large stars can form black holes.

Explanation:

1. As a protostar contracts due to gravity, its particles get closer and kinetic energy increases, raising temperature. Also, gravitational potential energy is converted to thermal energy.
2. In the core of a main - sequence star, hydrogen fusion (proton - proton chain or CNO cycle) occurs where hydrogen nuclei combine to form helium, releasing energy.
3. In a giant star, helium fusion occurs where helium nuclei fuse to form heavier elements like carbon and oxygen.
4. A nova explosion is caused by hydrogen fusion on the surface of a white dwarf in a binary system when hydrogen accretes from a companion star.
5. Only very large stars can form black holes because they have enough mass. After exhausting nuclear fuel, the core collapses under its own gravity. If the core mass is above the Tolman - Oppenheimer - Volkoff limit, it collapses to a black hole.

Answer:

1. Gravity - induced contraction and conversion of gravitational potential energy to thermal energy.
2. Hydrogen fusion (proton - proton chain or CNO cycle).
3. Helium fusion.
4. Hydrogen fusion on the surface of a white dwarf in a binary system.
5. They have enough mass for core collapse to form a black hole after exhausting nuclear fuel.