For the past few years, astronomers have been intensely studying gravitational waves. Gravitational waves have given astronomers a new model to see the universe with, yet a new discovery made in Antarctica may make the neutrino the new way of interpreting the universe.
Detection Of A Neutrino
A team of astronomers from around the world have located a source of neutrinos coming from points far off in the universe. Neutrinos are already hard to locate, but the newly found neutrino has come from a point in the universe where no neutrinos have ever been spotted before, approximately 4 billion light years away from Earth.
Two papers published in the journal Science detail how the international team of astronomers located a source of neutrinos emanating from around 4 billion years away from the planet, at a blazar called TXS 0506+056. A blazar is an extremely active galactic nucleus that has a relativistic jet (a jet that moves at nearly light speed) which is directed almost directly towards the Earth. TXS 0506+056 has a massive spinning black hole at the center which causes the galactic nucleus to shoot out twin particle jets.
The IceCube observatory, located at the South Pole detected an incoming high-energy neutrino during September of last year. The observatory has a sophisticated real-time alert system that notifies astronomers located around the world of the coordinates of the detection only 43 seconds after the neutrino is detected.
In response to the alert, 20 different observatories dialed in on the coordinates and attempted to pinpoint the origin of the neutrino. The astronomers found the blazar, which was shooting out gamma rays and neutrinos in the direction of the Earth. When archives of the IceCube’s data were analyzed, researchers were able to find more than a dozen different events associated with the object throughout the course of 2014 and 2015. This helped the researchers determine that the single high-energy neutrino detected last year was indeed from the blazar, which has a number of important implications for astronomy, according to Marcos Santander, astrophysicist from the University of Alabama. Santander explains the important of the discovery:
This is the first evidence that we have of an active galaxy emitting neutrinos, which means we may soon start observing the universe using neutrinos to learn more about these objects in ways that would be impossible with light alone.
The Ghost Particles
Not only was the detected neutrino the farthest neutrino ever detected thus far, it also provides astronomers with a great deal of information regarding cosmic rays. Astronomers have long known that cosmic rays bombard the Earth from space, but it has long been a mystery as to their origin. The trajectory of the cosmic rays gets altered quite a bit due to their nature as charged particles, which makes it difficult to discern their point of origin. However, neutrinos function as “ghost particles”, which react with matter infrequently due to the fact that they have almost no mass. This means it is quite likely that the ghost particle neutrinos traveled in, more or less, a straight line towards the Earth from TXS 0506+056, allowing their origin to be determined.
It’s important to note that IceCube doesn’t directly detect the neutrinos, rather it detects the rare interactions that neutrinos have with other molecules. Every once in a while one neutrino will hit into a larger particle and make it ramp up to speeds faster than the speed of light. When the speed of light is exceeded, the particles of matter that break the light speed limit shed many photons in response, which can then be detected with photon detectors. Scientists can then recreate the path of the neutrino.
How certain can scientists be that the blazar is indeed the source of the neutrino that was detected? The first study found that there was an approximately 1 in 1000 chance that the blazar isn’t the source of the neutrino, which is “the bare minimum needed to claim you’ve detected something”, according to astrophysicist Erin Bonning from Emory University (not involved in the study). Yet the first study is supported by the second study which compared previous observations of the TXS 0506+056 blazar with lower energy neutrinos that were detected by IceCube and this second study found that there was a better than 1 out of 1000 chance.
What Does The Discovery Mean?
High energy neutrinos are capable of revealing many of the mysteries behind objects like blazars. Azadeh Keivani from Penn State University explained that we are still just beginning to understand the physical mechanisms responsible for the acceleration of neutrinos to high energy states, but that he discovery of high-energy neutrinos from sources like blazars can “tell us about the origins of cosmics rays that produce them in particle interactions at the source.”
Since the time that gravitational waves were first discovered, they have been used to interpret and explains strange phenomena like neutron stars and merging black holes, which can’t be seen with traditional telescopes. Likewise, high energy neutrinos could peel back the curtain on mysteries events like the formation and evolution of galaxies or what happens within supermassive black holes.
Blazars are the most dominant figure within high-energy areas of the sky and have long been proposed as sources of neutrinos. The next move for the researchers will be to examine TXS 0506+056 and determine what circumstances make it and other blazars sources of neutrinos. Discerning the properties responsible for the generation of neutrinos can help researchers find more blazars like 0506+056 amongst the thousands of blazars currently known to emit gamma rays.
Researchers are already planning on making upgrades to IceCube’s sensors and detection equipment enabling it to hopefully pinpoint more sources of neutrinos. The upgrades will increase the volume of IceCube by approximately 10 times its current volume. There are also other gamma-ray observatories in the works, such as the Cherenkov Telescope Array, and it is hoped that the combination of the two systems will let more neutrino sources be detected more quickly.
The discovery of a reliable emitter of neutrinos may usher in a new era of astronomy, one where not only the objects of electromagnetic radiation can be studied, but other particles can be studied as well.