A single ghost-like subatomic particle captured on Earth could finally help solve a cosmic mystery that has left scientists baffled for more than a century.
The high energy neutrino – the first of its type ever detected – was traced four billion light years to its source, a distant elliptical galaxy with a giant black hole at its heart emitting jets of light and radiation aimed directly at Earth.
Known as a ‘blazar’, this galaxy was the smoking gun that led astronomers to finally unravel the 100 year-old riddle around the origin of high energy cosmic rays.
An artist’s impression of the active galactic nucleus where the ghost-like subatomic particle captured at the IceCube laboratory likely originated
These rays, which consist of fast-moving elementary particles, pepper Earth from space and pose a threat to astronauts, as well as the crews and passengers of commercial flights.
Discovering the ghost-like particle, which burst from the ‘blazar’ before the Earth formed, could provide an entirely new way of looking at the cosmos, scientists claim.
The neutrino discovery, published in the journal Science, points towards one likely origin – powerful jets of accelerated particles fired from the poles of rapidly rotating supermassive black holes.
Until now, the origin of high energy cosmic rays was a mystery to scientists.
Beyond cosmic rays, the latest finding could provide a new way of peering into the depths of the universe.
Like the discovery of gravitational waves in 2016, neutrinos could be a new ‘messenger’, carrying energy across the cosmos.
Neutrinos are the so-called ‘third messenger’, following light protons and gravitational waves.
The high-energy neutrino was first detected on September 22, 2017 by the IceCube observatory, a huge facility sunk a mile beneath the South Pole.
Here, a grid of more than 5,000 super-sensitive sensors picked up the characteristic blue ‘Cherenkov’ light emitted as the neutrino interacted with the 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.
The IceCube laboratory at the South Pole – the largest neutrino observatory in the world – where scientists made the first ever detection of a high-energy neutrino
News of the detection sent astronomers into a frenzy of activity as telescopes were quickly pointed in the suggested direction.
The search led to the discovery of a ‘blazar’, a special class of galaxy containing a supermassive black hole four billion light years away, left of the Orion constellation.
A key feature of blazars is twin jets of light and elementary particles shooting from the poles of the swirling mass of material surrounding the black hole.
The neutrino detected by IceCube is thought to have been created by high-energy cosmic rays from the jets interacting with nearby material.
Professor Paul O’Brien, a member of the international team of astronomers from the University of Leicester, said: ‘Neutrinos rarely interact with matter.
‘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.’
WHAT IS A HIGH-ENERGY NEUTRINO?
High-energy neutrinos are chargeless, massless subatomic particles.
Neutrinos are one of the fundamental particles that make up the universe, but are some of the least understood as they interact very weakly with everything around them.
This makes them ideal astronomical messengers, since they can through the universe without scattering, absorption or deflection.
However, these weak interactions also makes the particles notoriously tough to detect, leading to neutrino observatories requiring large-scale detectors.
The only time they interact with other particles is when they collide head on.
Most neutrino detectors use vast underground tanks brimming with water and fitted with extremely-sensitive sensors to capture brief flashes of light emitted when a neutrino smashes into a particle within the fluid.
However, the largest neutrino observatory in the world, IceCube, instead uses a kilometre-sized section of ice some 1.55 miles (2.5 kilometres) beneath the surface of Antarctica, close to the South Pole.
Sensors are embedded deep into the ice to capture the brief flashes that occur when neutrinos collide with particles in the ice.
Capturing evidence of these collisions does not occur often, but when it does, it sets off a chain of events at the observatory to try and determine where the neutrino originated.
Most neutrinos come from the sun or cosmic rays striking our atmosphere.
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.
In contrast, neutrinos are unaffected by even the most powerful magnetic fields.
The blazar believed to have generated the neutrino, code-named TXS 0506 + 056, was located in less than a minute after the IceCube team relayed co-ordinates for follow-up observations to telescopes worldwide.
Being able to detect high-energy neutrinos will provide yet another window on the universe, said the scientists.
The IceCube array uses strings of sensors which are lowered down boreholes in the ice. The IceTop has two layers of detectors beneath the surface. The Eiffel Tower is depicted, bottom right, to show the scale of the detector
The sensational discovery of the second ‘messenger’, gravitational waves, or 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 multi-messenger astrophysics is here.
‘Each messenger, from electromagnetic radiation, gravitational waves and now neutrinos, gives us a more complete understanding 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 up of protons, electrons or atomic nuclei accelerated to speeds approaching that of light.
HOW DOES THE ICECUBE WORK?
IceCube is the world’s most sensitive neutrino telescope.
IceCube is a neutrino detector composed of 5,160 optical modules embedded in a gigaton of crystal-clear ice a mile beneath the geographic South Pole.
Supported by the National Science Foundation, IceCube is capable of capturing the fleeting signatures of high-energy neutrinos — nearly massless particles generated, presumably, by dense, violent objects such as supermassive black holes, galaxy clusters, and the energetic cores of star-forming galaxies.
The IceCube lab on the Antarctic tundra near the US Amundsen-Scott South Pole Station. Scientists have been building the observatory for the past five years
The size of the observatory – a cubic kilometre of ice – is important because it increases the number of potential collisions that can be observed.
In addition, the type of ice at the South Pole is perfect for detecting the rare collisions. Most ice contains air bubbles and other pockets that would distort measurements.
But at the South Pole, it’s basically a giant glacier consisting almost entirely of water ice, meaning there are more atoms and so more chance of a neutrino collision.
Each of the round detectors are placed on a long string and lowered into holes in the ice that were drilled using a powerful hot-water drill that melted up to 200,000 gallons of ice per hole.
The final module, signed by all the team, is readied for deployment
Each cable string has 60 sensors at depth with 86 strings making up the main IceCube detector.
The giant telescope was built at an average depth of up to 8,000 feet beneath the Antarctic plateau at the South Pole.
The entire project cost $279 million, of which the National Science Foundation contributed $242 million towards it.
The final stretch of construction ended with the drilling of the last of 86 holes for the 5,160 optical sensors that are now installed to form the main detector.
The collision between a neutrino and an atom produces particles known as ‘muons’ in a flash of blue light called ‘Cherenkov radiation’. In the ultratransparency of the Antarctic ice, IceCube’s optical sensors detect this blue light.
The trail left in the wake of the subatomic collision allows scientists to trace the direction of the incoming neutrino, back to its point of origin, be it a black hole or a crashing galaxy.