No one.
It comes from the Greek - proto - meaning first.
So first star - a protostar.
A Protostar.
A protostar is more like a stage previous to a star - before it ignites.
A protostar takes about 100,000 years to reach the main sequence.
The term is "protostar", not "prostar". Yes. A protostar is an early stage of a star.
No. The sun was a protostar about 4.6 billion years ago.
the color of the protostar is red
Apparently someone not paying ATTENTION.
"Binary" means there are two stars. And "protostar" means the stars are in an early, or preliminary, stage.
No one
trapping of thermal energy inside the protostar
No, a protostar is basically the BEGINNING of a star's life cycle.
A protostar will live as long as 100,000 years. After material stops falling on the protostar it will enter then T Tauri star phase.