Did a black hole eating a star generate a neutrino? Unlikely, new study shows

Artist illustration of the tidal disruption event AT2019dsg, where a supermassive dark hole spaghettifies and eats a star. The black hole does not consume all of the material and some is thrown back into space. Credit: DESY Science Communication Lab
A high-energy neutrino with high energy crashed into Antarctica in October 2019. It was extremely difficult to find the neutrino. Astronomers were intrigued: What could possibly be able to generate such powerful particles?

Researchers found that the neutrino was linked to a supermassive dark hole, which had just swallowed a star. The neutrino was known as a tidal disturbance event (TDE) and occurred in April 2019, the same area of the sky from which it had come. Astronomers believe that the powerful particle was a result of a monstrously violent event.

However, new research challenges that assertion.

Harvard & Smithsonian and Northwestern University, present extensive new radio observations and data on AT2019dsg, allowing the team to calculate the energy emitted by the event. The team concluded that AT2019dsg did not produce the required energy for the neutrino. In fact, the amount it produced was very "ordinary".

Black holes can be messy.

Although it might seem counterintuitive at first, black holes don't always swallow everything.

"Black holes do not look like vacuum cleaners," said Yvette Cendes (postdoctoral fellow at Center for Astrophysics), who led the study.

Cendes explains that gravitational forces can cause stars to become too close to black holes. The spiraling of the elongated material eventually heats up and forms a flash in space that can be seen by astronomers from many millions of light-years away.

"But when there is too much material, black hole can't eat them all at once," Kate Alexander, Northwestern University postdoctoral fellow and study co-author, says. She calls black holes'messy eaters'. Some of the gas is emitted back during this process, just like babies eating.

These leftovers are flung back into the space as an outflow or jet, which, if strong enough, could theoretically produce a subatomic particle called a neutrino.

A rare source of neutrinos

Using the Very Large Array in New Mexico and Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the team was able to observe AT2019dsg, some 750 million light years away, for more than 500 days after the black hole had started consuming the star. AT2019dsg is the most studied TDE. Radio observations revealed that the event's radio brightness reached its peak around 200 days after it began.

The data showed that the total energy released from the outflow was equal to 30 million years of Sun radiation. Although this sounds impressive, the neutrino that was spotted Oct. 1, 2019, would need a source 1000 times more energetic.

Alexander explained that instead of seeing the brightly emitted material, Alexander sees a fainter radio-outflow of material. We see a soft wind instead of a firehose.

Cendes says, "If this neutrino somehow originated from AT2019dsg it begs to ask: Why haven’t we spotted supernovae associated with neutrinos at this distance or nearer? They are more common and have similar energy velocities.

According to the team, it is unlikely that the neutrino was created by this TDE. Astronomers would be far better equipped to understand TDEs and the mechanism that launches neutrinos if it did.

Cendes believes that there is still much to be learned and says, "We're probably going back to check-in on it again." "This particular blackhole is still feeding."

TDE AT2019dsg, which was first detected by the Zwicky Transient Facility (Southern California), on April 9, 2019, was discovered for the first time. Six months later, the IceCube Neutrino Observatory at the South Pole detected the neutrino known as IceCube-191001A.

Further exploration of Gamma Rays and Neutrinos from Mellow Supermassive Black Holes

More information: Y. Cendes et. al., Radio Observations Of An Ordinary Outflow From The Tidal Disruption Events AT2019dsg. The Astrophysical Journal (2021). Information for the Journal: Astrophysical Journal Y. Cendes et. al., Radio Observations Of An Ordinary Outflow From The Tidal Disruption Events AT2019dsg (2021). DOI: 10.3847/1538-4357/ac110a