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Star in galactic heart confirms central black hole

By Richard Stenger

In this color-enhanced image of the galactic center, arrows show the location of a central black hole and companion star.
In this color-enhanced image of the galactic center, arrows show the location of a central black hole and companion star.

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(CNN) -- Tracing the orbit of a star around the center of the Milky Way for the first time, astronomers announced Wednesday that the observations confirmed the existence of a collossal black hole in the heart of the galaxy.

The star passes within 17 light-hours of a compact radio source known as Sagittarius A, pegged as the galactic center, and completes an oval orbit around the super hot spot every 15.2 years.

The orbital perimeter mean that the entire mass of the interior object, between 2.6 million and 3.7 million times more massive than the sun, lurks inside an area three times the size of our solar system.

The staggering density could only result from a supermassive black hole, according to physicist Rainer Schoedel, who with colleagues published the findings in this week's journal Nature.

"We can now confidently say that a black hole does indeed exist at the center of our galaxy," said Schoedel, who works at the Max Planck Institute for Astrophysics in Garching, Germany.

Scientists suspected that the galactic center harbored a black hole but had not ruled out alternative explanations for the Sagittarius A radio source, such as a dense cluster of stars or stellar material within a few light-years.

The smoking gun came from pinpointing the source of the intense energy emissions to a span of 17 light-hours, the distance that light travels in 17 hours.

"No event like this one has ever been reported," said the European Southern Observatory, which manages some international telescopes used in the study.

The astronomers found "unambiguously" that the central star is moving around Sagittarius A "like the Earth orbits the sun," the ESO consortium said in a statement.

Schoedel and colleagues, who pored over 10 years' worth of high-resolution images of the star, said further observations will provide a more accurate estimate of the central black hole's mass.

The work has "important implications for understanding how our black hole compares with those at the center of other galaxies," said Karl Gebhardt of the University of Texas at Austin, who wrote a companion piece in the October 17 Nature report.

Black holes, commonly formed from the collapse of large stars, can be described as points where so much mass is concentrated that the gravitational pull prevents anything from escaping, including light.

Scientists think many galaxies have supermassive central black holes. One theory is that they form when a massive black hole in a crowded galactic center pulls in neighboring stars and other black holes.

CNN Science Correspondent Ann Kellan contributed to this report.

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