Radio telescopes have picked up intense bursts of low-frequency static from a mysterious source that may lie hidden near the center of our Milky Way galaxy. The flares erupted five times in 2002, but the source has since vanished. Puzzled astronomers think they caught a new kind of sporadic explosion, but they must find the object again to verify the cause.
Most cosmic outbursts generate radio waves, which radio telescopes can detect through the dustiest parts of space. But the giant telescopes stare at such small parts of the sky that they miss most sudden belches of radio signals. To address this shortfall, early in 2002 researchers started using the Very Large Array of 27 radio telescopes in Socorro, New Mexico, to occasionally monitor the galaxy's center--the most active part of the sky.
The effort paid off. In September 2002, the telescopes spotted five bursts from a new object called GCRT J1745-3009, named for its sky coordinates. Each flare lasted about 10 minutes, separated by more than an hour of calm. The flares were as bright as any other radio source in the galaxy's dynamic core, including the turbulent remnants of supernova explosions, says radio astronomer Scott Hyman of Sweet Briar College in Virginia. Hyman and his students began analyzing the events in 2004 after the images--originally taken by a different group--became publicly available.
The flares appeared so powerful that Hyman's team, which reports its discovery in the 3 March issue of Nature, believes they arose from a newly discovered class of violent events. The source could have a physical connection to an expanding cloud of gas and dust from an old supernova that appears next to the site of the flares, Hyman notes. However, there is a chance that the object is actually much closer to us than the center of the galaxy. A fainter nearby explosion could appear as bright in the sky as a distant, powerful burst. For that reason, Hyman's team has not ruled out a lower-energy source, such as magnetic outbursts from a dim "failed star" called a brown dwarf.
The exciting object will spark a "stampede" of new observations as astronomers try to determine its distance, predicts astrophysicist Shrinivas Kulkarni of the California Institute of Technology in Pasadena. His favorite explanation is that the radio telescopes witnessed the last gasps of energy from a weakly spinning neutron star, called a pulsar. "Old pulsars may wheeze and burp away as they approach their deaths," he says.