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Ghez
galaxy
lurk
the Milky Way
cosmologist

You can see the positions of the stars very accurately. If we go in to the center here, rescale it, we actually see that there are fainter stars towards the center of our field of view. And these stars are extremely important. It's the motion of these stars that reveals the presence of the black hole.
Ghez has been following the motions of these stars for the last five years. If there was no black hole, they'd be moving very slowly, but she's discovered they are circling at speeds of over 1,000 kilometers a second.
These stars that we've been watching are two light weeks from this, from the center of our galaxy. So their motion, the fact they are going a thousand kilometers per second tells us that within two light weeks there is two million times the mass of the sun of matter there.
There's only one thing in the universe this dense. Lying at the center of this necklace of spinning stars is a supermassive black hole. You can't see it, but it's there. The most destructive force in the universe is lurking at the heart of our very own galaxy, the Milky Way. The puzzle for cosmologists now is what effect it has on the galaxy around it.

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