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A Science Perspective on Black Holes

What happens when things are swallowed by black holes? Physicists think they know the answer, but they've never watched it happen live before. Thanks to new observations by astronomers at the Max Planck Institute, they will have the chance in about three years, when a cloud of space dust is swallowed up by the gigantic black hole that resides at the center of our Milky Way Galaxy.

dust cloud black hole.bmp
Gas cloud being sucked in: overlaid images from 2002 (red), 2007 (green), 2011 (blue).

The science that we know says that when an object is sucked into a black hole, x-rays should burst out. Like watching a collosal bug zapper, you would see the doomed matter fly into the event horizon with a bright spark, never to be seen again. The event horizon is an invisible line in space around a black hole: when you cross it you can never escape.

This sounds scary, but if you stay outside of this line, you don't have to worry. Everything would be the same as if a star of the same size were there.  If our sun suddenly became a black hole, Earth would continue orbiting as if nothing had happened; we would not be sucked in (we would be very cold and dark however!)

Another scary thought is the prospect of black holes gobbling more and more matter in until eventually they consume the entire universe! Fortunately, there is a mechanism that prevents this as well. Things eaten by black holes are not truly lost forever. Due to Stephen Hawking and Jacob Bekenstein applying quantum mechanics to black holes, we believe that they actually spit particles back out.

Hawking.jpg
Stephen Hawking

There is disagreement among scientists over how exactly particles escape the apparently inescapable black hole. Perhaps the particles can free themselves via quantum tunneling (another fascinating phenomenon caused by quantum uncertainty.) When black holes are small enough, this spitting out will evaporate them away completely to nothing. A black hole that weighs as much as a large house would evaporate in less than one second!  A black hole the size of our sun however will last nearly forever if left alone.

Image credits: (1) ESO/MPE; (2) Zero Gravity Corp.

Tom Hartsfield
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