What Are Ghost Particles? And Why Are They So Important?

Many of us may never witness ghosts directly, yet trillions of them pass through our bodies daily - the invisible cosmic particles known as neutrinos that slip effortlessly through almost everything have earned them the moniker "ghost particles."

Photo by David Kopacz

Neutrinos are also crucial to understanding our universe; recently, scientists used neutrinos to track supernovae, black holes and other phenomena associated with space travel.

What Are Ghost Particles?

Neutrinos are among the trickiest particles in nature, barely interacting with matter and therefore making detection almost impossible. But physicists have learned that neutrinos play an invaluable role in probing astrophysical phenomena and deepening our understanding of particle interactions.

At Hokkaido University, researchers believe that understanding how neutrinos form could provide us with greater insights into our Universe as a whole.

Astronomers recently discovered a way to use neutrinos as a powerful tool in investigating cosmic rays - high-energy particles which rain down from space - known as cosmic rays. A specific type of neutrino can act like a "smoking gun" to locate their source; researchers believe blazars may act as natural space factories where cosmic rays form.

Gaisser and his colleagues at UD's Bartol Research Institute have installed a network of detectors in Antarctica to search for neutrinos - subatomic particles with as much mass as an atom but traveling at almost light speed across vast distances. Last year, they observed an unusual type of neutrino coming from the same direction as jet of particles being expelled by one of these blazars; such an observation suggests these neutrinos act as direct and unaltered representatives for high-energy cosmic rays.

What Are Neutrinos?

Neutrinos are among the most abundant particles in our universe, yet are exceedingly difficult to detect due to their non-interactance with matter. Yet their presence provides insight into physicists' attempts at unraveling many mysteries.

William & Mary scientists led by William & Mary physicist Dr. Matthew Jones recently made the most significant detection yet of high-energy neutrinos in our galaxy, providing evidence for its existence as well as insight into how dark matter influences galaxies and cosmic structures generally.

These results were made possible thanks to an international research collaboration involving thousands of networked sensors buried deep within a cubic kilometer of Antarctic ice, known as the IceCube Neutrino Observatory at NSF's Amundsen-Scott South Pole Station. This massive detector consists of 79 "strings" of sensors each housing 60 sensors embedded more than one mile into the ice. Sensors use their light detectors to observe faint patterns created when neutrinos strike the surface and decay into energy particles, looking out for light patterns produced when neutrinos collimate with materialized energy in order to observe results that come back out later on from impacts or decay events.

IceCube observatory's sensors, as with those found elsewhere (such as at the bottom of the ocean), are buried underground to avoid interference from electromagnetic radiation from above and contamination by air-born pollutants, both of which could potentially compromise measurements being made at these polar regions.

Why Are Neutrinos Important?

Neutrinos are unlike ordinary matter in that they're massless and non-interacting particles; every second billions pass us without us even realizing it. Neutrinos can be produced in nuclear reactors, released during radioactive element decay or produced at extreme cosmic events like supermassive black holes or exploding stars; they were even around at the Big Bang itself! But due to their limited interaction with other particles, neutrinos can be difficult to detect; to capture them physicists have constructed giant detectors in gold/nickel mines, tunnels beneath mountains, ocean waters and Antarctic ice ice to detect neutrinos.

Neutrinos may help us unravel some of the Universe's mysteries, such as why there is an excess of matter but not antimatter (its oppositely charged counterpart), in our galaxy and other galaxies across our universe. They could also provide answers to why there appears to be invisible material which doesn't interact with visible matter (known as dark matter problem).

Scientists at PNNL and elsewhere are searching for these elusive ghost particles because once discovered they can provide insight into what occurred in the Universe billions of years ago and help solve puzzles about cataclysmic cosmic events which generate neutrinos and cosmic rays hurled through our atmosphere at near light speed.

How Are Neutrinos Detected?

Neutrinos differ from other cosmic particles by possessing no electrical charge and passing straight through Earth and other matter without altering; hence their nickname as ghost particles by scientists.

Neutrinos can be difficult to detect, yet their trails can leave visible evidence in water or ice. Researchers need sensitive detectors like the IceCube Neutrino Observatory buried deep within Antarctica ice for this task; in particular, scientists have used it to assemble an image of our Milky Way galaxy made entirely with particles rather than electromagnetic energy.

This neutrino-based image illustrates the source of thousands of invisible "ghost particles", or neutrinos, that exist but usually pass unnoticed through Earth's atmosphere. The result is an unparalleled galactic snapshot, depicting exactly which regions produce such particles (such as supernovae) within our galaxy.

IceCube's successor, Trident, can detect neutrinos from billions of light years away; but physicists also hope to be able to detect those created closer to Earth from nuclear reactors - an ongoing challenge which will be met through construction of a neutrino detector facility that's over 100 times bigger than IceCube in South Dakota.