Neutrinos on Ice!
By Molly Michelson
How do scientists observe evidence of events outside of our solar system? Usually with telescopes collecting different wavelengths of light. But not always! Astrophysicists can use a variety of other tools to study the Universe—including a one-kilometer cube of ice buried a mile beneath the surface of Antarctica.
Neutrinos rarely interact with matter and the nearly massless subatomic particles can carry information about the workings of the highest-energy and most distant phenomena in the Universe. Every second, billions of neutrinos pass through every square centimeter of Earth (including you and me), but the vast majority originated in either in the Sun or in Earth’s atmosphere.
The rarer neutrinos, that is, those from the outer reaches of our galaxy or beyond, are what the scientists are hunting for. Theory suggests that neutrinos will be created in the same powerful objects where high-energy cosmic rays originate: supernovas, black holes, pulsars, and active galactic nuclei, for example. Observing neutrinos from such sources could provide insight into these exotic phenomena.
IceCube collected a year’s worth of data, recording a neutrino every six minutes. Upon analyzing the data, researchers originally concluded that the elusive interstellar neutrinos were absent. But as they combed through the data again, they detected two high-energy events, nicknaming them Bert and Ernie. Using the parameters to measure Bert and Ernie, the team has discovered 26 more neutrinos from beyond the Solar System, including ones named for Big Bird, Miss Piggy, and Snuffleupagus.
“From hints in earlier IceCube analyses, we have used improved analysis methods and more data to make a significant step forward in our search for the elusive astrophysical signal,” says team spokesperson Olga Botner, of Uppsala University. “We are now working hard on improving the significance of our observation, and on understanding what this signal means and where it comes from.”
“This is the first indication of very high-energy neutrinos coming from outside our solar system,” says Francis Halzen, of the University of Wisconsin-Madison and the principal investigator for IceCube. “It is gratifying to finally see what we have been looking for. This is the dawn of a new age of astronomy.”
What will these 28 neutrinos reveal about our universe? More than telescopes alone would tell us!
Their discovery is published in the recent edition of Science.
Image: Sven Lidstrom, IceCube/NSF