The discovery of a star orbiting the center of the Milky Way galaxy provides compelling evidence that a supermassive black hole lurks there, according to a new study. Previous research had pointed to the presence of a supermassive black hole at the center of our galaxy, but the observations could still be explained by other theories. Now findings published in the journal Nature all but rule out those alternate theories, scientists say.

Using 10 years of high-resolution images collected by telescopes around the world, a team of astronomers led by Rainer Schödel of the Max Planck Institute for Extraterrestrial Physics in Germany tracked a star as it moved around the astrophysical object known as Sagittarius A (SgrA*) at our galaxy's core. The star, dubbed S2 came closest to SgrA* last spring, when it was 17 light-hours (or three times the distance from the sun to Pluto) away from SgrA*, which acts as a compact source of radio waves. S2 completes its orbit in 15.2 years and travels nearly 200 times as fast as the Earth moves around the sun, the researchers found. "We are now able to demonstrate with certainty that SgrA* is indeed the location of the central dark mass we knew existed," Schödel says. "Even more important, our new data have 'shrunk' by a factor of several thousand the volume within which those several million solar masses are contained." (The most recent model calculations estimate that the black hole's mass is roughly 2.6 million times that of the sun.)

According to the report, the new results eliminate the possibility that a compact cluster of neutron stars, a stellar-size black hole or low mass stars could be responsible for the radio waves emanating from SgrA*. In theory, SgrA* could be a hypothetical star comprised of elementary particles known as bosons. But as study co-author Reinhard Genzel of the Max Planck Institute points out, "even if such a boson star is in principle possible, it would rapidly collapse into a supermassive black hole anyhow."

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