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View Full Version : Can any particle escape from the event horizon of the black hole?


akhtar1984
Feb 25, 2010, 11:20 AM
I want to say that can any paticle, either it is virtual or real, escape from the event horizon of the black hole?

kryostar
Aug 4, 2010, 07:10 AM
Yes if it has enough velocity it can break free from the gravitational pull of a black hole

ebaines
Aug 5, 2010, 05:48 AM
yes if it has enough velocity it can break free from the gravitational pull of a black hole

Not quite right. The definition of the event horizon is the distance from the center of the black hole where the escape velocity is equal to the speed of light. Anything inside the event horizon would require a velocity in excess of the speed of light in order to escape, which of course is impossible. Thus no particle can escape based on having sufficient speed - including light photons, and hence the name "black hole."

However, Stephen Hawking showed that black holes can give off thermal radiation - and thus energy, and thus mass - and consequently over time a black hole can actually evaporate away. This effect is pronounced only for very small black holes - those that are smaller than the mass of the moon. Black holes that are larger than that (such as the "typical" black hole we think of as being the remains of a collapsed star) emit so little thermal radiation that their black body temperature is actually less than the cosmic background temperature of 2.7 kelvins. Consequently these black holes don't radiate away at all.