When does a protostar become a mainsequence star A When it e

When does a proto-star become a main-sequence star?

A. When it exhausts hydrogen in its core

B. When it begins to produce liquid hydrogen

C. When it becomes bright enough to see with a telescope

D. When it becomes hot enough to emit ultra-violet light

E. When it begins to fuse hydrogen into helium

Solution

When it begins to produce liquid hydrogen