I’m only a few weeks late on this, I think, on this, and figure somebody with good cites will come along.
Via a miles-deep sensor apparatus under the ice–which sounds fascinating to begin with–they found traces of real live neutrinos. I understand, sort of, that these are extremely hard to spot. What’s the big news here–
The experiment is called IceCube Neutrino Observatory and it’s in Antarctica not the Arctic.
In July 2018 they reported the detection of a high energy neutrino. They traced the path back to a blazar 3.8 billion lightyears away and associated it with cosmis rays. Since cosmic rays are charged particles their paths may bend making a traceback difficult. Neutrinos however plot straight through everything.
Paper #1 Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A
paper #2 Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert
Neutrinos are detected all the time. We can even generate them in a particle accelerator and detect them from hundreds of miles away.
High-energy neutrinos, with energy tens of TeV (that’s higher energy than the LHC can produce) are rare, but they are still regularly observed.
What’s new is, when IceCube detected this high-energy neutrino, they were able to calculate the direction it came from, and relay it to other observatories around the world very quickly, to see if the source of the neutrino could be detected in some other way. And they did detect it - a blazar in the same part of the sky brightened around the same time. Which is not conclusive, but a pretty good indication that this blazar was the source of the high-energy neutrino.
The really exciting part is, this may indicate where ultra-high energy cosmic rays come from. Because that’s been a long-standing mystery in astrophysics. Although there are reasons to be cautious, as explained here.
When they trace a path, how do they know that the path hasn’t been affected by gravity somewhere along the way?
They account for curvature by using the light path, which accounts for this effect. The curve of space time effects light too.
Sure, but how do they know the neutrino didn’t start from some other area of the universe, and by passing massive, unseen black holes or whatever, had it’s path altered due to gravity and now just looks like it came from the blazar?
Consider the following:
Blazar shoots off light, neutrinos and charged particles (cosmic rays)
Charged particle follows gravitational fields, get deflected by magnetic field and hits your eye from an angle
Light follows gravitation fields (might get absorbed by dust) and hits your eye (if it makes it)
Neutrino follows gravitational fields, didn’t even notice the dust was there, and hits your eye.
Gravity is a very weak force, so we don’t see much gravitational distortion in astronomical observations. Even the prominent counter-examples (gravitaitonal lensing) deflect light by only a tiny fraction of a degree.
This is just one observation. Nobody is saying it’s a conclusive proof of anything. You don’t even have to postulate a mysterious invisible black hole to poke holes at this explanation - it’s possible that the neutrino was generated by some other object in the same part of the sky, and it’s just pure coincidence that a blazar happened to be near it.
But if this explanation is correct, then eventually we’ll see more neutrinos that appear to come from other blazars that brightened at the same time. Then we’ll be more confident about it.
Plus a Blazar is really the only known object that could possibly create these high energy particles, which means when we look where we think it came from it seriously reduces the amount of possible sources.
For physical particles, like the Oh-My-God particles that are protons from these blazars are traveling so close to the speed of light that it would take a photon over 200 thousand years to gain 1 cm on that proton traveling the same path.
Absent any breakthroughs in physics, we know of nothing that can impart this much energy in our universe outside of a blazar.
That was my next question. Thanks for all the answers!
As for how exciting this is: So far, it’s just adding confirmation to things that we already suspected were true. That’s nice, but it’s hardly Earth-shattering. Down the line, it may well lead to new ideas, but that’s always difficult to predict.
I just want to say, and gloat, how I once, lo those twenty years ago, designed those aluminum extrusions used in neutrino detectors.
Okay, some guy from Switzerland did the actual design, but I made them extrudable. Brilliant, but Hans didn’t know shit about extrusions.
The first astronomical neutrino detector was setup in 1970 and detected neutrinos from the Sun. 8 light-minutes away.
The first detection of neutrinos from a known source outside our solar neighborhood was in 1987 from the supernova SN 1987A, 168,000 light-years away in the Large Magellanic Cloud.
The recent event is the first detection from well outside our galactic cluster at 3.8 billion light-years.
Note that if someone says “Hey, there’s something going on now at such-and-such location, somebody take a look.” and someone looks and sees an intense short term even occurring there, the chances of this being an coincidence goes way down. Esp. at the energy levels we’re talking about. Two such rare events in the same direction at the same time? C’mon.
How convincing that is depends on just how precisely you can measure “the same direction”. Neutrino detectors aren’t generally as precise as electromagnetic telescopes (though probably better than gravitational-wave detectors).
As to “simple” geometric location Out There–which I know is a laughably complex topic in which even to pose this question–can that precision as to “direction” be quantified in arc-seconds, or something like that, given the type of stellar object being tracked?
Hubble can measure to 0.05 arcseconds and actual resolution near 0.1 arcseconds. Gaia can measure to 7 - 20 microarcseconds (µas) depending on a few factors like brightness.
To put this in context, 7 µas is about the width of a human hair in Richmond, VA as viewed from Chicago.
Another example that doesn’t depend on a knowledge of those locations.
1 microarcsecond is about the size of a printed period on the surface of the moon as viewed from the earth. When combining Hubble and Gaia data this is about the resolution we have today.
But if we’re comparing locations from multiple instruments, then what matters is the resolution of the lowest-resolution instrument (actually probably something like the Pythagorean sum of both of the resolutions, but when they differ by orders of magnitude, that amounts to about the same thing). And the resolution of IceCube is only on the order of a degree.
