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For more than a decade, astronomers have questioned the origins of mysterious and fleeting bursts of radio waves from distant galaxies.
Now, scientists have discovered the first such explosion in the Milky Way and traced it to its likely source: a small, rotating remnant of a collapsed star about 30,000 light-years from Earth.
The surprise discovery provided researchers with their strongest evidence that some if not all fast radio bursts, or FRBs, are triggered by compact, highly magnetized neutron stars called magnetars – exotic objects born in the embers of supernovae.
“This is the brightest radio burst ever detected in our galaxy,” said Daniele Michilli, an astrophysicist at McGill University in Montreal who works on the Canadian Hydrogen Intensity Mapping Experiment, or Chime telescope.
The first FRB sighting occurred in 2007, when Duncan Lorimer and his student David Narkevic processed archived observations from Parkes’ radio dish in Australia. The intense blast of radio waves lasted less than five milliseconds and what had produced it was a mystery. Scientists have since recorded dozens more, all from beyond our galaxy.
The latest discovery took place on April 28 when the Chime telescope detected a millisecond long FRB coming from a region of the sky where a magnetar called SGR1935 + 2154 is hidden. A second, less sophisticated telescope, made with metal poles and cake tins, known as Survey for Transient Astronomical Radio Emission 2, or Stare2, quickly confirmed the sighting, along with an X-ray explosion from the same source.
Chris Bochenek, a Caltech astrophysicist who helped build Stare2, said he and his colleagues had given the project a 10% chance of detecting an FRB in the Milky Way. “When I first looked at the data, I froze and was practically paralyzed with excitement,” he said. “The fact that we have detected such an explosion in the Milky Way is surprising.”
The analysis of the signal, called FRB 200428, found that the magnetar emitted as much energy into the radio waves in a millisecond as the sun does in half a minute. Details of the discovery are published in three independent studies in Nature.
While the discovery doesn’t mean that all fast radio bursts come from magnetars, it pinpoints the objects as a source that astronomers will now look at more closely.
An important question that remains is how magnetars release such intense bursts of radiation. One idea is that magnetars are distorted by “earthquakes” which open their surfaces and release huge bursts of energy. Another is that the powerful flares of the magnetars collide with particles in space, producing intense shock waves and magnetic fields that move electrons around, releasing bursts of radio waves in the process.
Duncan Lorimer, a West Virginia University astrophysicist who was not involved in the latest work, called the discovery “an incredibly important development” that showed that the magnetars were “truly credible sources of FRB.”
“In the past, we thought about magnetars, but I think I was more prone to a one-off source like a neutron star merger,” he said.
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