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Q&A: Black Holes

Q:
I would like to know what exactly is in a black hole. Does anyone know? Is there a way to get a satellite near one to bring back images from inside the hole? What makes the black hole so devastating? The idea of them has always seemed so frightening.

A:
According to the laws of general relativity, there should be a point of infinite density inside of the black hole, which we call the singularity. At that point, the laws of physics as we know them break down, so the truth is we don't really know what is going on inside. In the very long term future we might be able to get a satellite to travel close to the edge of a black hole (the edge is called an event horizon) but it would have to be a very special satellite since the tidal forces (see the Chandra article describing tidal forces here: http://chandra.harvard.edu/chronicle/0104/tidal/index.html) are so strong that they would tear apart any known material. It doesn't seem that it would be possible to send a satellite into the black hole and then have it return to us because once an object is inside of the event horizon it cannot escape. There are very interesting ideas about traveling into the black hole, through a tunnel called a worm hole, and coming out the other end at a white hole, but these are only fantastic ideas and hints from relativity equations, nothing solid.

Sagittarius A*
Sagittarius A*
Outside of the event horizon, a black hole isn't as devastating as it sounds. The force of gravity falls off quickly, as an inverse square of the distance. In the center of our galaxy we believe there is a massive black hole, but even the stars quite close to it are not falling in or being torn apart. They are just orbiting it and have been orbiting for many many years. We live very far away from the center of the galaxy, in a spiral arm, and we are in no danger at all of getting close to the edge of the Milky Way's black hole. So there is nothing to be frightened of, but it is very nice to think of what is really inside of the black hole, and what happens to the objects that do fall in past the event horizon.

For more information on black holes, see the black hole field guide:
http://chandra.harvard.edu/xray_sources/blackholes.html.

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