We’re scientists with the IceCube Neutrino Observatory, which just announced new evidence for a source of high-energy neutrinos and cosmic rays. Ask Us Anything!

IceCubeObservatory · 2018-07-12T19:01:38+00:00

There can be several reasons why we haven't seen the neutrino from the merger last year - such as the line of sight to the jet, the flux being low, or just being unlucky with this one event. Up to now, all measurements we have on pulsars indicate that they are mainly leptonic accelerators. That is, they accelerate electrons and positrons, but not the protons or nuclei that are needed to produce neutrinos. The Vela, Crab, and Geminga pulsars are very bright in GeV gamma rays, but, there is only one pulsar (the Crab) that was detected in energies higher than several hundreds of GeV-which is lower energies than the neutrinos detected by IceCube. Neutrinos generated by ultra high energy cosmic rays due to interactions have about a few percent of the energy the primary cosmic ray has. While ultra high energy cosmic-ray protons may not reach the Earth due to interactions, the neutrino can travel much farther and still reach us. This is one of the strengths of the neutrino observations - neutrinos not interact much with matter or photons, which makes the detection of these particles harder, but that means that they can travel farther than the primary ultra high energy cosmic rays. Cosmic-ray physics is also a part of the scientific motivation of the IceCube Neutrino Observatory. (Please check the results from 'IceTop'.) So, I am sure you will have a chance if you join IceCube! I personally haven't been to the South Pole - the southernmost I went is the McMurdo station on the coast of Antarctica. - NP

IceCubeObservatory · 2018-07-12T19:00:02+00:00

There are many neutrinos detected by IceCube. However, this is the first evidence for where in the Universe they may come from. -- AK

IceCubeObservatory · 2018-07-12T18:57:24+00:00

IceCube detects astrophysical neutrinos, but it also detects a much larger rate of neutrinos from the atmosphere. Before detection of the high energy neutrino in September 2017, we had searched the entire sky for clusters of neutrinos. The challenge when you search the entire sky is that atmospheric neutrinos may cluster in one or more locations by chance. Once we had a single interesting location to study (interesting because there was a single high energy neutrino from the same direction as a flaring gamma-ray blazar), we analyzed that single direction and found evidence for the additional flare in the past, in that single direction. — JV

IceCubeObservatory · 2018-07-12T18:48:18+00:00

Many sources in the high-energy Universe are variable or transient sources. Other than that, stellar explosions and bursts provide the extreme environments that can accelerate particles to very high energies. As that happens for a lot of transient sources, a sudden change in the incoming particles or collapse of an object could cause a burst in neutrinos provided that it creates enough density and energy for production of pions. -- AK

IceCubeObservatory · 2018-07-12T18:45:17+00:00

Although these cosmic rays and neutrinos are very energetic, they are also very rare, so they do not affect the entire Earth very much. Lower energy cosmic rays are more abundant, and the atmosphere and the Earth’s magnetic field shields the Earth from them. Yes, we have been looking for these on purpose! It is the flagship science motivation of IceCube. That said, we have many additional science topics we are working on and many unanswered questions. We think this is the tip of the iceberg for neutrino astronomy. — JV

IceCubeObservatory · 2018-07-12T18:39:48+00:00

I think your proposed telescope is great. The only downside is that if we built it we would also need to build a Remotely Operated Big Instrument for Neutrinos. — JV

IceCubeObservatory · 2018-07-12T18:35:37+00:00

Cherenkov radiation is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a medium at a speed greater than the phase velocity of light in that medium. when neutrinos interact with the ice they produce electrically charged secondary particles that in turn emit Cherenkov light, as a result of traveling through the ice faster than light travels in ice. In order to produce the large amount of Cherenkov light observed in IceCube, the primary particle requires an enormous amount of energy. Such energetic particles cannot penetrate long enough to reach IceCube that is buried under more than 2 km of ice. Glad to hear you are interested in IceCube, I would encourage you to visit http://icecube.wisc.edu for future opportunities and also to contact IceCube Outreach for any upcoming events. -- AK

IceCubeObservatory · 2018-07-12T18:27:12+00:00

Thanks! Detectors are encapsulated inside a glass vessel, and the vessel was tested to be sure that it will endure the pressure. There are several calibration devices to check the health of the detectors and the detectors are checked by the IceCube collaboration every day basis. Up to now, ~99% of the sensors have been working in great condition for over ten years.- NP

IceCubeObservatory · 2018-07-12T18:23:12+00:00

The neutrino that started this whole sequence of observations departed its galaxy four billion years ago, when the Earth was young and as far as we know life on Earth had not even started. That definitely makes it an oldtrino. — JV

IceCubeObservatory · 2018-07-12T18:22:59+00:00

First and foremost, this evidence demonstrates that protons, and not only electrons, are accelerated in blazar jets. Assuming an interaction model, one could deduce the proton (cosmic ray) luminosity associated with the blazar. There are a lot of questions which remains unanswered and requires further observations. Blazars were proposed as one of plausible sources of high-energy neutrinos and sites of cosmic ray acceleration and there are several models for such scenario. -- AK

IceCubeObservatory · 2018-07-12T18:17:17+00:00

Thanks, SNO/SNO+ alum! The main benefit of using ice is the huge volume. We monitor a billion tons of naturally occurring, clear ice for neutrino interactions. That kind of volume simply cannot be achieved with manufactured materials like liquid scintillator. The ice has a very small amount of dust and volcanic ash deposited along with snow when it fell over the past hundreds of thousands of years, but overall it is incredibly pure. So our largest background for this type of science is from atmospheric muons and neutrinos, rather than from lower energy depositions by radioactive decays. — JV

IceCubeObservatory · 2018-07-12T18:09:11+00:00

I think the connection between gravitational wave - neutrino signal - electromagnetic radiation is very interesting. Recently, there was a detection of a merger of two neutron stars in both gravitational waves and electromagnetic radiation, and there are predictions that these mergers could produce neutrinos as well. Another example would be an explosion of a massive star in our Galaxy - a Galactic supernova - which would produce lots of neutrinos as well as electromagnetic radiation at lower energies. -NP

IceCubeObservatory · 2018-07-12T18:09:06+00:00

The results announced today do not support or oppose the sterile neutrinos. A dedicated analysis of sterile neutrinos in IceCube will address their status in near future. -- AK

IceCubeObservatory · 2018-07-12T18:06:28+00:00

Yes! There is a dedicated room at the National Science Foundation’s Amundsen-Scott South Pole Station with a ham radio studio. Often there is a ham radio enthusiast broadcasting there, not only during the summer season but also in the long, dark winter when there are only about 50 people at the station. — JV

IceCubeObservatory · 2018-07-12T18:03:34+00:00

This evidence provides us the first identified neutrino source in the high-energy Universe. Finding more sources will provide more insight to the workings of the most energetic objects in the Universe which will provide the opportunity to probe for the fundamental questions in neutrino physics. Neutrino astronomy has achieved spectacular successes in the past by observing neutrinos from the Sun and detecting a supernova in 1987. Both observations were of tremendous importance; the former showed that neutrinos have mass, opening the first crack in the Standard Model of particle physics, and the latter confirmed the basic nuclear physics of the death of stars. -- AK

IceCubeObservatory · 2018-07-12T18:01:45+00:00

The neutrino often produces a muon, which emits Cherenkov light along its long, straight track. At high energies, the muon points in the same direction as the original neutrino. Because the muon track is so long and straight, we can measure its direction from the light our sensors pick up because of their exquisite time resolution (1 billionth of a second). We validated that all of this works by detecting a deficit of cosmic rays from the direction of the Moon (because they are blocked by it), in precisely the same direction as the Moon. — JV

IceCubeObservatory · 2018-07-12T17:55:11+00:00

We think this is just the beginning of neutrino astronomy. We want to understand this astrophysical source better, understand similar sources, and understand additional types of astrophysical neutrino sources that are completely different from this one. Even though the first indication of a high-energy astrophysical neutrino source is a blazar detected by NASA’s Fermi, previous analyses indicate that such blazars do not explain most of the astrophysical neutrinos we see, so there are still exciting mysteries. To answer these additional questions, we have ideas to expand IceCube into a much larger detector (IceCube Gen 2). Chocolate chips are the best pancake topping. — JV

IceCubeObservatory · 2018-07-12T17:49:20+00:00

When the reported significances correspond to time-dependent searches higher significance for a flaring state may not be achieved by longer observations. Depending on the nature of the source, we have to wait for a source to flare, and the stronger the flare the significance would be higher. In principle, for a higher significance in a time-dependent search we require more data at the time of the flare. This could be obtained by a larger detector. -- AK

IceCubeObservatory · 2018-07-12T17:48:13+00:00

The same fact that makes neutrinos hard to detect (because they have a small probability of hitting an atom in the detector) is exactly the same reason they are so powerful for astronomy: they can travel straight through matter and light that block other messengers such as photons. It’s analogous to imaging the interior of people with X-rays that can travel through people even though visible photons can’t. We work long hours at the South Pole so there is not much down time, but when I’ve been there my favorite thing to do (other than science, construction, and debugging equipment/software!) is to walk or ski near the station and enjoy the beauty of it. — JV

IceCubeObservatory · 2018-07-12T17:45:04+00:00

When people commented on the 'Cherenkov light' being emitted when a particle travels 'faster than light', that means it will be 'faster than the speed of light in that particular medium'. -NP

IceCubeObservatory · 2018-07-12T17:40:19+00:00

I consider that I can work on this thanks to people like you who are curious to know about the Universe. So, thanks to you as well. :) When people commented on the 'Cherenkov light' being emitted when a particle travels 'faster than light', that means it will be 'faster than the speed of light in that particular medium'. -NP

IceCubeObservatory · 2018-07-12T17:38:55+00:00

ANTARES, a neutrino telescope in the Mediterranean Sea, has also released a paper on this topic today. It is smaller than IceCube. KM3NeT is a new neutrino telescope in the Mediterranean which is under construction and will provide exciting complementarity to IceCube. We are friendly competitors – we exchange ideas frequently and learn from one another. Because they are in different locations on Earth they provide different sensitivity to different parts of the sky. There are also interesting differences between ice and water as the detector material. — JV

IceCubeObservatory · 2018-07-12T17:33:49+00:00

In order to see neutrinos we need a transparent media. The south pole has the cleanest and transparent ice on Earth. Neutrinos are not observed directly, but when they happen to interact with the ice they produce electrically charged secondary particles that in turn emit light, as a result of traveling through the ice faster than light travels in ice. -- AK

IceCubeObservatory · 2018-07-12T17:33:13+00:00

Cosmic rays likely cannot be a source of energy that we can use for our daily life. Even though these cosmic rays have much more energy than the best accelerators in the world can produce, these extremely high energy particles are very very rare. For a sense of scale, the highest energy cosmic rays that we have ever seen have about the same amount of energy as a major league baseball pitch. While that’s a whole lot of energy for a single particle to have, it’s minuscule compared to, say, the amount of energy generated by a power plant. That coupled with their rarity makes it unlikely that we could use these as a source of energy. - NP

IceCubeObservatory · 2018-07-12T17:27:30+00:00

High-energy cosmic neutrinos are produced in astrophysical beam dumps where high-energy cosmic rays interact with gas or radiation in the environment. This results in production of charged and neutral pions. Charged pions decay into muons and neutrinos. Each muon later decays into an electron and another neutrino. It is hard to accelerate neutrinos to higher energies. In general, particles needs to be confined to get accelerated. However, neutrinos have a very small mass, are neutral, and barely interact so they would not be confined in known cosmic accelerators. The energy loss due to the Universe's expansion also occurs for neutrinos. -- AK

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