A black hole that's several million times as massive as the Sun sits in the center of our Milky Way galaxy. Most of the time, it does just what the name implies: it stays dark. But every few decades or centuries, it gets a little irritated, and it produces a massive outburst of energy.
The most recent one took place about a half-century ago as seen from Earth. But an even bigger one took place about three centuries ago.
No one on Earth saw these outbursts directly. They produced mainly X-rays, and there was no way to see X-rays from astronomical objects until recently.
Instead, astronomers have discovered these outbursts by watching them light up big clouds of gas and dust near the black hole.
A team of Japanese astronomers, for example, recently discovered the 300-year-old flare by watching a cloud that's about 300 light-years away from the black hole. Using space-based X-ray telescopes, they watched the cloud light up over a period of several years. They concluded that the glow was caused by a powerful flare of energy from the black hole.
The flare probably happened when a glob of gas passed too close to the black hole -- perhaps pushed there by an exploding star. As the gas spiraled toward the black hole, it was heated to millions of degrees, causing it to produce a brilliant burst of X-rays -- X-rays that lit up the center of the galaxy.
We'll have more about the Milky Way tomorrow.
Script by Damond Benningfield, Copyright 2008
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