Question

which is the final event that occurs when a star is forming? the outer layer of the star expands. gravity pulls gas and dust together. a black hole forms as the core collapses. nuclear fusion begins under high pressure.

Explanation:

The process of star - formation starts with gravity pulling gas and dust together. As the mass accumulates and the pressure and temperature in the core increase, nuclear fusion begins under high pressure. This is the defining moment when a star is born. A black - hole forms much later in the life cycle of a massive star after it has exhausted its fuel and collapses. The outer layer expanding is a later stage in the star's life as well.

Answer:

Nuclear fusion begins under high pressure.