A National Tsing Hua University (NTHU) astronomer was among a group of international researchers who traced the origin of a high-energy neutrino to a star’s destruction by a black hole, a rare discovery that provides a glimpse into the origins of one of the most common and least understood things in the universe, the school said on Wednesday.
Despite being one of the most abundant particles, neutrinos elude understanding.
As their name suggests, the fundamental particles have a neutral electrical charge and nearly no mass. They travel near the speed of light without being impeded by matter or most forces, much to the frustration of scientists trying to observe the elusive “ghost particle.”
High-energy neutrinos, whose energies are 1,000 times greater than those produced by particle accelerators on Earth, are an even greater mystery.
Astrophysicists have theorized that high-energy neutrinos could be produced by extreme galactic events.
The only evidence of this effect was found in 2018, when a specific high-energy neutrino was traced to a blazar 3.7 billion light years away.
However, a team of researchers who included Albert Kong (江國興), a professor at NTHU’s Institute of Astronomy, was the first to link a high-energy neutrino observation to a similarly poorly understood tidal disruption, and only the second to identify the source of a high-energy neutrino.
In a tidal disruption, a star brushes close enough to a supermassive black hole to be pulled apart in a process called spaghettification, emitting an explosive flare of radiation as the disk of star matter that forms around the black hole is absorbed.
Experts believe that the particles shot out at near light speed collide with light or other particles, creating high-energy neutrinos, although it had not been observed until now, Kong said in an NTHU news release.
In April 2019, astronomers detected a tidal disruption nearly 700 million light years away in the Delphinus constellation, Kong said.
Half a year later, the IceCube Neutrino Observatory at the South Pole detected a high-energy neutrino that it traced to the location of the tidal disruption, he said.
Under the direction of Robert Stein, a doctoral student at the German Electron-Synchrotron, researchers from NTHU, the Netherlands, Sweden, the UK, the US and other countries combined their analysis of gamma, X-ray, ultraviolet, visible light and radio wave observations to confirm the particle’s origin.
The combined evidence suggests that the tidal disruption “acts as a gigantic particle accelerator,” Stein said.
Kong, who analyzed X-ray data, said that the X-rays generated from the tidal disruption weakened at an unprecedented rate.
This either means that the disk is cooling rapidly, or the X-rays are being absorbed by the gases gradually building around the structure, he said.
“Although neutrinos are as hard to detect as ghosts, every particle brings with it important information about its star from the depths of the universe,” Kong said.
By combining observations, researchers can better understand the physical properties behind the origin of these high-energy particles, he added.
The researchers published their findings last month in the journal Nature Astronomy.
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