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!

I'd like to clarify for any laymen here: When they say "faster than light", they mean faster than the speed at which light travels in that particular medium, not faster than the speed of light in vacuum. It's a very important distinction to make. Given our current understanding of physical laws, nothing can exceed the speed of light in vacuum.

Edit: The original post has been edited to clarify that they meant "in ice".

Yes, there has been no evidence that anything can move faster than the speed of light in the vacuum. 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

A PHD student here, started my research career in MPhys on topic dark matter decay of astrophysical neutrino.(was based on ICECUBE results!)

1. Are you guys able to determine the flavour of the neutrino of this astrophysical neutrino from this blazar?
2. What was the expected energy of the astrophysical neutrino?
3. What is situation of 6.3PeV neutrino? Were we able to confirm this?
4. Something relating to my personal research. What is the progress of using Deep Learning methods in IceCube? in particular using DL for flavour classification - Is there anyone doing research on this?

A sincere Congratuations on achieving this amazing feat! Quite exciting to hear this news during the first hour of my birthday(Its 13th July where I am)!

1. The observed neutrinos in these analyses are muon neutrinos. IceCube Neutrino Observatory sees neutrinos through the light that is emitted by charged particles that are induced by the neutrino interaction with matter. In the case of the announced result these charged particles were muons that were produced by the muon neutrinos. Keep in mind that it does not mean the source has been producing muon neutrinos only. The neutrinos oscillate and can change flavor as they travel through the cosmos.
2. The astrophysical neutrinos that IceCube can see are in the range of 100 GeV to 10’s of PeVs. Basically, the expected neutrino energy depends on the source class that produces neutrinos. There are astrophysical neutrinos produced in Supernovae explosions that have lower energies of 100’s of MeV. There are other predicted class of astrophysical neutrinos from interaction of ultra high-energy cosmic rays that will have energies larger than 10 PeV.
3. Could you be more specific about 6.3 PeV neutrino? Are you referring to a reported event by IceCube?
4. Deep learning and Machine learning are the tools that has been used in some of IceCube's analyses. For instance, an ongoing analysis for Taus uses these techniques.

Thanks for you interest in IceCube and Happy Birthday!

-- AK

Hey IceCube! Congratulations on your huge result from us here at SNOLAB!

I suppose my question is this: what are the biggest questions in physics that can be studied with multi-messenger astronomy? What sort of direction do you think the field is heading?

NP / Focusing on the neutrino related multi-messenger astronomy, I think the biggest question we can answer is the origin of ultra high energy cosmic rays - where are they accelerated up to 10^21 eV energy - the acceleration mechanism, energetics, environment, and so on. (Note that, at this ultra high energy range, cosmic-rays we measure at the Earth are all hadronic -atomic nuclei.) As we gather more evidence in the future (with larger exposure , better detectors, continuous observation of multiwavelength EM (electromagnetic) observations on neutrino signals), we will learn which kind of astrophysical objects can produce high energy neutrinos and learn what kind of extreme environment can produce these highest energetic particles.

For the 5 year olds here... What kind of technologies could be developed from gaining understanding of Neutrinos?

IceCube’s main driver is basic science to understand the Universe.  I think my IceCube colleague Ignacio Taboada put it well: basic science is a very long term, very high risk, very high return investment in society.  In addition to the understanding of nature that basic science provides, it also drives technological breakthroughs that can be very practical to society.  The same photon sensor technology that was developed for particle physics experiments (including IceCube) is also used for PET scans to treat cancer and other diseases. — JV

Congrats guys, this is exciting!

So, we are sitting right now at the University of Toronto astronomy department, and two questions are coming up:

1) Why do you guys conflate cosmic rays with high energy neutrinos? Because one is a particle like a proton, and one is a fundamentally different particle. Isn't it a bit of a misnomer to conflate the two?

2) How is this unique from the SN 1987A detection of neutrinos? Tracing where it comes from in the sky more precisely?

Thanks!

Cosmic rays (charged particles including atomic nuclei) and neutrinos (charge-less particles) are distinct and very different particles, but they are closely related.  Detecting a neutrino from an astrophysical object is one of the few ways of identifying it as a cosmic-ray source.  The 1987A supernova detection was a great milestone in multi-messenger astronomy.  Those neutrinos were much lower energy (by a factor of 10 million!) and produced by different physics (thermal rather than particle physics). — JV

Any comments on the recent reports of the possibility of sterile neutrinos?

Do you think they exist? What would they mean for your research?

A previous IceCube search for sterile neutrinos constrained the allowed phase space for mass and mixing of the sterile neutrinos. IceCube analysis with more and recent data is in progress. While sterile neutrinos are an important possible piece of neutrino physics, they are not directly relevant to the results announced today. -- AK

Serrious Question: I'm not terribly familiar with this research project, why was the site for it selected in the antarctic? What advantages does that location in particular provide vs other locations?

Silly Question: Have you considered getting Icecube (rapper) and Neutrino (british mc) to do any publicity for your work?

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

Do you spend a significant amount of time in Antarctica? If so, what's it like? Pictures, stories, dispelling myths and misconceptions would be cool to hear.

I once applied for a NOAA scholarship and research program that included two years of living and researching the atmosphere down there. Didn't end up receiving it, but I always wonder what would have been if I had!

Edit: On, Wisconsin! (BS, Atmospheric & Oceanic Sciences / GIS, 2015)

Go Badgers!  Antarctica’s an amazing place.  It is protected by the international Antarctic Treaty as a unique continent for science, exploration, and art.  The summer season is short, so work during that season is intense, but we do try to take a break for holidays.  One of my favorite events there is the annual Christmas “race around the world” which is a combination footrace and parade with homemade floats.  New Year’s is also unique there, because you can celebrate every hour and in every time zone.  Another unique experience is having your eyelashes freeze: here’s a photo from when I was helping build IceCube: https://imgur.com/a/XB10cQY — JV

About how bright is the Cherenkov radiation that the detectors are looking for?

Are the detectors dispersed throughout the ice because I would have thought the light would get diffused and absorbed by the ice very quickly?

The Cherenkov radiation is very bright at the time of the flash. The challenge is that the duration of each flash is between a billionth and a millionth of a second. So if you were buried in the ice with the detector and had eyes with such good time resolution, you could see the flash. IceCube is in this ice because it is one of the largest blocks of crystal clear substance (of any material) on Earth. Each photon can travel for hundreds of feet before being absorbed. However, as you suggest, many of those photons do bounce around in the ice before being detected. We collaborate with glaciologists to understand the optical properties of the ice, both for neutrino astronomy and for climatology. — JV

We briefly saw a question from an IceCube alum who once proposed an alternate name for a neutrino detector: "What do you think? The Big Antarctic Telescope for Muon And Neutrinos....aka BATMAN!" But it disappeared before Justin Vandenbroucke could answer. What do you think, Justin?

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

What are the next steps for this research?

What's your favorite pancake topping?

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

What can this neutrino tell us about the universe?

Neutrinos were postulated over 80 years ago by Wolfgang Pauli in order to describe neutron decay. Without them the conservation of energy, one of the fundamental principles in physics, would have been broken. They are one of the most abundant elementary particles and yet least understood ones. Neutrinos interact rarely with other matter, traveling uninhibited through space, stars and Earth. Neutrinos contain information about their source and their physics at fundamental level. Due to these properties, neutrinos can reach us from the early Universe and from locations in the cosmos that no other particle can bring information from. -- AK

This discovery seems like it's more interesting in respect to cosmic rays than neutrino physics. Can we learn anything about neutrino oscillations or the mechanism that generates their masses from these very high energy neutrinos from very distant sources?

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

What's your favorite part about spending lots of time at Pole?

I had the privilege of working at the National Science Foundation's Amundsen-Scott South Pole Station during three seasons of IceCube construction.  My favorite part of it is the excitement of field work - working with your hands in an extreme environment to build a huge detector for a tiny particle.  The teamwork was a lot of fun and very satisfying - we worked really hard together and overcame challenges that arose on the spot.  Somehow every small joke in that location is much funnier than in the normal world.  My favorite was “Did you see the skier who arrived today?”. “Yeah, where did she come from?”  “North.” — JV

What kind of "background noise" is there 2000 meters under the south pole?

One of the reasons we constructed the detector so deep is that cosmic-ray muons from the atmosphere can reach from the atmosphere into the ice. However, the lower energy muons are absorbed by the ice, so the deeper you go the more this background noise decreases. Even at 2000 meters deep, we detect tens of billions of muons per year! Even though these particles are “background noise” for astrophysical neutrinos, we also do a lot of exciting science with those muons themselves. — JV

Is it found that neutrinos are only coming from very high energy sources like black holes and quasars or have you found any that came from something like a normal star?

The neutrino IceCube has detected is very high energy - over 100 TeV. (The X-ray machine a dentist uses is about 10,000,000,000 times lower energy, as a comparison). Normal stars like our Sun cannot produce particles this high in energy - the highest energy gamma-rays we have ever seen from our Sun may touch somewhere around only milion times higher than X-ray (and this is only very rare occasion). There may be other astrophysical objects that can produce these high energy particles. But, they will be likely more extreme environments than normal stars (such as deaths of very very massive stars). - NP

They travel faster than light? Does this means all the theories we have read till now needs to be amended? Do all the laws of nature we have now, needs to be reconsidered?

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

Does it ever frustrate you how elusive neutrinos are?

As in, my understanding is hundreds of billions pass through through myself every second. But detectors are lucky to catch a small handful in a year.

And if you have time, what sort of things do you during off hours at the South Pole?

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

Congratulations IceCube!

I see in your paper that your significance is 3.5 sigma right now. How long do we have to wait to reach 5 sigma from the same source? Is it a matter of time or do we need to seriously consider even larger scale neutrino telescopes in future?

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

Hello IceCube! Congratulations this is a big step forward.

My question is whether there is a physical motivation for the ‘neutrino burst’ that the legacy data search was based on. As in, what properties of the source dynamics could have caused the increased production of neutrinos in this extended period. Are their any hints in the optical data from other observatories that would suggest something special about this time period?

Thanks!

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

Apart from temperature, how does ANTARES/KM3NeT compare to IceCube in general? Are they able to cover the same areas of physics with comparable performance? Do you see them as "competitors" (like ATLAS v CMS, BaBar v Belle, LHCb v Belle II)?

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

How does a "high energy" neutrino get created? Can a neutrino be slowed down or sped up to make it higher/lower energy? Does it lose energy over distance like a photon due to cosmic expansion?

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

Do any of your findings provide support for sterile neutrinos models?

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

Apologies for what is probably a rather basic question. But you said that the charged particles the neutrinos produce in the ice travel faster than light, how is this possible?

Thank you for all the amazing work you do advancing the knowledge of the human race. Something I consider to be the highest of callings.

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

SNO/SNO+ alumni, it's been a while but what was your cost benefit analysis like on using a giant chunk of ice to capture neutrinos? Is the level of natural contamination from impurities in the ice or whatever lower than whatever liquid scintillator they're using now?

Also, congratulations!

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

Hi IceCube Team!

In addition to gravitational waves and electromagnetic radiation, neutrinos represent a new avenue for multimessenger astronomy. Are there currently any predicted signaling pathways of multi-messenger astronomy that have yet to be confirmed that your team is interested in looking at in the future?

Keep up the great work!!

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

Can you explain in layman's terms please. You catch a neutrino. How do you know with such precision which way it came from?

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

Congratulations on your Discovery!

I would like to ask what additional information about the Blazar could be derived from the Neutrino observations now and in future. Was there a Neutrino Source modelling employed as in the case of Gravitational Waves ?

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

Congrats to /u/hanavi and team! Can we look forward to continued ham radio contacts to KC4AAA at the antarctic station in the coming season?

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

Hi guys, fascinated by what you do at the observatory. A few questions.

How is Cherenkov radiation an implication of a neutrino? It is fascinating to me that this is how we can indirectly observe the presence of a neutrino, but how do we know the Cherenkov radiation isn’t produced by some other mechanism? Just curious, since as scientists we try to reduce the amount of variables as possible.

And also, I would like to know if you guys have openings for volunteers to help contribute to the research going on there. I am currently finishing my master’s in organic chemistry but originally got my bachelor’s in physics. Probably not of any use to you guys but I am eager to explore different projects in the natural sciences.

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

Congratulations, I'm so happy to hear that! Also, thank you for this opportunity!

I've been wondering about the detectors that are buried deep in the ice, are they safe enough? There seems to be a lot of pressure down there, so can't anything happen to them this far below the surface?

If I'm correct, the holes were drilled by melting the ice so that the openings above the detectors could freeze and close later on, but does that leave any way of checking/saving the detectors in case of trouble?

Thank you in advance.

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

Something I've been curious about for ages: Can cosmic rays be harnessed as a source of energy? Why or why not?

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