Re: If a black hole and a supergiant star were close to each other

A binary star system in which one star is losing material to a black
hole is the only way in which to "view" a black hole.  As the material
spirals from the donor to the black hole it creates an accretion disk.
The material at smaller radii orbit faster than that farther out and
so this creates friction and a temperature gradient.  The high gravity
allows these accretion disks to emit large doses of gamma-rays and
X-rays.  The gamma-ray and X-ray signatures are the observational
indicators of a black hole.  

Eventually the donor star will be reduced to nothing, becoming part of the
black hole.  Then of course the accretion and X-rays are gone and it
is no longer "seen".

To "see" more...
http://www.phy.mtu.edu/apod/ap970115.html