This allows them to carry valuable information across the entire universe. The reason that cosmic neutrinos are important is the same reason that neutrinos themselves are so frustrating to measure: they ignore almost everything. That works out to be about a tenth of a millijoule, which is a lot for a particle that has an effective size of nearly zero, and it is about equivalent to the kinetic energy of a thousand flying mosquitoes, in case that horrific unit of measurement is of any help to you. As you might expect, the resulting neutrinos have stupendously high energies themselves: a million billion electronvolts (1 petaelectronvolt) or so. We're talking events like supernova remnant shocks, active galactic nuclei jets, and gamma-ray bursts, which can emit as much energy in a few seconds as our sun does over ten billion years. Cosmic NeutrinosĬosmic neutrinos are born, we think, in the same sorts of ultra high energy events out in the universe that also generate gamma rays and cosmic rays. These are called cosmic neutrinos, or astrophysical neutrinos. (This happens a lot.) What's much rarer to see are neutrinos that aren't produced close to home-neutrinos that come from outside of our solar system, and even outside of our galaxy. The most common source for the neutrinos that we see here on Earth is the sun, which produces an electron neutrino every time two protons fuse into deuterium. To take one common example, protons and neutrons colliding with each other create pions, which are subatomic particles that decay into a mix of muon and electron neutrinos. The original flavor that each neutrino takes depends on how it was created: most often, neutrinos are created through high energy nuclear processes like you'd find going on inside stars. Each flavor has a slightly different (but tiny) mass, on the order of a million times smaller than the mass of a single electron, and a neutrino can oscillate between these three flavors as it zips along. We’re pretty sure that neutrinos come in three different (but equally tasty) flavors: electron, muon, and tau. Fortunately, the enormous number of neutrinos that are flying through everything all the time compensates for the low probability of collision, and that has allowed us to learn some things about these elusive particles. The only way to bring a neutrino to a halt is if it runs smack into an electron or the nucleus of an atom, but this is ridiculously improbable: you'd need a piece of lead about a light year long to be reasonably sure catching any one specific neutrino. Some 65 billion solar neutrinos just passed through every square centimeter of your body, and if you wait a second, 65 billion more of them will do it again. Since they're small, fast, and charge-free, they aren't affected by nuisances like electromagnetic fields, meaning that they can pass unmolested through rather a lot of pretty much anything. Neutrinos are elementary particles (like quarks, photons, and the Higgs boson) that have no charge and virtually no mass. (Go here for the incredible story of the engineering of the detector, called IceCube.) What are Neutrinos? But the few we've seen have energies up to a thousand times greater than what the Large Hadron Collider can generate, and we're just starting to be able to get a sense of where they might be coming from. These particles are nearly impossible to detect-it took a specially designed system of sensors burried in a cubic kilometer of ice. In a research published last week in Physical Review Letters, an Antarctic detector has managed to confirm the existence of a small handful of cosmic neutrinos: ultra high energy particles that likely originated from unknown sources far outside of our galaxy.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |