The center of our galaxy is a wild and woolly place-- no place for humans, or, probably, for any other life. Recently, astronomers pinpointed a black hole there by observing an X-ray nova.
Supernova explosions blow stars apart; nova explosions are titanic, but they leave a star intact. Astronomers observed such a nova explosion in the X-ray spectrum-- an extremely rare event. By studying the X-ray radiation, they found it moved into the accretion disk of a black hole. Black holes cannot be observed directly because light does not escape them, but their existence can be inferred by the effect they have on the immediate area. Accretion disks, gas and dust in furious orbit around a black hole that can be excited by energetic radiation and thus observed, are dead giveaways.
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