November 05, 2013 - SPACE - A team of researchers has discovered the first examples of black holes in globular star clusters in our own galaxy, upsetting 40 years of theories against their possible existence by using an array of radio telescopes to pick up a certain type of radio frequency released by these black holes as they eat a star next to them. Black holes in globular clusters may provide a way for them to get close enough to one another to merge into bigger black holes that may produce the ‘ripples in spacetime’ we call gravitational waves,” says Tom Maccarone, an associate professor of physics at Texas Tech. “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.”
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,” said Maccarone. “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.”
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, 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.
In 2007, Maccarone made the first discovery of a black hole in a globular star cluster in the neighboring NGC4472 galaxy. But rather than finding it by using radio waves, Maccarone found 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,” he said. “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.”
This year, he and his team discovered two examples of globular star clusters in our own galaxy which host black holes by finding radio emission by using the Very Large Array of radio telescopes in New Mexico.
“As the black hole eats a star, these jets of material are coming out,” he said. “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.”
The object shown in the Hubble image above, Messier 54, could be just another globular cluster, but this dense and faint group of stars was in fact the first globular cluster found that is outside our galaxy belongs to a satellite of the Milky Way called the Sagittarius Dwarf Elliptical Galaxy. In 1994, that astronomers found Messier 54 to be part of the miniature galaxy and not our own. Current estimates indicate that the Sagittarius dwarf, and hence the cluster, is situated almost 90 000 light-years away — more than three times as far from the centre of our galaxy than the Solar System.
Ironically, even though this globular cluster is now understood to lie outside the Milky Way, it will actually become part of it in the future. The strong gravitational pull of our galaxy is slowly engulfing the Sagittarius dwarf, which will eventually merge with the Milky Way creating one much larger galaxy.
Other researchers included Laura Chomiuk and Jay Strader at Michigan State University; James Miller-Jones at Perth Curtin University in Perth, Australia; Craig Heinke at University of Alberta in Edmonton, Alberta, Canada; Eva Noyola at the University of Texas at Austin; Anil Seth at University of Utah; and Scott Ransom at the National Radio Astronomy Observatory in Charlottesville, Virginia.
The results were published in The Astrophysical Journal and featured in the National Radio Astronomy Observatory’s ENews news bulletin. Journal Reference: Laura Chomiuk, Jay Strader, Thomas J. Maccarone, James C. A. Miller-Jones, Craig Heinke, Eva Noyola, Anil C. Seth, Scott Ransom. A Radio-Selected Black Hole X-ray Binary Candidate in the Milky Way Globular Cluster M62. The Astrophysical Journal, 2013 (in press). - Daily Galaxy.
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,” said Maccarone. “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.”
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, 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.
In 2007, Maccarone made the first discovery of a black hole in a globular star cluster in the neighboring NGC4472 galaxy. But rather than finding it by using radio waves, Maccarone found 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,” he said. “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.”
This year, he and his team discovered two examples of globular star clusters in our own galaxy which host black holes by finding radio emission by using the Very Large Array of radio telescopes in New Mexico.
“As the black hole eats a star, these jets of material are coming out,” he said. “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.”
The object shown in the Hubble image above, Messier 54, could be just another globular cluster, but this dense and faint group of stars was in fact the first globular cluster found that is outside our galaxy belongs to a satellite of the Milky Way called the Sagittarius Dwarf Elliptical Galaxy. In 1994, that astronomers found Messier 54 to be part of the miniature galaxy and not our own. Current estimates indicate that the Sagittarius dwarf, and hence the cluster, is situated almost 90 000 light-years away — more than three times as far from the centre of our galaxy than the Solar System.
Ironically, even though this globular cluster is now understood to lie outside the Milky Way, it will actually become part of it in the future. The strong gravitational pull of our galaxy is slowly engulfing the Sagittarius dwarf, which will eventually merge with the Milky Way creating one much larger galaxy.
Other researchers included Laura Chomiuk and Jay Strader at Michigan State University; James Miller-Jones at Perth Curtin University in Perth, Australia; Craig Heinke at University of Alberta in Edmonton, Alberta, Canada; Eva Noyola at the University of Texas at Austin; Anil Seth at University of Utah; and Scott Ransom at the National Radio Astronomy Observatory in Charlottesville, Virginia.
The results were published in The Astrophysical Journal and featured in the National Radio Astronomy Observatory’s ENews news bulletin. Journal Reference: Laura Chomiuk, Jay Strader, Thomas J. Maccarone, James C. A. Miller-Jones, Craig Heinke, Eva Noyola, Anil C. Seth, Scott Ransom. A Radio-Selected Black Hole X-ray Binary Candidate in the Milky Way Globular Cluster M62. The Astrophysical Journal, 2013 (in press). - Daily Galaxy.
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SIGNS IN THE HEAVENS: First Black Holes Discovered In Milky Way Star Clusters - "May Produce 'Ripples' In Spacetime"?! Updated at :
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Tuesday, November 5, 2013
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