Because all the material that could rekindle it has run out - there is none left.
It may be either. Juvenile means young.
The Sun is a medium mass star in main sequence.
A protostar is the first building block of the main star. As it has not yet accumulated enough mass to join the main sequence, it will be smaller than the main star. The next stage will be a T Tauri star.
Yes.
Because all the material that could rekindle it has run out - there is none left.
High mass.
Stars don't "burn" chemically like a fire. The energy they release is obtained by fusing light elements into heavier elements. In doing that they convert mass into energy as Einstein described with the equation E=mc2. A high mass star explodes as a supernova, leaving behind a neutron star or a black hole. Neither of those is capable of nuclear fusion.
A high mass star will leave behind either a neutron star of a black hole.
High mass.
no the sun is a medium mass star.
What are the small dense remains of a high mass star
The sun is an intermediate-mass star.
the high mass star's core collapse because its gravity
It can't. A blue star is a high-mass star. A yellow star has a medium mass.
It may be either. Juvenile means young.
The Sun is a medium mass star in main sequence.