Question

Protostars are stars

a. that are slowly heating up and expanding.

b. that are slowly contracting and heating up.

c. whose surfaces are slowly expanding while their cores are contracting.

d. that are slowly contracting and cooling.

Answer 1

A protostar is a star that is slowly contracting and heating up. Initially cool with a large radius and low density, the protostar undergoes rapid collapse until it becomes dense and opaque enough to trap the heat released by gravitational contraction.

Step-by-step explanation:

A protostar is a star that is slowly contracting and heating up. Initially, a protostar remains fairly cool with a very large radius and a very low density. As the star shrinks, its surface area gets smaller, and so its total luminosity decreases. The protostar undergoes very rapid collapse until it becomes dense and opaque enough to trap the heat released by gravitational contraction.