If scientists tell us that there are black holes in the universe that even light can't escape from, how can they prove they exist?

(Lansing State Journal, June 18, 1997)

Question submitted by Kristina Geer

Light is made up of particles called photons. Photons move through the galaxy at the speed of light which is 186,000 miles per second. This "energy of movement", also known as kinetic energy, is what ensures that photons are not immune to the force of gravity. Albert Einstein, in his famous Theory of Relativity, discovered that mass can be converted into energy. Therefore energy represents a certain amount of mass. So think of speeding photons as objects whose entire mass has been converted into energy. Consequently, the gravity of a black hole traps the photon and pulls it down just like any other object that passes near it.

Einstein's theories also explain that gravity is a curving of space around masses. The more matter there is in a single spot, the more the space will be curved around it because the force of gravity is greater. Therefore, a beam of light that is trying to escape a black hole cannot climb out of the "bowl" surrounding a black hole because its sides are too steep. Recently, the Hubble Space telescope sent back pictures of a galaxy known to scientists as NGC4261. The Hubble pictures revealed a swirling, glowing collection of matter that was shaped like a doughnut. Scientists believe that there may be a black hole in the center of this doughnut which contains matter equal to ten million of our suns.

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