Question

Which event signals the birth of a star? A core shrinks and explodes in a supernova. A protostar collapses, becoming dense and hot. Extreme heat and pressure causes nuclear fusion. A mass of gas and dust grows and forms a protostar.

Answer 1

Explanation:

When the density and temperature at the core of the gravitationally collapsing nebula reaches values when nuclear fusion is triggered and sustained, that marks the birth of the star.

Answer 2

The event that signals the birth of a star is a mass of gas and dust growing and forming a protostar.

• This occurs due to a gravitational breakdown of gas and dust in a region of space. This is known as a molecular cloud. This cloud has the protostar at its center
• A protostar is a young developing star. As the molecular cloud continues to rotate while continuing to collapse, the protostar heats up and forms a disc-like shape
• Soon, the constant processes of nuclear fusion and fission lead to the release of massive quantities of energy
• The other processes mentioned in the question refer to the later stages of a star's existence

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