Binary Star Systems
Often stars are formed in binary systems
Since they have unequal masses, the more massive star will evolve faster - and reach the end of its main sequence lifetime
In some cases, the supernova of the primary star will not disrupt the binary system and a COMPACT BINARY is formed
Mass transfer can then occur from the main sequence star onto the collapsed, compact companion star - which can be a WHITE DWARF, NEUTRON STAR or BLACK HOLE
Notes:
The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades.