Andrew Griffin: Ghost particle from deep in space could change our understanding of the universe
Scientists have been
mystified by cosmic rays since they were found more than a century ago, pouring
down onto Earth. Despite their huge number and intense power, it has been
unclear where they come from. The new discovery could finally explain
where cosmic rays originate. If correct, the answer would be a fittingly
spectacular phenomenon deep in the universe. The neutrinos appear
to be spewing out of fast spinning supermassive black holes and the discovery
could give us an entirely new way of looking at the universe. The particles
might be a “third messenger” carrying energy from elsewhere in the cosmos,
in addition to light and gravitational waves.
If so, the newly
observed particle would be an unprecedented new way of understanding
some of the most intense and mysterious phenomena in the universe. Neutrinos
could be doubly helpful because they have no mass and travel in an almost
entirely straight line through the universe – which makes them very difficult
to detect but very easy to track, as they travel billions of light years. “Neutrinos rarely
interact with matter,” said Professor Paul O’Brien, a member of the
international team of astronomers at the University of Leicester. “To detect
them at all from the cosmos is amazing, but to have a possible source
identified is a triumph. “This result will allow us to study the most distant, powerful
energy sources in the universe in a completely new way.”
The discovery was
reported in two new papers published in the journal Science, and
was the result of work by a huge global team of researchers. “These
intriguing results also represent the remarkable culmination of thousands of
human years [worth] of intensive activities by the IceCube Collaboration, to
bring the dream of neutrino astronomy to reality,” said Darren Grant, a
professor of physics at the University of Alberta, and spokesman of the IceCube
Collaboration, an international team with more than 300 scientists in 12
countries.
The neutrino was found
on September 22 by the IceCube observatory, a huge facility a mile beneath the
South Pole. A grid of more than 5,000 super sensitive sensors picked up the
characteristic blue “Cherenkov” light emitted as the neutrino interacted with ice.
Having almost no mass and passing right through planets, stars and anything
else in its way, the particle travelled in a straight line from its point of
origin to Earth. As a result, astronomers were able to track its trajectory
back across billions of light years to its probable source.
News of the detection
sent astronomers into a frenzy as telescopes were pointed in the suggested
direction. The search led to a “blazar”, a special class of galaxy containing a
supermassive black hole four billion light years away, just to the left of the
constellation Orion. The finding was the
result of a global effort to track down the source, triggered by an automated
alert after the intriguing detection at the South Pole. “This result really
highlights the importance of taking a multimessenger approach to these
searches,” said Erik Blaufuss, a research scientist in the UMD Department of
Physics who led the effort – over several years – to create and deploy
IceCube’s high energy event alert system. “Any one observation made alone would
likely not have let us piece together what is actually going on inside this
source.”
A key feature of
blazars is twin jets of light and elementary particles that shoot from the
poles of the swirling whirlwind of material surrounding the black hole. One of
those jets happened to point towards Earth and led to one of the most profound
discoveries in the history of astrophysics. The neutrino detected by IceCube is
thought to have been created by high energy cosmic rays from the jets interacting
with nearby material. Unlike high energy neutrinos, most cosmic rays carry an
electric charge that causes their trajectories to be warped by magnetic fields,
making it impossible to trace their origins. By contrast, neutrinos are
unaffected by even the most powerful magnetic fields.
The blazar believed to
have generated the neutrino – codenamed TXS 0506 + 056 – was located in less
than a minute, after the IceCube team relayed coordinates for follow-up
observations to telescopes worldwide. Being able to detect high energy
neutrinos will provide yet another window on the universe, say the
scientists. The sensational discovery of the second “messenger”, gravitational
waves – ripples in space-time – was announced in February 2016.
France Cordova,
director of the US National Science Foundation (NSF), that manages the IceCube
laboratory, said: “The era of multimessenger astrophysics is here. “Each
messenger, from electro-magnetic radiation [to] gravitational waves, and now
neutrinos, gives us a more complete under-standing of the universe and important
new insights into the most powerful objects and events in the sky.” Cosmic rays
were discovered in 1912 by physicist Victor Hess, using instruments on a
balloon flight. Later research showed them to be made of protons,
electrons or atomic nuclei accelerated to speeds approaching that of light.
