Is a black hole heavier than the star from which it was created?

The mass of a black hole is always much less than the star from which it formed.

A very large star such as Eta Carinae (which is expected to form a black-hole some day) is about 100 times that of the sun, Having already lost as much as 50 solar masses, blown off the star by powerful outbursts in the past.

The future of the star is not fully understood. It is possible that it will collapse in a supernova, in which most of the rest of the star will be blasted into space, forming a supernova remnant, and the core of the star will collapse. The black hole formed may have a mass of more than 3 times the sun, but much less than the mass of the original star.

So while the black hole is not heavier, it is much denser. A 3 solar mass black hole would have a diameter of about 20km.