A New Map of the Universe, Painted With Cosmic Neutrinos

astro-marwil
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Topic 229734

Hallo!

See here.

Kind regards and happy crunching

Martin

Neal Burns
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I don't understand this part

I don't understand this part of the article.

Astrophysicists know that such energetic neutrinos could only arise when fast-moving atomic nuclei, known as cosmic rays, collide with material somewhere in space.

So creation of cosmic neutrinos is a 2-step process; first, an energetic source creates cosmic rays; second, the cosmic rays collide with material "somewhere in space," yielding cosmic neutrinos.

Where does step 2 happen? Near earth? Near the cosmic ray source? Or somewhere in between?

 

archae86
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Neal Burns wrote:Where does

Neal Burns wrote:
Where does step 2 happen? Near earth? Near the cosmic ray source? Or somewhere in between?

Everywhere that there is matter.  Once a neutrino is made, it is nearly as eternal as things get.  It just keeps cruising along hardly ever interacting with anything. 

As a young student at MIT, a problem set problem required us to estimate how many neutrinos made by the nearly MIT nuclear reactor passed through our bodies during a single lecture in room 26-100. (lots and lots)

The fact they interact so reluctantly explains why it is remarkably difficult to do neutrino detection.

 

 

Neal Burns
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archae86 wrote: Everywhere

archae86 wrote:

Everywhere that there is matter.  Once a neutrino is made, it is nearly as eternal as things get.  It just keeps cruising along hardly ever interacting with anything. 

 

There must be more to it than that. I'm running the CREDO app on my phone to detect cosmic rays by the muons they produce. This is clearly a more efficient way to monitor cosmic rays hitting the atmosphere than by looking for neutrinos.

 

Mike Hewson
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The original article is

The original article is behind a paywall, but the abstract of the article is as follows :

"The origin of high-energy cosmic rays, atomic nuclei that continuously impact Earth’s atmosphere, is unknown. Because of deflection by interstellar magnetic fields, cosmic rays produced within the Milky Way arrive at Earth from random directions. However, cosmic rays interact with matter near their sources and during propagation, which produces high-energy neutrinos. We searched for neutrino emission using machine learning techniques applied to 10 years of data from the IceCube Neutrino Observatory. By comparing diffuse emission models to a background-only hypothesis, we identified neutrino emission from the Galactic plane at the 4.5σ level of significance. The signal is consistent with diffuse emission of neutrinos from the Milky Way but could also arise from a population of unresolved point sources."

So the 'extra' neutrinos are a matter of modelling the whole data set and not especially identified detector interactions, hence assumptions about 'machine learning techniques', normal distribution etc. The usual 'gold standard' is 5 sigma for detections I believe eg.

n {\displaystyle p=F(\mu +n\sigma )-F(\mu -n\sigma )}  {\displaystyle {\text{i.e. }}1-p} {\displaystyle {\text{or }}1{\text{ in }}p}  
1 0.682689492137 0.317310507863
3 .15148718753
 
2 0.954499736104 0.045500263896
21 .9778945080
 
3 0.997300203937 0.002699796063
370 .398347345
 
4 0.999936657516 0.000063342484
15787 .1927673
5 0.999999426697 0.000000573303
1744277 .89362
6 0.999999998027 0.000000001973
506797345 .897

The above 'confidence levels' are equivalent to the natural language idea, for 5 sigma, that there is around one in 1.7 million chances that the values in the data set are due to merely random fluctuations as opposed to the specific hypothesis ( diffuse emission ). I'm not saying they haven't found a pattern, I'm just pointing out some of the mathematical meaning behind the claim.

As for "This is clearly a more efficient way to monitor cosmic rays hitting the atmosphere than by looking for neutrinos" : well no doubt that is true. But they have a neutrino detector and so will take advantage of the fact that neutrinos - being without electrical charge - will propagate without effects from the galaxy's magnetic field, say.

{ Bear in mind that neutrinos are really the theoretical way of balancing the books with regard to conservation theorems. However what few that are detected, out of the bazillions presumed to exist, do vary in direction as per known sources eg. nuclear reactors including the Sun. }

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Neal Burns
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 Thanks for your reply.

Thanks for your reply. The quote from the paper sounds a lot different than the magazine article.

I think what I'm going to take from this is that this group of researchers is using neutrinos to attempt to locate the high-energy processes that produce cosmic rays.

 

Neal

 

 

astro-marwil
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Hallo!"The original

Hallo!

"The original article is behind a paywall, but" you can download the preprint for free.

Kind regards and happy crunching

Martin

Mike Hewson
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Thanks for the link Martin,

Thanks for the link Martin, the abstract for that July 18 version is :

"The Galactic plane, harboring a diffuse neutrino flux, is a particularly interesting target to study potential cosmic-ray acceleration sites. Recent gamma-ray observations by HAWC and LHAASO have presented evidence for multiple Galactic sources that exhibit a spatially extended morphology and have energy spectra continuing beyond 100 TeV. A fraction of such emission could be produced by interactions of accelerated hadronic cosmic rays, resulting in an excess of high-energy neutrinos clustered near these regions. Using 10 years of IceCube data comprising track-like events that originate from charged-current muon neutrino interactions, we perform a dedicated search for extended neutrino sources in the Galaxy. We find no evidence for time-integrated neutrino emission from the potential extended sources studied in the Galactic plane. The most significant location, at 2.6σ post-trials, is a 1.7◦ sized region coincident with the unidentified TeV gamma-ray source 3HWC J1951+266. We provide strong constraints on hadronic emission from several regions in the Galaxy."

The Conclusions section notes that :

"We perform a targeted search for spatially extended neutrino emission in the Milky Way utilizing ten years of neutrino track-like events in IceCube. We focus on potential source extensions between 0.5 and 2.0 in a general scan across the Galactic plane and a catalog search with extended regions of TeV gamma-ray sources. The most significant location is a 1.7 region centered on the unidentified source 3HWC J1951+266 and is found to be inconsistent with the background-only hypothesis at 2.6σ after trials correction. We emphasize that this is still below our threshold for evidence of significant emission."

ie. they have found not much about not alot, which is probably quite an interesting outcome though. But this is hardly any Map Of The Universe, much less a new one as implied by the Quanta magazine article headline !

{ You are right Neal when you say "The quote from the paper sounds a lot different than the magazine article". I don't think anyone at Quanta read the article in detail. }

Cheers, Mike.

NB A sigma of 2.6 is around 1 in 100 chance of being fooled by random events that the source is real.

( edit ) In fact, as rightfully pointed out in comments to the article on the Quanta website, this statement in the first paragraph :

"But a smattering of the particles — those moving much faster than the rest — traveled here from powerful sources farther away."

.... is bollocks. The group of higher energy particles is what was studied. Their speed is :

  • equal to the speed of light if neutrinos are massless, or
  • so close to the speed of light that energy increases barely affect speed, if neutrinos have mass ( the likely case ).

Near the speed of light energy increases attract mainly an inertial penalty which you could call a mass increase. Either way none are moving much faster than the rest. This is sloppy wording at best.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Mike Hewson
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To illustrate what happens as

To illustrate what happens as you shove energy into a particle with non-zero rest mass :

.... a Newtonian analysis will give the green curve where speed will increase by any amount, without limit. The relativistic case is where there is an asymptotic approach to the speed of light, where for the TeV and PeV ranges a neutrino's velocity is just a tiny bit under the speed of light. Adding more energy at that stage merely makes it even harder to accelerate, so the velocity changes by a really tiny amount - and you can interpret that behaviour as an increase in the inertial mass of the neutrino.

The other confounding aspect of neutrinos is that a neutrino of a given (rest) mass may be considered* as a mixture of the three neutrino 'flavours' : electron flavour, muon flavour and tau flavour. There are three known neutrino mass states. The upshot is that when a given neutrino reaches a detector** it has a certain probability of reacting to produce an electron, another probability to produce a muon and yet another probability to produce a tau. If it reacts at all that is : most likely it will scoot right through a detector. The muon and the tau are heavier versions of the electron - same charge just more rest mass. This is all down to quantum mechanics and is the way the world works. To be even more confusing a given neutrino as it travels also changes it's flavour composition ... this is called oscillation ... but we'll leave it there.

Cheers, Mike.

* There is another way to view neutrino types, I've chosen what I think is the easiest to grasp.

** You never 'see' the neutrino, only the products from a given reaction. So if an electron was produced, say,  the Cherenkov radiation from that is what is registered. Cherenkov radiation is light emitted by a charged particle that is travelling faster than the speed of light for the medium it is traveling within, ice in this case. Note that light speed as an absolute limit refers to travelling in a vacuum.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Neal Burns
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Thanks for your thorough

Thanks for your thorough response.

While on the subject of neutrinos, is it possible to catch up to a neutrino? I've been watching some of the Fermilab Youtube videos on neutrinos. It sounds like they are created at one speed and are unable to ever slow down.

Neal

 

Mike Hewson
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Well if neutrinos have mass,

Well if neutrinos have mass, as observations appear to confirm, then yes you can catch up to one. You have to go faster and be in the band between a given neutrino's speed and that of light. You will gradually overtake it - if nothing else happens to you or it - though this may take quite some time to achieve ( but whose time ? ).

The speed of neutrinos has sort of been tested cosmically in that with Supernova 1987A the photons arrived just before the neutrinos, but further interpretation of this is limited by not knowing exactly when and where each began their flight to Earth.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

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