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A Wild Ride

July 6, 2021

One of the biggest roller coaster rides in the Milky Way Galaxy is a star known as S2. It orbits the black hole at the galaxy’s heart. At its closest, it’s just 11 billion miles from the black hole. And pulled by the black hole’s powerful gravity, it reaches a top speed of almost three percent the speed of light.

Perhaps more important for astronomers, the star confirms the existence of the black hole. In this 2010 interview, Andrea Ghez, an astronomer at UCLA, explains.
GHEZ: The most definitive proof you can get of a supermassive black hole is to show that things are moving around under the gravitational influence, and from that motion you can show what the mass is directly. There’s no question there. It’s very much like the planets orbiting the Sun. From those planets’ orbits you can get the mass of the Sun and the orbit also tells you a size.

Ghez and her colleagues, along with a team led by Reinhard Genzel, have been watching S2 and other stars near the black hole for decades. Their work showed that the black hole is four million times the mass of the Sun. For their work, Ghez and Genzel shared last year’s Nobel Prize for Physics.

S2 is big, young, and hot. At the peak of its orbit, it’s about 170 billion miles from the black hole. After that peak, the star plunges back toward the black hole — continuing its roller-coaster ride through the heart of the galaxy.

More tomorrow.

Script by Damond Benningfield

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