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Diagram of various planets and objects in space and their orbits
2003

Supermassive Black Hole Discovery

Astronomer and UCLA professor Andrea Ghez builds on decades of observations and speculation, finally proving that there's a supermassive black hole at the center of the Milky Way galaxy.
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For decades, the question of what lies at the center of our galaxy was the subject of fervent scientific debate. Andrea Ghez, a UCLA professor of Physics and Astronomy, found herself orbiting around a provocative answer: a supermassive black hole. Proving this theory true wouldn’t just put an end to the arguments, it would further our knowledge of how the universe works and be remembered as one of the greatest discoveries of the century.

 

But, there were a few hurdles for her to overcome first. Despite having a mass more than 2.6 million times that of our sun, the then theoretical black hole was 24,000 light years away, shrouded by space dust that blocked visible light, and by its nature, it was invisible to direct observation.

 

None of this discouraged Ghez, who as a child, told her parents she wanted to walk on the moon. Instead of dissuading their daughter, her parents bought her a telescope.

 

Atop the dormant Mauna Kea volcano in Hawaii, Ghez and colleagues set to work with a much larger lens, the W.M. Keck Telescope. The UCLA Keck facility and its advanced infrared sensors made it possible for Ghez to experiment like no one else on earth. Its large 10-meter aperture, and the use of adaptive optics to correct for atmosphere turbulence, helped the team see through the space dust and create a map of the stars in the galactic center.

 

Because black holes do not allow light to escape, a clear picture of the surrounding stars would serve as crucial test points, allowing Ghez to determine the mass that cannot be observed directly. It turns out that these central stars were moving at a brisk 12,000 km/sec. This new calculation of their speed and orbits dramatically increased the acceptance of her theory. Further observations by Ghez led to an even clearer picture, making the theory a 99.99% certainty.

 

Since then, Ghez has received numerous awards and honors, such as the Crafoord Prize, a MacArthur Fellowship and election into the National Academy of Sciences. She has also shared her knowledge directly with the public, through a variety of documentaries, science exhibits and lectures.