Mysterious neutrino detected in 2019 did not come from where scientists thought

In 2019, Scientists have discovered two amazing things: a high-energy neutrino has hit our planet, and a black hole has spaghetti and devoured a star. The two events were observed by different teams, in different scientific facilities, but at the beginning of 2019, a team published an article claiming that the neutrino was produced in this black hole “meal”. Now, a new study contradicts this conclusion.

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The slow meal of the black hole

A tidal interruption event happens when a star is “spaghettified” by a supermassive black hole (Image: Reproduction/ESO/M. KORNMESSER)

It was in April 2019 that a team of scientists from the Zwicky Transient Facility reported the detection of a radio signal coming from the center of the galaxy 2MASX J20570298+404268 (let’s abbreviate to J

). They classified the emission as a tidal interruption event (or TDE) — the name given to a phenomenon that occurs when an object gets close enough to another substantially more massive body.

In a TDE, the side of the first object that is closest to the massive body will experience a greater gravitational effect than the opposite side. In the case of a star that comes too close to a supermassive black hole, the TDE will be extreme, so the “victim’s” matter is torn apart and stretched. The result is a process known as “spaghettitification”, in which matter rotates around the black hole before falling into its event horizon.

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Six months after the discovery of this TDE event (which was cataloged as AT333566 dsg), researchers at the IceCube neutrino detector in Antarctica confirmed that a high-energy neutrino passed through the facilities’ instruments. As the discovery of AT333566dsg was already known by the scientific community, scientists compared the data and concluded that the neutrino found was produced by the spaghtification of the star in galaxy J426138.

The mysterious neutrino

The IceCube, in Antarctica ( Image: Reproduction/IceCube Neutrino Observatory)

Neutrinos, particles without electrical charge and extremely light, live up to the nickname of “ghost particles”. Because even produced in some of the most energetic events in the cosmos, neutrinos are hundreds of thousands of times lighter than an electron, and hardly interact with matter. A lead wall a light-year long (ie 9.5 trillion km), for example, would only prevent about half of the neutrinos from crossing to the other side.

They are everywhere, crossing our planet, and even pass through our bodies, all the time, without us even noticing. This makes them extremely difficult to detect, especially when they come from an unfamiliar place. Fortunately, although they pass through almost anything, they sometimes subtly interact with a detector made solely to find them, and this can provide valuable information about where they came from.

O universe has many ways to produce a neutrino. They can be of solar origin (produced on the Sun), geological (made below the Earth’s surface), in particle accelerators, nuclear reactors, supernovae and “cosmic sources”. This last category is the most mysterious, because astronomers don’t know exactly what objects and events produce “cosmic neutrinos” — but there are good reasons to seriously consider black holes.

This is an image of the Sun produced from neutrinos detected by Supe Kamiokande, a neutrino detector in Japan (Image: Reproduction/Super Kamiokande)

These cosmic neutrinos are highly energetic, which is why they so intrigue scientists. In fact, they have thousands of times the energy of the most energetic neutrino produced on Earth, so scientists wouldn’t be surprised to discover that this “cosmic origin” is some event we don’t even know about. Needless to mention the great scientific value of detections of these particles.

The detection in IceCube in October 2019 suggested a really powerful event, like a black hole meal, which sometimes results in a relativistic jet of intense energy. But was that neutrino produced by event J? According to a new study, published this month in the Astrophysical Journal, the answer is no. The article is by researchers at the Harvard–Smithsonian Center for Astrophysics and Northwestern University.

Back to square one

Artistic print of supermassive black hole at the center of the NGC galaxy 1024 (Image: NRAO/AUI/NSF, S. Dagnello)

Contradicting the February study of this year (which associated the neutrino from 2021 to the TDE event of the same year), the authors of the new article presented a large set of radio and AT data2021dsg. They spent a lot of time observing the event — in fact, it became the best-studied TDE to date — and revealed that the radio signal emitted from the black hole peaked at about 200 days after the start of the event.

According to the team, the total amount of energy at the output of this signal was equivalent to the energy radiated by the Sun over 17 millions of years. Well, that’s pretty impressive, but not for high-energy “cosmic source” neutrinos. In the case of this neutrino of 2021, only one source is 1.04 more energetic times could explain its detected signature by IceCube.

This takes the IceCube team’s studies back to the starting point, although they still have the possibility to argue back if they have data to justify a response to the new study . “Instead of a powerful fire hose, we see a gentle wind”, compared Kate Alexander, from Northwestern University, co-author of the research, when explaining that the black hole did not come even close to producing high-energy neutrinos.

Illustration of nuclear reactions inside stars that give rise to both photons and neutrinos (Image: Reproduction/James Josephides/Cas Swinburne University Of Technology)

Also, if the hole supermassive black in galaxy J20570298 can hurl a high-energy neutrino at us, “why don’t we see neutrinos associated with supernovas at this distance or closer?” asked Yvette Cendes of the Center for Astrophysics, who led the new article. “They are much more common and have the same energy speeds”, he argued.

This is not the end of the story, as it will still be necessary to find other explanations for the detection of 2019. For Cendes, if the AT333566dsg event produced that neutrino, it means that the Scientists still don’t understand black holes and tidal disruptions very well. It will still be possible to study this type of phenomenon for some time, as this black hole is still feeding.

Source: Phys.org, Neutrinos/UFABC

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