What's Causing These Mysterious Radio Bursts From Beyond Our Galaxy?

The last instant of a neutron star being eaten by a black hole. Dana Berry/NASA

Neutron stars are so dense that sometimes not even black holes can tear them apart. When one falls whole into a black hole, the black hole swallows it whole. Without material being disrupted, we have a hard time to tell such an event has taken place. At least until now. A new study has claimed that extremely powerful fast radio bursts (FRBs) are generated in the last instant before a neutron star collides with a black hole.

FRBs are incredibly powerful emissions of radio waves lasting only for a few milliseconds. The first was discovered in 2007, in archived data from the Parkes radio telescope in Australia. So, far only 11 have been discovered and only one of them was discovered “live”. The discovery of that event was quickly followed up by observations of the same area in many different wavelengths, but they couldn’t see any object responsible for the FRB.

The new research, which will be published in the Astrophysical Journal Letters, describes how the FRB could be powered by a gigantic cosmic battery. When a black Hole passes within the neutron star’s magnetic field, they form an electronic circuit, and as the objects rotate, plasma flows along the magnetic field lines generating an electric current between them. Some of this energy is turned into radio waves and as they get closer, the luminosity of the radio waves increaseas until they merge. The FRB is the peak luminosity before the merger, and the study predicts the presence of a second peak after the merger when the neutron star’s magnetic field migrates to the black hole and then snaps violently causing the second fast radio burst.

According to the study, high sensitivity radio telescopes should be able to observe an increase in the intensity of radio waves before the final FRB, as well as detecting a second burst when the magnetic field of the neutron star moves onto the black hole.

Black holes and neutrons stars are two possible ways a star could end after it goes supernova. Only the biggest stars turn into black holes. Scientists are interested in black hole-neutron star pairs as they should be emitting a lot of gravitational waves.

"In the event of a neutron star-black hole gravitational wave detection, a coincident electromagnetic detection, such as an FRB, may be possible with a telescope such as CHIME, which is optimally located with respect to the LIGO detectors." Dr Chiara Mingarelli, lead author of the study, told IFLScience. "CHIME, in fact, predicts that they may detect up to 10,000 FRBs per year."

This study doesn’t claim that neutron star-black hole binaries explain every single FRB event, but they are probably the cause of a fraction of them. Curiously, some events that looked like FRBs, called perytons, are actually produced by people opening the door of their microwave oven before the timer has got to zero. 

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