[HN Gopher] Physicists produce neutrino images of Milky Way galaxy ___________________________________________________________________ Physicists produce neutrino images of Milky Way galaxy Author : _Microft Score : 70 points Date : 2023-06-29 19:22 UTC (3 hours ago) (HTM) web link (drexel.edu) (TXT) w3m dump (drexel.edu) | oblib wrote: | This link is to the image shown in the article but it's a lot | larger and it's an animated gif. | | https://drexel.edu/news/~/media/Drexel/Core-Site-Group/News/... | sbierwagen wrote: | If you want to see the actual diagram, rather than the composite | overlaying it with a visible light image of the milky way, here | is figure 4 from the paper: | https://res.cloudinary.com/icecube/images/q_auto/v1671570509... | (From the media gallery here: | https://icecube.wisc.edu/gallery/high-energy-neutrinos-from-... ) | | As you'd expect, the resolution from a 86x60 neutrino detector | array is not great. | causality0 wrote: | Right. That doesn't seem to line up super well with the | galactic disc. Even those diagrams look like they've had an | awful lot of smoothing. | _Microft wrote: | > _" In the Milky Way Galaxy, cosmic rays (high-energy | protons and heavier nuclei) interact with galactic gas and | dust to produce both gamma rays and neutrinos."_, from the | article | | The detected neutrinos were not necessarily produced in the | vicinity of the source of the cosmic rays as I understand it. | Imagine it like a bank of fog lighting up in the night | because a car with headlights is moving towards it. | NoMoreNicksLeft wrote: | I don't think I understand any of this. You have to bury a few | zillion tons of water in a pitch-black salt mine a mile | underneath the surface, and run detectors that see a dim flash of | light when one of these hits a water molecule, right? | | How is that in any way directional? Or is there a way to compile | an image from this without directionality? | _Microft wrote: | The "dim flash of light" is called Cherenkov radiation and | there's directional information encoded in it. Depending on | which (or when a?) particular detector saw that light, the | direction of the incoming particle can be calculated. | | https://en.wikipedia.org/wiki/Cherenkov_radiation | SpectralName wrote: | In addition to the other answers already posted, the neutrino | may hit multiple water molecules along its path, or its decay | products may hit other molecules themselves, so you get many | flashes if you're lucky. | | But another category of detector [1] adds additional signal by | applying a strong, constant electric field vertically across | the entire detection chamber (heavy noble gas, not ice, in this | case). Then whatever charged particles are produced drift up to | the top of the tank, are annihilated there, and you get a flash | that gives you extra good localization in the z direction since | you know how long it took them to get there. | | [1] https://en.m.wikipedia.org/wiki/Time_projection_chamber | Taniwha wrote: | Icecube is at the south pole - the zillions of ton s of water | is just ice | sjackso wrote: | The detector is made of thousands of light sensors arranged in | a a km-scale 3D grid. When a neutrino interaction causes a | flash of light inside this volume, multiple sensors detect the | photons with nanosecond-level time resolution. So a 3D map can | be made of where the light started and how it moved over time. | | For a macroscale analogue, imagine a large 3D grid of | microphones all recording sound. If you fired a cannon from | inside this grid and looked at the waveforms from all the | microphones, you could work out where the cannon was, and also | form a pretty good guess of what direction it was pointed. | 0PingWithJesus wrote: | The only neutrino detector placed in a salt mine was the IMB | detector. That detector was ~10kt of water observed by ~2 | thousand photo-detectors, it was located ~600meters | underground. The only neutrino detector that's a mile | underground was the SNO detector, which was ~1kt of water, | observed by ~10 thousand photo-detectors. The SNO detector is | still running today as the rechristened SNO+ experiment. | | Both the IMB and SNO detectors used electron scattering to | observe neutrinos, a neutrino comes in and bumps into an | electron orbiting an atom, the electron & neutrino both then go | flying off. The electron will usually go off in the same | approximate direction that the neutrino was traveling, | conservation of energy and momentum requires that. The | electron, if energetic enough, emits Cherenkov radiation as it | goes. Cherenkov radiation is just the light equivalent to a | sonic-boom, it is emitted in a cone centered around the | electrons direction of travel. The light from that cone is | detected by the photo-detectors. Crucially, both the | interaction process (electron-scattering) and the detection | process (Cherenkov radiation) will preserve the directionality | from the original neutrino (for the most part). The pattern of | photo-detectors that gets hit by the Cerenkov light can be | analyzed to reconstruct the Cerenkov cone and estimate the | original neutrinos direction. Here's an example of an observed | Cerenkov ring at the Super Kamiokande detector, although this | example is very clear, the Cerenkov rings aren't always so | obvious. https://cerncourier.com/wp- | content/uploads/2016/07/CCthe1_06... | | Also the Super Kamiokande experiment used this sort of analysis | to produce a "neutrino picture of the sun", which is kind of a | predecessor to the OP image. https://www- | sk.icrr.u-tokyo.ac.jp/en/sk/about/research/ | | The IceCube detector is somewhat different. Their photo- | detectors are buried in the Antarctic ice at various depths | from ~1-2km and spread out over a roughly 1-cubic km volume, | which is ~1Gt of water. I'm not exactly sure how many PMTs in | total they have, I reckon its probably around 5-10 thousand. | Since their PMT array is so much less dense than the previously | mentioned experiments, they can only observe very high energy, | very bright, light flashes. So neutrino sources that are low | energy, like the Sun, are invisible to them. But, they can see | sources that are very high energy, and Ice Cube's extraordinary | size lets them observe interactions that are rare/infrequent, | such as those from very far away galaxies. | | High energy neutrinos will almost always interact via "Deep | Inelastic Scattering" (DIS), which is basically the neutrino | hitting the protons & neutrons within an atomic nucleus. Since | DIS is a scattering process, conservation of energy/momentum | requires the scattered particles will preferentially travel in | the same direction that the incoming neutrino was traveling in. | After that Cerenkov radiation is produced from the scattered | protons & neutrons, and that Cerenkov radiation still is | emitted in a cone pointing in the direction of travel. So once | again, the interaction (DIS) and detection (Cerenkov radiation) | preserves directional information. So the pattern of which | photo-detectors observe the light can be used to reconstruct | that direction, and point back to the neutrinos source | (approximately). | wthomp wrote: | As has been pointed out elsewhere, this is the first image of our | galaxy in something other than light (radio, infrared, x rays, | gamma rays are all photons). | __MatrixMan__ wrote: | Odd timing, given that only a few days ago we were talking | about a gravitational wave background | (https://astrobites.org/2023/06/28/drop-the-bass-evidence- | for...) not that we're in a position to render that as an | image, but it's close. | nonameiguess wrote: | Unfortunately, the actual paper seems to be paywalled, but | stories like this often seem to do a poor job of motivating why | research like this is interesting. | | For both this and all of the articles coming out about | gravitational wave detection, these technologies allow us to | sense things that can't be seen with light. Gravitational waves | are produced by binary black hole systems and mergers, which | don't give off any detectable radiation, and neutrinos can be | produced by spin down of neutron stars we don't have any other | easy way of detecting. | | But, these also potentially give us a window into the deep past. | The cosmic microwave background represents the furthest back in | time we can ever see with light, and it happened during the first | formation of neutral hydrogen atoms when the universe first | cooled enough to allow that, and thus light could travel without | being immediately scattered by free electrons, which was 378,000 | years after the Big Bang. Seeing anything before that is | impossible. | | Neutrinos, however, first decoupled from matter 1 second after | the Big Bang. The possibility of being able to detect a cosmic | neutrino background from this event would allow us to detect the | early universe much earlier than we can with light. And if | gravity decoupling from the strong and electroweak forces is ever | detectable in a cosmic gravitational wave background, that would | have happened even earlier, and represents the earliest possible | viewing of the universe by any means whatsoever. | | I'm not a cosmologist and have no idea what usable data would | ever come from being able to see these things, but keep in mind | at least one reason we've had so much difficulty developing a | grand unified theory and theory of everything even after | conquering electroweak, is the inability to produce the enormous | energies required to recouple the forces in a lab. A particle | accelerator that could do it for strong force recoupling to | electroweak would have to be the size of Pluto's orbit. But there | is at least one event in nature where the necessary energy | existed, which is the early universe. We've just never been able | to see it. | _Microft wrote: | The paper is here, for those who directly want to go there | instead: https://www.science.org/doi/10.1126/science.adc9818 ___________________________________________________________________ (page generated 2023-06-29 23:00 UTC)