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Most stars are born in binary systems. If a binary pair survives
after the more massive of the two goes Supernova, then we are left with a
compact object (neutron star or black hole) in orbit around a normal star.
Just as we saw Nova and Supernova being created from White Dwarfs in orbit
around Red Giants, Neutron Stars or Black Holes can become detected if they
have a binary companion willing to feed their enourmous gravitational
potential.
- Material falling onto the compact object heats up to X-ray temperatures,
and is seen in X-ray Bursts from the system.
- The material falling on to the compact object adds angular momentum, thereby spinning it
"up" (makes it look young again!).
- The compact object may BURN AWAY its Stellar Companion, as seen in the
Black Widow Pulsar, PSR B1957+20. (diagram Here)
As the supergiant star expands, in its ``death throws'', its outer atmosphere extends far enough away that it literally is pulled away from the star to instead revolve around the compact object (black hole or neutron star). It takes a while for the matter to fall all the way into the center, and meanwhile creates a large extensive disk of material.
How a Supergiant Companion can effect a Neutron Star or Black Hole (compact object):
