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Radio Waves Detected Coming From Center of Galaxy

Brian Handwerk
National Geographic News
March 2, 2005
 
Astronomers have detected an unusual, powerful burst of intermittent radio waves emanating from the direction of the center of our galaxy.

Now the search is on to trace the source of the mystery radio bursts, or at least find more like it. Was it a dying star "burping" its last radio emissions? Or is there something out there completely new to science?

The discovery "will cause a stampede of further observations," write astronomers Shri Kulkarni and Sterl Phinney in tomorrow's issue of the science journal Nature. They're in the Division of Physics, Mathematics, and Astronomy at the California Institute of Technology in Pasadena.

Astronomer Scott Hyman of Sweet Briar College in Virginia helped make the discovery while observing the center of the Milky Way through radio telescopes set at various wavelengths. The galaxy is full of objects that emit radio waves, including black holes and stars of various kinds. But the cause of this particular burst of radio waves has astronomers scratching their heads.

"The most spectacular aspect of this is that five bursts occurred at regular intervals of about an hour and a quarter [77 minutes]," Hyman said. "They were at a constant intensity … and each burst had basically the same time profile." Each burst lasted about ten minutes.

Hyman and colleagues reported their findings in this week's Nature.

Transient radio emissions are not particularly unusual. They generally occur, at many different wavelengths, in conjunction with large releases of energy such as occur during deaths of stars. Binary systems featuring black holes or neutron stars emit radio and x-ray bursts, while supernovas emit over the entire electromagnetic spectrum.

But short-lived radio bursts are rarely detected, because radio telescopes, until recently, have only been able to focus on a relatively small area of the sky in each observation.

"We need a different way of building telescopes," Kulkarni said. "Now we have very sensitive instruments, but they have tunnel vision. They are good when you know what you want to see but not so good [for looking] at a large piece of sky and being ready to pounce on something."

Kulkarni added that discoveries like Hyman's could galvanize astronomers to press on with the development of more "wide sky" radio instruments.

Hyman's team was able to achieve a considerably wider sky view than other astronomers have.

"If we found this by just scratching the surface, imagine what's lurking out there," he said. "We may uncover many additional types of lower-energy-radio transient sources."

Source Unknown But Likely Natural

The new burst, dubbed GCRTJ1745-3009, has an unknown source. Current data cannot reveal how far away it lies in the direction of the galactic center. The center of the galaxy is about 26,000 light-years from Earth. The radio source could be a lot nearer or a lot farther—possibly even beyond the galaxy. The transmission's intriguing characteristics beg the question: Might that source be intelligent?

"There's no reason to expect anything but a natural cause," Hyman said. "There are so many classes of objects we don't know about out there."

Yet from what's known so far, the source of the radio burst seems to be of unknown type.

Hyman notes that the source could be an object like a pulsar (a pulsating neutron star) or "magnetar" (a neutron star with an extreme magnetic field), or more like a flare star (a star whose brightness fluctuates rapidly) or brown dwarf (a "failed star" that never ignited). In either case, its properties don't fit those of known sources, so it may well be an entirely new type.

"Whatever it is, it's certainly a very interesting object, that's for sure," Hyman said.

Kulkarni added that the burst might well represent a completely new type of object but suggested that it could also be a dying pulsar of a type he calls a "burper."

"It's a less fun possibility, I'll be the first one to admit," he said. "It's known that when pulsars age, they start sputtering along, so the question is, do they disappear [quickly] from the radio sky, or do they just sputter more and more, burping their way into death?"

If the latter is true, there could be hundreds of millions of such objects out there, awaiting study in what Kulkarni described as a "stellar graveyard."

The mystery may move closer to resolution later this month when Hyman and his colleagues attempt to pinpoint the location of the burst's elusive source. An observation is scheduled at the Very Large Array (VLA), a massive radio observatory on New Mexico's Plains of San Agustin, where the burst was first detected.

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