Study reveals the source of one of the most elusive particle of the universe

These high-energy particles are nearly impossible to track down. But for the second time ever, we've done just that.


Scientists have, for the first time, gathered observational evidence for elusive, high-energy particles that come from some of the most violent events in the universe.

In a study published Monday in the journal Nature Astronomy, astronomers gathered the first evidence tracing tiny, subatomic particles called neutrinos to a black hole tearing a star apart.

In this illustration of a black hole, jets of material fall in while more are ejected in a jet. DESY, Science Communication Lab

HERE'S THE BACKGROUND If you're a wandering star in the cosmos, the last place you want to be is near a black hole.

When an unassuming star gets too close to a black hole, the gravitational force of these massive cosmic beasts tears the star apart into shreds of gas in a gruesome process known as spaghettification (shredding the star into long, thin spaghetti strands).

These types of events have been thought to produce high-energy neutrinos. Neutrinos are a neutral, subatomic particle with a tiny mass that's close to zero — smaller than the mass of any other known particle, excepting photons. Although these particles outnumber any other particles in the universe, they rarely ever interact with other matter which makes them nearly impossible to detect.

In 2006 and 2014, a NASA-funded experiment, the Antarctic Impulsive Transient Antenna, detected extremely high-energetic neutrinos in Antarctica that seemed to have traveled through the Earth. The rare findings sparked rather imaginative, but erroneous, rumors that scientists discovered a parallel universe from which these particles emerged.

"The origin of cosmic high-energy neutrinos is unknown, primarily because they are notoriously hard to pin down," Sjoert van Velzen, a postdoctoral fellow in New York University's Department of Physics, and one of the lead authors of the new study, said in a statement. "This result would be only the second time high-energy neutrinos have been traced back to their source."

Neutrinos are produced by powerful accelerators on Earth, but have only been detected once before in 2018 with their source being an active galactic nucleus called a blazar, which produces a powerful jet stream that faces our view from Earth.

WHAT'S NEW — Using a combination of ground-based and space telescopes, a team of astronomers were able to not only detect neutrinos but trace them back to Tidal Disruption Events (TDE).

TDEs are what happens when a star gets too close to a black hole. In these events, a portion of the star's mass is captured into an accretion disc of debris that swirls around the black hole after it is shredded to streams of gas.

This particular event was discovered on April 9, 2019, by the Zwicky Transient Facility (ZTF), a robotic camera at Caltech's Palomar Observatory in Southern California and dubbed AT2019dsg.

The star-shredding event occurred over 690 million light-years away in a galaxy called 2MASX J20570298+1412165, located in the constellation Delphinus.

These types of extreme events can accelerate particles to nearly the speed of light, and those speedy particles can then collide with other particles or with light itself to produce neutrinos.

"Astrophysicists have long theorized that tidal disruptions could produce high-energy neutrinos, but this is the first time we've actually been able to connect them with observational evidence," Robert Stein, a doctoral student at the German Electron-Synchrotron (DESY) research center in Zeuthen, Germany, and lead author of the new study, said in a statement.

The study suggests that the accelerated particles produced by TDEs could generate neutrinos in three particular regions, the outer disk by colliding with ultraviolet light, in the inner disk by colliding with X-ray light, and in the outflow of particles being ejected from the black hole by colliding with other particles.

For the AT2019dsg event, the researchers behind the study believe that the neutrinos originated from the particles colliding with ultraviolet light since the energy of the particles was more than 10 times greater than the energy that can be achieved by particle colliders on Earth.

"Tidal disruption events are incredibly rare phenomena, only occurring once every 10,000 to 100,000 years in a large galaxy like our own," S. Bradley Cenko, Swift Principal Investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. "Multiwavelength measurements of each event help us learn more about them as a class, so AT2019dsg was of great interest even without an initial neutrino detection."

Editor’s Note 2/23: A previous version stated that neutrinos have less mass than photons. This has been corrected. A caption on an image used has also been clarified to state that it is an illustration.

Abstract: Cosmic neutrinos provide a unique window into the otherwise hidden mechanism of particle acceleration in astrophysical objects. The IceCube Collaboration recently reported the likely association of one high-energy neutrino with a flare from the relativistic jet of an active galaxy pointed towards the Earth. However a combined analysis of many similar active galaxies revealed no excess from the broader population, leaving the vast majority of the cosmic neutrino flux unexplained. Here we present the likely association of a radio-emitting tidal disruption event, AT2019dsg, with a second high-energy neutrino. AT2019dsg was identified as part of our systematic search for optical counterparts to high-energy neutrinos with the Zwicky Transient Facility. The probability of finding any coincident radio-emitting tidal disruption event by chance is 0.5%, while the probability of finding one as bright in bolometric energy flux as AT2019dsg is 0.2%. Our electromagnetic observations can be explained through a multizone model, with radio analysis revealing a central engine, embedded in a UV photosphere, that powers an extended synchrotron-emitting outflow. This provides an ideal site for petaelectronvolt neutrino production. Assuming that the association is genuine, our observations suggest that tidal disruption events with mildly relativistic outflows contribute to the cosmic neutrino flux.