Integral joins campaign to study high-energy neutrino source

Scientists' new discovery of 'ghost particles' could lead to answers about the biggest mysteries in the universe

Demonstrating the presence of neutrinos is extremely complicated, however, because most of the ghostly particles travel right through the entire Earth without leaving a trace. But they're everywhere. If you are tanning at noon, 65 billion neutrinos from the sun will pass through every square centimeter of you each second without any measurable interactions with the molecules of your body.

Equipped with a almost real-time alert system triggered when neutrinos of the highest energies crash into an atomic nucleus in or near the IceCube detector, the observatory - in less than a minute after the initial detection - relayed coordinates to telescopes worldwide for follow up observations. They then traced the neutrino to its origin in a gamma ray blast within the distant supermassive black hole using Fermi. The detection and follow-up observations provide a convincing explanation for a mystery that has endured for more than a century: what is the source of the high-energy cosmic rays constantly raining down on Earth from deep space?

When The IceCube Neutrino Observatory from Antarctica detected a neutrino in September, they asked for help from another telescope to find a source.

An global team of astronomers has traced a ghostly neutrino back to its source, a spinning super-massive black hole at the heart of a "blazar" galaxy some four billion light years away.

The cosmic achievement, reported Thursday by a team of more than 1,000 researchers in the journal Science, is the first time scientists have detected a high-energy neutrino and been able to pinpoint where it came from. Because they rarely interact with matter and have almost no mass - hence their sobriquet "ghost particle" - neutrinos travel nearly undisturbed from their accelerators, giving scientists an almost direct pointer to their source. They detected a flare of high-energy gamma rays associated with TXS 0506+056.

This high energy strongly suggested that the neutrino had to be from beyond our solar system.

That jet contained neutrinos - subatomic particles so tiny and hard to detect they are nicknamed "ghost particles". At the time the neutrino was detected, it did not record any burst of gamma rays from the location of the blazar, so scientists were able to rule out prompt emissions from certain sources, such as a gamma-ray burst. Because the charged particle and the light it creates stay essentially true to the neutrino's original direction, they give scientists a path to follow back to the source. Blazar is an active galaxy with twin jets of light that shoot laser beams from the poles on the axis of the black hole's rotation.

Still, blazars weren't the prime suspects in the search for the source of cosmic rays. The neutrino we're talking about had an energy of about 300 teraelconds - more than 40 times what the protons in the largest particle accelerator in the world have reached.

A worldwide team of scientists from all the groups involved worked flat out, conducting a complicated statistical analysis to determine whether the correlation between the neutrino and the gamma-ray observations was perhaps just a coincidence.

The NSF Office of Polar Programs, which manages the U.S. Antarctic Program (USAP), and the Physics Division in its Mathematical and Physical Sciences Directorate jointly oversee the operations of NSF's IceCube, the world's largest neutrino detector. Using software developed by DESY researchers, the gamma-ray satellite Fermi, operated by the United States space agency NASA, had already registered a dramatic increase in the activity of this blazar, whose catalogue number is TXS 0506+056, around 22 September. "It is accurate to say that we are all swimming in neutrinos". "This blazar is located near the center of the sky position determined by IceCube and, at the time of the neutrino detection, was the most active Fermi had seen it in a decade".



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