Question

What does a black hole look like?

It looks...black! Since light cannot escape its tremendous gravity, you will never be able to see a black hole—the particles of light, called photons, must bounce back from an object to your eye in order you to see it. For example, if you tried to shine a flashlight on a black hole (no matter how big) its light would simply disappear into the black hole, and no photons would ever bounce back to be seen by your eyes. In short, you would see nothing but blackness. However, you can “see” a black hole by the characteristic bending of light near the event horizon. In fact, if you could get close enough (say, within a few kilometers) you would see what appears to be a ring of stars pulling away from a black circle. This phenomenon is caused by the bending of light towards the black hole (and thus away from your eyes, making the stars appear to pull away!) If you could get even closer to the black hole (in its photon sphere to be exact), you could actually see the back of your own head! This is because light is bent so much by the black hole’s powerful gravity that it actually travels in circles. Therefore, photons that strike your head can be seen by your eyes almost simultaneously. Likewise, if you were to peer out at the universe from within this point, you would see stars that appear to be “reflected” on opposite sides of the black hole. For a virtual trip to a black hole loyal to Einstein’s theory of General Relativity (explanations included!), check out the following weblink: http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html Check out these other NASA Q/A archives on black holes from other Ask-a-Scientist forums: Ask a High Energy Astronomer (more basic) http://imagine.gsfc.nasa.gov/docs/ask_astro/black_holes.html Ask a Space Scientist (more technical) http://image.gsfc.nasa.gov/poetry/ask/abholes.html
June 3, 2002