NEW YORK - A cosmic mystery has literally burst on the astronomical scene. A phenomenon near the center of the Milky Way galaxy is emitting rapid but erratic blasts of high-energy radiation unlike anything observed before by astronomers.
The object was first detected by its gamma rays and X-rays and may now possibly have been observed in radio, infrared, and optical wavelengths. Scientists at the University of Chicago and Northwestern University said on Thursday [Feb 22] that the strange behavior may be the last gasps of a dying star.
They think the bursts are actually coming from two stars locked in orbit around each other, forming a binary system. One is a small but extremely dense neutron star, the remnant core of a large star that exploded as a supernova. Rapidly rotating neutron stars are often observed by their regular radio pulses, and so are called pulsars.
The outer hydrogen atmosphere of the companion star, nearing the end of its normal life, is ballooning out and crashing into the neutron star. The collisions ignite thermonuclear explosions that release the bursts of high-energy radiation being observed. The pulses from the pulsar are regular, but the explosive bursts are erratic. When first detected, they arrived at a rate of up to 18 an hour.
"This repeated bursting behavior from a pulsar is unlike anything we've ever seen," said Dr. Don Lamb, an astrophysicist at Chicago. "We're looking at the death throes of a star. We know a lot about how that happens when a star dies alone, but we don't know what happens when it's in a binary system."
The dying-star hypothesis is being proposed in a report recently submitted for publication in Astrophysical Journal Letters. Lamb developed the concept with Dr. Coleman Miller, another Chicago astrophysicist, and Dr. Ronald Taam, a physicist at Northwestern in Evanston, Ill.
The mysterious bursting pulsar, designated GRO J1744-28, was first observed in early December by the Earth-orbiting Compton Gamma Ray Observatory. The discovery is the subject of an article by scientists at the Marshall Space Flight Center in Huntsville, Ala., to be published next Thursday [Feb 29] in the journal Nature. The scientists were under instructions from the journal not to discuss their findings until then.
The observatory detected puzzling fluxes of high-energy X-rays and gamma-rays. Cosmic gamma-ray bursts rarely come more than once from the same source, which is a mystery in itself. But these bursts were unusually intense and persistent.
Other astronomers began observing the phenomenon with instruments sensitive to various regions of the electromagnetic spectrum. The X-ray Timing Explorer, a satellite launched on Dec. 30, picked up X-ray bursts that coincided with the Gamma Ray Observatory's findings. The Very Large Array radiotelescopes in Socorro, N.M., has observed radio signals in the same region of the sky, though it is not clear that they are coming from the same source.
Original file name: .CNI - New Galactic Object 2.26
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