In December 2012, scientists at the IceCube Neutrino Observatory in Antarctica detected a high-energy neutrino outburst named “Big Bird.” Now, over three years after the event, astronomers using data collected by NASA’s Fermi Gamma-ray Space Telescope believe they have located the point of origin of the neutrino, which packed energy of more than 2 quadrillion electron volts.
In a statement released Thursday, NASA said that the neutrino detected by IceCube most likely originated in 10 billion light-years away in PKS B1424-418 — an “active” galaxy that’s classified as a gamma-ray “blazer.” An active galaxy, as opposed to its inactive counterpart, is one with a compact and unusually bright core.
“The excess luminosity of the central region is produced by matter falling toward a supermassive black hole weighing millions of times the mass of our sun. As it approaches the black hole, some of the material becomes channeled into particle jets moving outward in opposite directions at nearly the speed of light,” NASA explained in the statement.
In the case of blazars, such as PKS B1424-418, one of these jets happens to point directly toward Earth, sending out a stream of high-energy neutrinos.
“Neutrinos are the fastest, lightest, most unsociable and least understood fundamental particles, and we are just now capable of detecting high-energy ones arriving from beyond our galaxy,” Roopesh Ojha, a Fermi team member at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in the statement. “Our work provides the first plausible association between a single extragalactic object and one of these cosmic neutrinos.”
Neutrinos — once described as “the most tiny quantity of reality ever imagined by a human being” — are perhaps the most exotic of all known subatomic particles. Since these “astronomical messengers” — as the IceCube lab describes neutrinos — travel across the universe without interference, they are pristine, faithfully carrying information about the cosmic event that created them. As a result, they can provide information about processes and environments that aren't available through a study of light alone, such as the origin of our universe and the nature of the omnipresent “dark matter.”
Every second, billions of neutrinos travelling at nearly the speed of light pass through Earth, but since these particles rarely, if ever, interact with matter, they are extremely hard to detect and study.
This is where the IceCube Lab at the South Pole plays a vital role. With thousands of optical sensors buried deep beneath the Antarctic ice, the lab is the perfect place to detect ghostly particles as they, on rare occasions, interact with atoms in the ice and trigger a cascade of fast-moving charged particles that emit a faint glow, called Cerenkov light.
“IceCube is about to send out real-time alerts when it records a neutrino that can be localized to an area a little more than half a degree across, or slightly larger than the apparent size of a full moon," Matthias Kadler, a professor of astrophysics at the University of Wuerzburg in Germany, and lead author of a study detailing the latest findings, said in the statement. “We're slowly opening a neutrino window onto the cosmos.”