image- Illustration of light drawn into black hole

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What causes black holes to form at the center of galaxies?

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How did researcher Andrea Ghez discover the black holes?

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What did Ghez witness that confirmed her suspicion of a black hole?

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The question of what lies in the center of our Milky Way Galaxy has been one of science's major unanswered questions.

NSF-funded researcher Andrea Ghez has confirmed the presence of an enormous black hole at the center of our galaxy, providing new understanding of how galaxies evolve.

Black holes are normally formed from the remnants of collapsed stars. However, near the centers of galaxies it is believed that enough matter can collect from stellar collisions and the accumulation of interstellar gas to form a black hole.

A black hole consists of a large mass compacted so densely that not even light can escape its force of gravity. In 1995, Ghez began tracking the movement of 200 stars near the center of our galaxy, finding at least 20 stars moving as if they were in orbit around an invisible object about one million times the sun's mass.

Using a technique in which computers analyze thousands of high-speed, high-resolution snapshots to correct for the turbulence in the Earth's atmosphere that ordinarily blurs images, Ghez witnessed the disappearance of a star that was then the closest object to the black hole.

Whether the star was sucked into the black hole or moved behind it may never be known. A similar fate for Earth is not a concern, since the center of the Milky Way Galaxy is approximately 24,000 light years away.

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