When multiple fields of physics come together to unravel nature’s mysteries, the game becomes much more exciting for scientists. Its a great time to be a scientist as two major fields of Physics, Astronomy and Particle Physics, are coming together to decode the Universe. One such amalgamation is the Neutrino Astronomy.
A single high energy neutrino struck Earth on September 22, 2017 and it came from a distant galaxy wrapped around a supermassive black hole. And, beginning with a blockbuster paper published on July 12 in the journal Science and signed by hundreds of scientists spread across dozens of laboratories, it’s leading giddy astrophysicists to rewrite their models of the universe.
But, What are Neutrinos?
Neutrinos are very tiny elementary particles in the Standard Model of particle physics. They are produced in cosmic rays, solar core and supernovae. Neutrinos react feebly with matter. So feebly that every second, trillions of neutrinos cross through your body without you even noticing. As a result, they are very difficult to detect. Even the best neutrino detectors (such as Super Kamiokande II) haven’t detected ‘sharp’ neutrino signals yet. They travel at a speed very close to that of light.
This neutrino travelled 4 billion light years (24 billion trillion miles) in space to reach Antarctica. This means, when the neutrino started its journey, Earth had just formed. It must have gone past countless stars, planets and asteroids to reach our little planet. All this time, it was travelling, Earth went through major transformations, saw the first micro-organisms, first plants grow, the era of dinosaurs, their extinction, the rise of homo sapiens, humans building technology and getting advanced enough to detect that neutrino that was travelling towards it. The neutrino then crashed into an atom in a block of ice in Antarctica, spat another high energy particle called muon in the IceCube Neutrino Observatory, a massive particle detector buried under the Antarctic ice and disappeared forever.
Neutrinos slam into the Earth every second, but this one was special. Scientists were ready for it. Years of refinement in technology had made them capable enough to detect a sharp neutrino signal and trace back its origin. The Fermi Gamma-ray Space Telescope — and then dozens more observatories all over the world — caught the faint signal of the neutrino’s home galaxy — termed a “blazar” thanks to its blaze of electromagnetic energy firing toward Earth — flaring.
There’s a blazar deep in space, the researchers concluded, part of the brightest family of objects in the universe: galaxies with supermassive black hole engines firing beams of energy toward Earth. And this blazar is accelerating neutrinos to enormous energies, and flinging them into our planet.
When the neutrino struck the IceCube detector, Darren Grant was sitting in his office at University of Alberta. The IceCube spokesperson and astrophysicist told him about the detection. “We detect one such signal every month. So it was a kind of routine. We had detected 11 such signals so far”, Darren told Live Science. None of them had been traced back to its source. So the alert went out, observatories all over the world pointed their telescopes at the patch of sky it came from, and then nothing happened…for days.
Astronomers didn’t detect anything in that part of the sky. There was a blazar but it didn’t appear to be the likely source. So it was just a sort of neutrino number 12 for them and they moved on.
But then, a few days later, researchers at Fermi sent out an alert: That blazar was flaring. The gamma-ray telescope had spotted it emitting eight times more gamma rays than usual, the brightest it had ever been. Something — researchers don’t know precisely what — was causing the galaxy to emit a jet of super-fast high-energy gamma photons. That same process could have emitted the neutrino.
Importance of this detection:
Blazars can act as a source of the cosmic neutrinos. This idea had been popular for many years but had fallen out over.
Researchers began to worry, that there just weren’t enough blazars in the sky to account for all the different directions cosmic neutrinos come from. This result is a “first step” and “proof of concept,” Grant said, showing first that at least some neutrinos come from blazars. However, the physics behind neutrino production from blazars is still unknown. There’s a lot to discover. Its just the beginning.