Question

A protostar forms when a ________ collapses under the force of gravity.

Answer 1

A protostar forms when a  NEBULA collapses under the force of gravity.

After the collapse, the young star will gather molecular cloud from its parents , which could take millions of years

hope this helps

Answer 2

Answer:

C .Nebula

Explanation:

Protostar is an early stage in the formation of a star. Main sequence star is formed after the protostar heats up to almost 10 million kelvin temperature.

The interstellar medium fills the entire space, which appears to be seemingly empty. It is comprised of gas and dust. Hydrogen is the most abundant element in this medium, which is spread across and fills the space.

Under the influence of gravity, pressure and temperature, these clouds of gas and dust come together forming nebula. Hydrogen and helium in this nebula, under high temperature  conditions form protostars.