Neutrinos Can Show How Quickly Radio Bursts Are Triggered

The elusive particles are hard to catch, but they can be a smoldering weapon, the researchers said.

For more than a decade, astronomers have pondered the origins of rapid radio explosions, short bursts of radio waves originating primarily from distant galaxies. At the same time, scientists have also discovered high-energy neutrinos, ghost particles from outside the Milky Way, whose origin is also unknown.

A new theory suggests that two imaginative signals can come from a single cosmic source: highly active and magnetic neutron stars, the so-called magnetars. If so, it can add details about how quickly radio or FRB bursts occur. However, it is difficult to find a smoking weapon capable of blocking a neutrino and a radio that explodes from the same magnetar at the same time, because these neutrinos are rare and difficult to find, says Brian Metzger, an astrophysicist at Columbia University. He and his colleagues described the idea in a study published Sept. 1 on arXiv.org.

While this article offers a possible connection between what I think are two of astrophysics’ most exciting puzzles, says Justin Vandenbroucke, an astrophysicist at the University of Wisconsin-Madison, who has researched neutrinos but is not involved. in new activities.

More than 100 rapid radio bursts were detected, but most were too far away for astronomers to see what was directing the energy beams. Dozens of possible explanations have been discussed, from star collisions and supermassive black holes to rotating star bodies called pulsars and rotating black hole pulsars (SN: 10/1/18). Some astronomers have even made phone calls to aliens.
But in recent years, magnets have become a major competitor. We don’t know what the engines are for fast radio bursts, but he’s increasingly convinced some of them are from flashing magnets, Metzger said.

That confidence was boosted in April when astronomers discovered the Milky Way’s first radio to explode (SN: 6/4/20). The explosion was close enough – about 30,000 light-years away – that astronomers could trace it back to an active young magnetar called SGR 1935 + 2154. It was really like a Rosetta Stone to understand FRBs, says Vandenbroucke.

There are many ways that magnets can transmit explosions, Metzger said. For example, radio wave explosions can originate near the surface of the neutron star. Or the shock waves formed after a magnetar caused by a vigorous eruption similar to that emitted by the sun can create radio waves.

Only these shock waves can produce neutrinos and fast radio pulses at the same time, Metzger said. Here’s how it works: Some magnetars repeatedly fire torches and enrich their surroundings with charged particles. Importantly, each flare hollows out a few protons from the surface of the neutron star. Other situations can give a magnetar a mixture of electrons, but the protons only come from the magnetar itself. If the magnetar has a mixture of electrons, adding protons to the mixture sets the stage for the double dose of cosmic phenomena.

When the next torch meets the protons released by the previous torch, it will accelerate the protons and electrons at the same speed in the same direction. This gentle electronic dance can lead to a rapid burst of radio waves by converting the energy of the movement of electrons into radio waves, Metzger said. And protons can undergo a chain reaction resulting in only one high-energy neutrino per proton.

Together with astrophysicists Ke Fang from Stanford University and Ben Margalit from the University of California at Berkeley, Metzger is calculating the energies of all the neutrinos generated by the rapid radio explosion in April. The team found that these energies were consistent with those observed by the IceCube Neutrino Observatory in Antarctica.

But IceCube did not find any neutrinos from this magnetar in April, says Vandenbroucke, who has been looking for signs of neutrinos from the rapid radio explosion in IceCube data since 2016. However, this is not surprising. Since neutrinos are expected to be scarce in FRBs, identifying neutrinos will be difficult and likely require a particularly bright magnetic field to focus directly on Earth.

Vandenbroucke bet his students on other aspects of their research but said he would not spend any money to see a neutrino from a rapid radio explosion in his life. There is so much uncertainty, he says.

However, he is optimistic. Even the detection of a neutrino from a [rapid radio explosion] is a discovery, and it will only take one lucky FRB to produce a visible neutrino, he said.

 

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