According to new estimates, a black hole devouring a star may not have produced enough energy to propel a neutrino

A high-energy neutrino blasted into Antarctica in October 2019. The neutrino caught astronomers’ curiosity since it was so difficult to detect: what could produce such a strong particle?

The neutrino was tracked back to a supermassive black hole that had just split apart and eaten a star, according to researchers. AT2019dsg, also known as a tidal disruption event (TDE), happened mere months earlier, in April 2019, in the same region of the sky as the neutrino. Astronomers believe the monstrously violent event was the genesis of the strong particle.

New research, however, calls that assertion into question.

Researchers from Northwestern University and the Center for Astrophysics | Harvard & Smithsonian provide substantial new radio observations and data on AT2019dsg in a report published this month in the Astrophysical Journal, allowing the team to compute the energy emitted by the event. The data reveal that AT2019dsg produced far less energy than was required for the neutrino; in fact, the team concludes that what it blasted out was very “ordinary.”

Black holes consume a lot of stuff

Black holes, contrary to popular belief, do not necessarily devour everything in their path.

“Black holes aren’t like vacuum cleaners,” said Yvette Cendes, the study’s lead author and a postdoctoral fellow at the Center for Astrophysics.

Gravitational forces stretch, or “spaghettify,” a star that gets too close to a black hole, according to Cendes. The elongated material eventually spirals around the black hole and heats up, causing a flare in the sky visible to observers from millions of light years distant.

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“However, when there’s a lot of stuff, black holes can’t devour it all at once,” said Kate Alexander, a research co-author and NASA Einstein fellow at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). “Some of the gas is spit out during this procedure, much like when newborns eat and some of the food ends up on the floor or on the walls.”

These remnants are thrown back into space in the form of an outflow, or jet, which might potentially produce a subatomic particle known as a neutrino if powerful enough.


“Instead of seeing the brilliant jet of material required for this,” Alexander stated, “we detect a fainter radio outflow of material.” “Instead of a strong firehose, we have a gentle breeze.”

Neutrinos from an unexpected source

The researchers observed AT2019dsg, 750 million light years distant, for more than 500 days after the black hole began devouring the star, using the Very Large Array in New Mexico and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. AT2019dsg is the most well-studied TDE to date, with comprehensive radio studies revealing that the radio brightness peaked about 200 days after the event began.

The entire quantity of energy in the outflow, according to the statistics, was comparable to the energy emitted by the Sun during 30 million years. While it may sound amazing, the strong neutrino discovered on Oct. 1, 2019, would need a 1,000-fold greater energy source.

“Instead of seeing the brilliant jet of material required for this,” Alexander stated, “we detect a fainter radio outflow of material.” “Instead of a strong firehose, we have a gentle breeze.”

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“If this neutrino came from AT2019dsg in any way, it begs the question: Why haven’t we seen neutrinos linked with supernovae at this distance or closer?” Cendes remarked. They’re a lot more prevalent, and their energy velocities are the same.”

The team comes to the conclusion that the neutrino did not originate from this particular TDE. Even if it did, astronomers are still learning about TDEs and how they launch neutrinos.

“We’ll probably check in on this one again,” Cendes said, adding that there’s still a lot to learn. “This specific black hole continues to eat.”

TDE AT2019dsg was found by the Zwicky Transient Facility in Southern California on April 9, 2019. The IceCube Neutrino Observatory at the South Pole identified the neutrino, known as IceCube-191001A, six months later.

The National Science Foundation and NASA funded the study, “Radio observations of an ordinary outflow from the tidal disruption event AT2019dsg” (award numbers HST-HF2-51403.001-A and NAS5-26555). Tarraneh Eftekhari, a postdoctoral fellow at CIERA, is one of the Northwestern co-authors.

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