Q&A: Black Holes

Q:
In one of your pictures you explain that the bright lights are black holes. I have always been told that black holes cannot be seen. Could you please explain this to me?

A:
No light of any kind, including X-rays, can escape from inside the event horizon of a black hole. The X-rays Chandra observes from the vicinity of black holes are from matter that is very close to the event horizon of black holes. Matter is heated to millions of degrees as it is pulled toward the black hole, so it glows in X-rays.
http://chandra.harvard.edu/xray_sources/blackholes_stellar.html
http://chandra.harvard.edu/resources/faq/black_hole/bhole-33.html
http://chandra.harvard.edu/resources/faq/black_hole/bhole-22.html
http://chandra.harvard.edu/resources/faq/black_hole/bhole-17.html.