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UD researcher Tom Gaisser (left) and senior electronics
instrument technician James Roth stand before the marker for the
geographic South Pole. UD was part of the international
collaboration that built the IceCube Neutrino Observatory in the
Antarctic ice and its IceTop surface array of detectors.
science team that includes researchers from the University of Delaware
has found the first evidence of a source of what astronomers call "ghost
particleshigh-energy neutrinos that can travel unhindered over
billions of light years from the most extreme environments in the cosmos
The observations, made by the IceCube Neutrino Observatory at the
AmundsenScott South Pole Station and confirmed by telescopes around the
world and in space, help answer a more than century-old riddle about
what cataclysmic forces can send neutrinos and cosmic raysparticles
smaller than an atomspeeding through the universe nearly as fast as
Two papers publishing July 13 in the journal Science point to a giant galaxy containing a blazar as a source of high-energy neutrinos detected by the National Science Foundation-supported observatory.
This blazar, designated by astronomers as TXS 0506+056, was first
singled out following a neutrino alert sent by IceCube on Sept. 22,
2017. The first paper explains the new discovery and the second paper shares information from observations made over the past 10 years that supports these conclusions.
This is the smoking gun, said Thomas K. Gaisser, Martin A.
Pomerantz Chaired Professor of Physics and Astronomy at UD. Active
galaxies have always been the leading contender for producing
high-energy cosmic rays and neutrinos, but we didnt have the evidence
Equipped with a nearly real-time alert systemtriggered when a very
high-energy neutrino collides with the nucleus of an atom in the
Antarctic ice in or near the IceCube detectorthe observatory broadcast
coordinates of the Sept. 22 neutrino alert to telescopes worldwide for
Other observatories, including NASAs orbiting Fermi Gamma-ray Space
Telescope and the Major Atmospheric Gamma Imaging Cherenkov Telescope,
or MAGIC, in the Canary Islands, detected a flare of high-energy gamma
rays associated with TXS 0506+056, further implicating the blazar as the
most likely source.
For the scientists, it was a bit of a surprise.
It wasnt in the list of potential sources we were looking at, Gaisser said. This one never popped up before.
The IceCube team refers to blazar TXS 0506+056 as Texas. Youll
find it in the night sky just off the left shoulder of the constellation
Orion about 4 billion light years from Earth.
Move this whole section up, swapping places with the section above it.
this artist's rendering, the IceCube Lab at the South Pole is seen with
an aurora. In this rendering, based on a real image of the IceCube Lab,
a distant source emits neutrinos that are detected below the ice by
IceCube sensors, called digital optical modules or DOMs.
A blazar is a supermassive black holewith material whirling around
it, and huge jets of material bursting from itat the center of an
elliptical galaxy. Millions of times the mass of the sun, the black hole
sucks in matter when it is actively accreting, and twin jets of light
and subatomic particles blast out from the poles along the axis of the
black holes rotation. One of the jets of blazar TXS 0506+056 points at
The connection of these jets to high-energy cosmic rays is of great
interest to us, said Gaisser, who comes from a distinguished line of
particle physicists at the Bartol Research Institute in the UD
Department of Physics and Astronomy.
The late Martin Pomerantz, Gaissers mentor and former Bartol
Institute director, pioneered astronomy and astrophysics research in
Antarctica. This harsh environment is an ideal place for such studies
because cosmic rays can enter at the poles unimpeded by Earths magnetic
Since they were first detected over one hundred years ago, cosmic
rayshighly energetic particles that continuously rain down on Earth
from spacehave posed an enduring mystery: Where do they come from?
Because cosmic rays are charged particles, their paths cannot be
traced directly back to their sources due to the strong magnetic fields
that fill space and warp their trajectories. But the powerful cosmic
accelerators that produce them may also produce neutrinos.
Neutrinos are uncharged particles, unaffected by even the most
powerful magnetic field. Because they rarely interact with matter and
have almost no masshence their sobriquet ghost particleneutrinos
travel nearly undisturbed from their accelerators, giving scientists an
almost direct pointer to their source.
The era of multimessenger astrophysics is here, said NSF Director
France C??rdova. Each messengerfrom electromagnetic radiation,
gravitational waves and now neutrinosgives us a more complete
understanding of the universe, and important new insights into the most
powerful objects and events in the sky. Such breakthroughs are only
possible through a long-term commitment to fundamental research and
investment in superb research facilities.
Spotting the highest energy neutrinos requires a massive particle
detector, and IceCube is by volume the worlds largest. Encompassing a
cubic kilometer of deep, pristine ice a mile beneath the surface at the
South Pole, the detector, which UD scientists helped build, is composed
of more than 5,000 light sensorson 86 cables on a grid with a spacing
more than the length of a football field.
When a neutrino interacts with the nucleus of an atom, it creates a
secondary charged particle, which, in turn, produces a characteristic
cone of blue light that is detected by IceCube and mapped through the
detectors grid of photomultiplier tubes. Because the charged particle
and light it creates stay essentially true to the neutrinos direction,
they give scientists a path to follow back to the source.
Following the Sept. 22 detection, the IceCube team quickly scoured
the detectors archival data and discovered a flare of over a dozen
astrophysical neutrinos detected in late 2014 and early 2015, coincident
with the same blazar, TXS 0506+056. This independent observation adds
to a growing body of data that indicates TXS 0506+056 is the first known
accelerator of the highest energy neutrinos and cosmic rays.
The IceCube Collaboration, with more than 300 scientists in 49
institutions from around the world, runs an extensive scientific program
that has established the foundations of neutrino astronomy. Their
research efforts, including critical contributions to the detector
operation, are funded by agencies in Australia, Belgium, Canada,
Denmark, Germany, Japan, New Zealand, Republic of Korea, Sweden,
Switzerland, the United Kingdom, and the United States.
by UD communications staff with material from the IceCube
Collaboration; photos and illustrations courtesy of South Pole Group,
Science magazine, IceCube/NASA