A team of researchers reported the first-ever discovery of a black hole in a globular star cluster in our Milky Way Galaxy.
This Chandra X-ray image of the Messier 62’s central region shows the black hole M62-VLA1, orange circle. A red cross marks the cluster photometric center. Image credit: Laura Chomiuk et al.
In 2007, Dr Tom Maccarone from Texas Tech University made the first discovery of a black hole in a globular star cluster in the neighboring NGC 4472 galaxy. But rather than finding it by using radio waves, he detected it by seeing an X-ray emission from the gas falling into the black hole and heating up to a few million degrees.
“Six years ago I had made the first discoveries in other galaxies. It’s surprisingly easier to find them in other galaxies than in our own, even though they’re a thousand times as far away as these in our own galaxy are,” Dr Maccarone said.
This year, the astrophysicist and his colleagues used the Karl G. Jansky Very Large Array in New Mexico to discover a black hole in the Milky Way globular cluster Messier 62.
Messier 62 (M62), also known as NGC 6266, is a globular cluster located in the constellation Ophiuchus about 35,000 light-years away. It measures 110 light-years across and carries around 1 million times the mass of the Sun.
The newly discovered black hole, named M62-VLA1, is the so-called stellar-mass black hole, a type of black holes that comes from the collapse of a massive star.
“Globular star clusters are large groupings of stars thought to contain some of the oldest stars in the Universe. In the same distance from our Sun to the nearest neighbor, Proxima Centauri, its nearest neighbor, these globular star clusters could have a million to tens of millions of stars.”
“The stars can collide with one another in that environment. The old theory believed that the interaction of stars was thought to kick out any black holes that formed. They would interact with each other and slingshot black holes out of the cluster until they were all gone,” said Dr Maccarone, who is a co-author of the paper published in the Astrophysical Journal.
The old theory stated that the stars would kick the black holes out in the same fashion – occasionally, some black holes would have enough energy to escape the cluster, and gradually, they all would leave. While the theory may still be displaced, Dr Maccarone said it might still be somewhat true. Black holes might still get kicked out of globular star clusters, but at a much slower rate than initially believed.
“As the black hole eats a star, these jets of material are coming out. Most of the material falls into the black hole, but some is thrown outwards in a jet. To see that jet of material, we look for a radio emission. We found a few radio emissions coming from this globular star cluster that we couldn’t explain any other way.”
Dr Maccarone said seeing black holes in globular clusters may provide a way for them to get close enough to one another to merge into bigger black holes.
“These mergers may produce the ‘ripples in space-time’ we call gravitational waves. Trying to detect gravitational waves is one of the biggest problems in physics right now, because it would be the strongest test of whether Einstein’s theory of relativity is correct.”
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Bibliographic information: Laura Chomiuk et al. 2013. A Radio-selected Black Hole X-Ray Binary Candidate in the Milky Way Globular Cluster M62. ApJ 777, 69; doi: 10.1088/0004-637X/777/1/69
