Gamma-ray bursts, such as that detected last year accompanying gravitational waves from the merger of two neutron stars, are rarely seen because the source of the gamma rays – a relativistic jet of material emerging from the explosive merger – must be pointing directly at Earth. “These are known as ‘orphan’ gamma-ray bursts, and many more such orphan GRBs are expected in new radio surveys that are now underway.” “We believe we are the first to find evidence for gamma-ray bursts that could not be detected with a gamma-ray telescope,” said Law, an assistant research astronomer in the Department of Astronomy at the University of California, Berkeley. Gamma-ray bursts, whose origins are still contentious, are among the most intense flashes in the universe because much of their explosive energy is collimated into a tight beam, like that from a lighthouse. NRAO image.īased on the extreme brightness of the radio source and the type of galaxy in which the flare-up occurred, Law argues that it was the afterglow of the explosion of a massive star, which would have emitted an undetected long-duration gamma-ray burst.
Now very faint, its peak brightness in 1993 was more than 50 times what it is today. The orphan burst flared and died out over a period of 25 years. That search turned up the first of what may be many “ghost” objects in the sky: in this case, an extremely bright source of radio emissions that blazed into existence in the 1990s and then faded out over next 25 years. Astronomers typically study objects that are visible night after night or explode suddenly, like supernovas, but Casey Law is scouring vast amounts of data in search of bright objects that disappear, never to be seen again.
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