Neutrino from shredded star reveals cosmic particle accelerator

Astrophysicists have traced a subatomic particle called a neutrino to its cosmic origins, a tidal disruption event located some 700 million light-years from Earth.

The new research -- published Monday in the journal Nature Astronomy -- suggests the violent destruction of a faraway star by a supermassive black hole was powerful enough to send a tiny, near-frictionless particle racing across space.

The neutrino's 700-million-mile journey was sparked by what scientists call a cosmic particle accelerator, a phenomenon born of a tidal disruption event.

When a star ventures too close to supermassive black hole, the black hole's powerful gravitational pull acts more strongly on the side of the star closest to the black hole. As a result, the star becomes pulled and stretched by gravity's tidal force.

"As the star gets closer, this stretching becomes more extreme," lead study author Robert Stein said in a news release.

"Eventually it rips the star apart, and then we call it a tidal disruption event," said Stein, a scientist at Deutsches Elektronen-Synchrotron, or DESY.

Roughly 700 million years ago, this happened to a star inside an unnamed galaxy located in the constellation Delphinus.

In April 2019, the glow of the star being pulled into the supermassive black hole's accretion disk was spotted by Zwicky Transient Facility, or ZTF, on Mount Palomar in California.

Six months later, the IceCube neutrino detector at the South Pole observed an extremely high energy neutrino speeding from same direction as the tidal disruption event, or TDE.

"It smashed into the Antarctic ice with a remarkable energy of more than 100 teraelectronvolts," said study co-author Anna Franckowiak, a former DESY scientists who is now a professor at the University of Bochum.

"For comparison, that's at least ten times the maximum particle energy that can be achieved in the world's most powerful particle accelerator, the Large Hadron Collider at the European particle physics lab CERN near Geneva," Franckowiak said.

After recording the neutrino's collision, researchers studied the TDE across the full electromagnetic spectrum. Their analysis showed there was just a 1 in 500 chance the neutrino's arrival was unrelated to the TDE.

"This is the first neutrino linked to a tidal disruption event, and it brings us valuable evidence," said Stein. "Tidal disruption events are not well understood. The detection of the neutrino points to the existence of a central, powerful engine near the accretion disc, spewing out fast particles."

And the combined analysis of data from radio, optical and ultraviolet telescopes gives us additional evidence that the TDE acts as a gigantic particle accelerator," Stein said.

Tidal disruption events fuel powerful jets that emanate from a supermassive black hole's accretion disk, spewing some of the destroyed star's matter out into intergalactic space.

When scientists designed a model to replicate the star's destruction, they found relativistic jets shoot out a succession of different types of matter, which explains why the neutrino detected by IceCube arrived half-a-year after the TDE was first spotted by ZTF's Samuel Oschin Telescope.

Many of the particles spit out by the powerful jets are electrically charged, and as a result are deflected by electromagnetic forces encountered on their journey through space.

Neutrinos, on the other hand, are tiny and extremely weak in charge, which means they pass through space without reacting with other particles and forces.

"The combined observations demonstrate the power of multi-messenger astronomy," said co-author Marek Kowalski, head of neutrino astronomy at DESY and a professor at Humboldt University in Berlin.

"Without the detection of the tidal disruption event, the neutrino would be just one of many. And without the neutrino, the observation of the tidal disruption event would be just one of many. Only through the combination could we find the accelerator and learn something new about the processes inside," Kowalski said.

As more instruments and telescopes designed specifically to target high-energy particles and their sources, including target tidal disruption events, researchers hope to make more discoveries like the one described in the new paper.

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