Astronomers still have a lot of work to do
Paul M. Sutter is a professor of physics at SUNY Stony Brook and the Flatiron Institute, as well as the host of “Ask a Spaceman” and “Space Radio” and the author of “How to Die in Space.” This post was written by Sutter for Space.com’s Expert Voices: Op-Ed & Insights.
The cosmos is a hive of activity, with stars exploding, black holes devouring everything, and high-energy radiation aplenty. Some of these occurrences manifest themselves on Earth as high-energy neutrinos, ghostly particles that seldom interact with ordinary matter. Fast radio bursts (FRBs) are brief but strong flashes of radio radiation that appear in some cases.
The source of the highest-energy neutrinos is unknown to astronomers, and the origins of FRBs are similarly unknown. The origins of both neutrinos and FRBs may be explained if they came from the same location in the sky.
But, sadly, that isn’t the case, as recent study casts doubt on the possibility of a link.
I notice a lot of dead particles
Neutrinos are among the universe’s most prevalent particles. Every second, a few trillion are passing through your body. They are not only the lightest of all known particles, but they also seldom interact with ordinary matter.
The detection of neutrinos necessitates the use of some of our most powerful devices. And I don’t mean little; I’m referring to the IceCube array in Antarctica. The IceCube facility, which is located near the geographic South Pole, is made up of dozens of strands of detectors dug into the ice sheet. When a rare neutrino collides with a water molecule, a flash of light is produced, which is seen by the detectors.
The IceCube team recorded around 11 million neutrino hits between 2008 and 2018. The great majority had moderate energies, but a small percentage had extremely high energies – some of the highest ever measured in any particle.
Those neutrinos appear to originate from all across the sky, implying that they are extragalactic. (Otherwise, they’d likely to stay within the Milky Way’s plane.) Because neutrinos don’t interact with anything else, they move in straight lines, indicating that the direction from which they originate is accurate (unlike their cousins, cosmic rays, which get deflected by magnetic fields).
Despite the millions of detections, the highest-energy neutrinos do not appear to be linked to any single galaxy or sky region. They are undoubtedly produced by some high-energy activity, although it is unclear what that process is.
The West’s quickest burst
FRBs are very enigmatic. They were discovered in 2007, and they represent some of the most intense processes in the cosmos, capable of releasing massive amounts of energy into the radio spectrum in a fraction of a second. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has generated a library of approximately 500 FRBs, with just 18 of them repeating again.
Astronomers have discovered a link between a FRB event and a magnetar, a strongly magnetic, fast rotating neutron star, suggesting a possible source. But that’s only one observation; we’ll need to do a lot more study to figure out where all FRBs come from.
Simply put, it would be fantastic if FRBs originated from the same locations in the sky as high-energy neutrinos. A linkage would be a huge insight because we don’t completely understand the fundamental causes of either. If magnetars are the true source of all FRBs and high-energy neutrinos come from the same direction, this would be strong proof that magnetars are also responsible for creating high-energy neutrinos.
A shattered puzzle
But it’s too bad they don’t. Shantanu Desai, an astronomer at the Indian Institute of Technology Hyderabad, looked at the association between millions of neutrinos and hundreds of FRBs available in public catalogs in a research recently published in the preprint database arXiv.
Desai discovered a slew of coincidental sources where a FRB was only 3 degrees away from a neutrino. (The 3 degrees is arbitrary, although it is close enough to the measurement uncertainty to be considered “nearby.”) Desai then compared the number of FRBs with no neutrino companion to the number of FRBs with no neutrino buddy.
It seemed that FRBs were equally likely to be near or far from a high-energy neutrino, implying that there is no link.
That indicates the process that produces FRBs is unlikely to be the same as that which produces high-energy neutrinos. It also implies that astronomers will have a lot more work to perform in the future.