Astronomers have found an incredible cosmic connection. An elusive high-energy neutrino detected in Antarctica has been traced back to its likely origin: a star being ripped apart by a supermassive black hole 700 million light-years from Earth.
As reported in Nature Astronomy, the IceCube Neutrino Observatory located at the South Pole spotted the neutrino with an energy 30 times higher than that we can produce when colliding protons in particle accelerators like the Large Hadron Collider. The researchers were able to track this neutrino back to its source in a particular region of the sky and realized something else had also been detected there. About six months prior, in the same part of the sky, astronomers had detected a tidal-disruption event (TDE).
A TDE happens when a star gets too close to the supermassive black hole at the center of its galaxy. When that happens, the tidal forces can pull material from the star feeding it to the black hole. The heated material is an incredibly bright source of light. The timing of the events suggests TDEs could be responsible for the production of Ultrahigh Energy Cosmic Rays (UHECRs), the highest energy particles in the universe.
Neutrinos are subatomic particles that on Earth can only be produced by powerful accelerators. They are incredibly light and hardly interact with matter. As you read this, about 100 trillion neutrinos from the Sun are going through your body. Neutrinos are not the only cosmic rays out there but to push them to the energy detected here, you really need something powerful.
"The origin of cosmic high-energy neutrinos is unknown, primarily because they are notoriously hard to pin down," Dr Sjoert van Velzen, onwe of the paper's lead authors who was at NYU at the time of the discovery, said in a statement. "This result would be only the second time high-energy neutrinos have been traced back to their source."
The link between the two events has a single chance in 500 to be coincidental, but the team had to explain the time delay between the two. In a second paper, also in Nature Astronomy, the team detailed a theoretical model to explain what’s going on. The TDE material is hot enough to produce X-rays but as it expands, cools enough to block those X-rays. This blocking actually creates a cosmic particle accelerator producing, among other particles, high-energy neutrinos like the one detected in Antarctica.
"This is the first neutrino linked to a tidal disruption event, and it brings us valuable evidence," explained co-lead author Dr Robert Stein from the Deutsches Elektronen-Synchrotron (DESY) explained in a statement. "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."
TDEs are fascinating. Just recently, researchers reported a flaring black hole that is regularly ripping its star apart.