Firming up on earlier results using data that they collected between 2010 and 2012, scientists at the IceCube neutrino observatory revealed that they had indeed detected extragalactic neutrinos.
The IceCube observatory is made up of instrumentation lodged within a cubic kilometre of ice in the Antarctic and is designed to detect neutrinos of even very high energies which can exceed those produced in accelerators such as the LHC by a factor of more than a million. The research was reported recently in the journal Physical Review Letters.
The present results reaffirm the conclusions drawn from analysis published last year, and they are derived from a different technique. The present study traces out the muons released due to rare neutrino collisions and which, in turn, leave a trail of light that mirror the trajectory of the neutrino.
The neutrinos sampled have energy which matches that of neutrinos detected when sampling the sky of the South Pole. According to Albrecht Karle, a senior author of the study, there is very strong evidence that a sizeable fraction of the neutrinos detected are extragalactic. He added, in an email to this correspondent: “All this in itself may not need to be seen as firm proof. For example, it has been suggested that such events could originate from a dark matter halo in our galaxy. If such dark matter consists of certain particles, such as WIMPs (weakly interacting massive particles) it may decay into energetic neutrinos. Such a dark matter distribution would be relatively isotropic, too. However it seems far fetched and not very well motivated at this time.”
Very high energy neutrinos are created deep inside violent astrophysical events far away in the universe. Since the neutrinos hardly react with matter on the way to the earth, they hold pristine information of the sources where they were born. Such neutrinos may in the future be used to develop the science of neutrino astronomy. In addition, studying them may reveal how nature creates powerful accelerators in the cosmos.
The observations were made by pointing the IceCube Observatory, composed of thousands of detectors placed beneath the Antarctic ice at the South Pole, towards the Northern Hemisphere.
Neutrinos coming in from that direction and filtered by the thickness of the Earth were detected. In the two years from May 2010 to May 2012, nearly 35,000 events were recorded of which only about 20 were due to neutrinos of such high energies as to come from astrophysical sources.
