Black Dwarfs Are

Black dwarfs are

A) very common, making up the majority of the dark matter in the universe.
B) often made from very low mass protostars that never fuse hydrogen.
C) rare, for few binary systems are close enough for this merger to happen.
D) rare, for collapsing cores of over three solar masses are uncommon.
E) not found yet; the oldest, coldest white dwarf in the Galaxy has not cooled enough yet.