![]() This led Law to conclude that the radio emissions from the dwarf galaxy were the 25-year-long afterglow from the explosion of a massive star, perhaps more than 40 times the mass of the sun, which would have produced a long gamma-ray burst that went undetected. The mystery object is located inside a dwarf galaxy 284 million light years from Earth that is still forming stars: a special environment that has previously been associated with fast radio bursts and, independently, gamma-ray bursts and the formation of magnetars. It was invisible in a 2017 Very Large Array Sky Survey. It was fainter in a 2010 survey and barely visible in 2015. ![]() It then faded away over a period of 23 years. They concluded that the radio emissions first reached Earth in 1992 or 1993, though their first detection was around the source’s peak brightness in 1994. ![]() He and his colleagues discovered 10 other sets of radio observations of that area of the sky, in the constellation Boötes, that allowed them to document the object’s appearance and disappearance. We basically went through every radio survey, every radio dataset we could find, every archive in the world to piece together the story of what happened to this thing.” “Its peak brightness in the ‘90s was quite high, so it was a big, big change: about a factor of 50 decrease in brightness. “We thought, ‘That was weird,’” Law said. While the beams often miss Earth, these explosions create a telltale transient radio glow that can be detected. It was on a par with the brightest radio sources in the universe: quasars and active galactic nuclei fueled by stars and gas falling into the massive black holes in the cores of galaxies.Īn artist’s depiction of a gamma ray burst, emitted in oppositely directed beams after a massive stellar explosion. The radio source (FIRST J141918.9+394036), now too faint to show up in sky surveys but still detectable by large radio telescopes, was a bright spot in a radio survey of the sky conducted in the early 1990s by the Very Large Array in New Mexico. He and his colleagues detail their observations and conclusions in an article recently accepted by the journal The surrounding matter emits intense radio waves that slowly fade away, during which time the magnetar spins down and occasionally emits fast radio bursts, another mysterious “transient” event in the universe. Law favors the theory that the explosion – whether preceded by the merger of two very large stars or neutron stars, or marking the death of a single, massive star – produces a rapidly spinning and highly magnetized neutron star, known as a magnetar. ![]() The fact that these explosions are followed by a decades-long radio afterglow provides a way for astronomers to find the rest of these explosive events, not just those heralded by a gamma-ray burst.įinding many more gamma-ray bursts will help resolve a major question in astronomy today: What are these massive stellar explosions that generate gamma-ray bursts, and what’s left behind afterward? Perhaps only one in 100 explosions can be seen from Earth by NASA’s Fermi Gamma-ray Space Telescope, for example. 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.
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