Second Source of Gamma Rays in Milky Way Found

UC San Diego scientists have discovered a second huge source of gamma rays in the Milky Way, a black hole or a neutron star that is generating enough radiation to power 50,000 suns.

Reporting to the American Astronomical Society meeting in Seattle, research physicist Michael S. Briggs said the object is about 1,800 light-years away from Earth. This is much closer than the so-called “Great Annihilator,” the gamma ray source that is believed to be a black hole near the center of the galaxy. It is 25,000 light-years away.

Discovery of a second suspected black hole in the Milky Way is likely to spur a search for others.

“We now have two examples of this class of object (in the galaxy) and we expect to find many more,” said Jim Matteson, a leading gamma ray authority at UC San Diego. “This is very important. It is a fundamental discovery in astrophysics.”

A black hole is a collapsed star whose gravitational pull is so strong that it sucks entire stars and even light itself into its core. It produces gamma radiation when certain atomic particles collide and are annihilated.

Briggs made his discovery by using recent computer software to reanalyze data gathered from 1977-78 by a spacecraft, the High-Energy Astronomy Observatory. There was so much background radiation in the original readings that it previously was impossible to detect a single gamma source, he said.

Matteson leans toward the theory that the object Briggs discovered is a black hole. But, since other objects can produce intense gamma rays, further studies also will look for evidence of other possibilities.

One suggestion is that the gamma rays are coming from a dying star known as a white dwarf, as it gobbles up a companion star.

But Matteson contends that a white dwarf generally isn’t strong enough to capture the amount of stellar material needed to generate that much radiation. Briggs’ calculations estimate the source’s temperature at 350 million degrees Celsius--compared to the sun’s surface temperature of 6,000 degrees.

Another possibility is that the gamma ray source is a neutron star, so dense that it is only about 30 miles in diameter.

“At the moment, there is really no way to decide what the explanation is,” Matteson said.

UC San Diego researchers and others will gather more data on the suspected black hole when they go to Australia this fall to survey the galactic center using balloon-mounted imaging cameras and spectrographs.

The Soviet satellite GRANAT and a gamma detector aboard NASA’s Gamma Ray Observatory also are to be used to observe the new source, as well as look for others.