for National Geographic News
Astronomers are closing in on proof that a supermassive black hole is the source of mysterious radio waves at the center of our galaxy, the Milky Way.
Black holes are objects whose gravitational pull is so strong that nothing, not even light, can escape. Supermassive black holes contain the mass of millions, if not billions, of suns.
Astronomers have long suspected that supermassive black holes sit at the heart of most galaxies and may be closely related to galaxy growth. But concrete proof of the existence of these black holes has remained elusive.
"There are many pieces of evidence that need to come together to really demonstrate that a supermassive black hole is at the center of our own galaxy," said Fred K.Y. Lo, the director of the National Radio Astronomy Observatory in Charlottesville, Virginia.
Lo is a member of an international team of astronomers who used an array of radio telescopes to make new high-resolution measurements of a source of radio waves at the center of the Milky Way known as Sgr A* (pronounced "Sagittarius A star").
Radio telescopes capture images of electromagnetic waves that optical telescopes can't detect.
The new measurements strengthen the argument almost beyond doubt that Sgr A* is a black hole, Lo said.
He and his colleagues report their new observations in tomorrow's issue of the journal Nature.
In an accompanying commentary, University of Maryland astronomer Christopher Reynolds wrote, "these observations provide strong evidence that Sgr A* is indeed a black hole."
Astronomers previously theorized that Sgr A* is a black hole based on observations of the stars speeding around it.
The observations showed that the object is four million times more massive than the sun and is no bigger than Pluto's orbit.
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