Question

What happens to the mass of a star which collapses into a black hole?

Answer 1

The mass remains same.

Explanation:

Its density increases millions of times as the star collapse due to gr aviation..As mass remain same but the size reduce its surface gravity will be very great as distance to center is reduced.

Answer 2

Mass/energy is always conserved.

Explanation:

First of all, when a star collapses into a black hole, it is not the whole star which collapses. Only the stellar core has the density required to become a black hole.

In order for a star to become a black hole, the core of the star needs to have a mass in the order of two solar masses or more. The core will be mainly iron and fusion processes come to an end as iron fusion requires additional energy.

When the fusion reactions stop, the core collapses under gravity. The massive core will collapse to form a black hole. In the process a lot of energy is released. This causes a massive supernova explosion which blows the rest of the star into space.

As the core is only about 20% of the mass of the star, most of the star expands out to form a nebula. The core becomes a black hole which still has the same mass as the core before collapse.

So, the mass of the star is preserved as black holes have all of the mass which went into them.