Cosmic Rays, Man
July 12, 2018 4:44 PM   Subscribe

When a subatomic particle from space streaked through Antarctica last September, astrophysicists raced to find the source. Multiple teams of researchers from around the world describe the neutrino's source in at least seven papers released on 12 July.
posted by condesita (21 comments total) 21 users marked this as a favorite
 
From TFA: "Within seconds, a computer cluster ... had reconstructed the precise path of the particle and recognized that the muon had come from a highly energetic neutrino"

I, on the other hand, struggle to find my car in a parking lot.
posted by GuyZero at 4:50 PM on July 12, 2018 [14 favorites]


This is super cool. I liked Vox's article on this; enough science to be interesting, but still readable.

One single neutrino! That's amazing. One thing I don't understand is that apparently several neutrinos a year light up the detector; why is this the one that is so important?

Between this result and LIGO it's a good decade for observational astronomy.
posted by Nelson at 5:02 PM on July 12, 2018


For anyone wondering why neutrinos interact so rarely with matter it's because they only interact with the weak force and gravity. For why this means neutrinos are like cosmic ghosts, this brilliant video from Fermilab explains why the weak force is "weak" and hence why neutrinos interact so rarely.
posted by Definitely Not Sean Spicer at 5:02 PM on July 12, 2018 [6 favorites]


One thing I don't understand is that apparently several neutrinos a year light up the detector; why is this the one that is so important?

Because normally they can't assign a source to these neutrinos. There's only so many eligible sources cataloged and because neutrinos rarely interact with matter they can come from virtually anywhere in the universe. They got one where they could backtrack the source, pin point it, and correlate it with spikes in other radiation from that source.
posted by Definitely Not Sean Spicer at 5:07 PM on July 12, 2018 [4 favorites]


Is he still around, kalessin?

Because I think cosmic rays are way more important all up and down in biology than people realize, and if he has unpublished work that was too wild for his time, he could be an unrecognized pioneer.

I think this discovery is as exciting as the detection of gravitational waves, really.
posted by jamjam at 5:11 PM on July 12, 2018


I'm so sorry to hear that, kalessin!

I bet he was wonderful along multiple axes.
posted by jamjam at 6:01 PM on July 12, 2018 [1 favorite]


... correlate it with spikes in other radiation from that source.

Is there a group delay (dispersion factor) associated with the different particle energies?
posted by ZenMasterThis at 6:03 PM on July 12, 2018


IceCube — an array of more than 5,000 sensors buried in a cubic kilometre’s worth of ice: splendid.
posted by doctornemo at 6:19 PM on July 12, 2018


It is crazy that physicists are able to reconstruct the precise path of something just from the subatomic debris of the collision that destroyed(?) it, when they don't know which direction it came from or how fast it was moving.
posted by straight at 7:23 PM on July 12, 2018 [1 favorite]


Conservation of momentum.
posted by ryanrs at 7:39 PM on July 12, 2018 [1 favorite]


I'm so delighted to learn about the existence of a cosmic phenomenon known as a blazar.
posted by vverse23 at 10:29 PM on July 12, 2018


I'm so delighted to learn about the existence of a cosmic phenomenon known as a blazar.

The Space.com illustration ("An artist's illustration of a blazar...") makes it look like we have discovered God and had Doré illustrate it.
posted by pracowity at 2:03 AM on July 13, 2018 [4 favorites]


ZenMasterThis: technically yes as neutrinos have mass, but the masses are so tiny that even low energy ones won't have speeds measurably different from c.
posted by edd at 2:32 AM on July 13, 2018 [2 favorites]


Adorably cute Japanese explanation in English

(h/t: a physicist friend of mine)
posted by Definitely Not Sean Spicer at 4:46 AM on July 13, 2018 [5 favorites]


One thing I don't understand is that apparently several neutrinos a year light up the detector; why is this the one that is so important?

Because it had a spectacularly high energy, and scientists want to figure out where such high energy cosmic rays come from. This is the main purpose for IceCube. From the Vox article:
“How does nature do this?” Francis Halzen, a University of Wisconsin particle physicist and a lead collaborator on the new discovery, asks. “This has been for decades listed as one of the big open questions in astronomy and physics.”

The problem with looking for the sources of these very high energy cosmic rays is that they don’t always travel in a straight line. And that means they can’t trace it back to its source. In fact, we have the Northern and Southern Lights near the poles because the Earth’s magnetic field redirects much of the cosmic rays to these regions.

This is where the South Pole observatory comes in.

...

Neutrinos are different from the other components of cosmic rays in one hugely important way: They don’t interact with other forms of matter much at all. They don’t have any electrical charge so Earth’s magnetism doesn’t deflect them. And they travel through the universe in a relatively straight line, and we can trace them back to a source.

...

The particular neutrino — and it was just one — that led to the new discovery hit the ice cube in September 2017 with an energy of 290 terra electron-volts. Again, that’s 40 times as energetic as the particles in the LHC.
posted by mubba at 8:04 AM on July 13, 2018 [2 favorites]


Isn't the LHC 13 TeV? Either way, the accelerators I work with are 250MeV, so I'm kind of boggling at the idea of something a million times more energetic.
posted by rhamphorhynchus at 10:31 AM on July 13, 2018 [1 favorite]


The speed of neutrinos is so close to the speed of light, that neutrinos from supernovas in other galaxies arrive hours before visible light. This discrepancy is explained by the fact that stars are opaque to visible light but not neutrinos, and it takes hours for the shock wave from the collapsing core to reach the surface.
posted by GenderNullPointerException at 11:35 AM on July 13, 2018 [2 favorites]


rhamphorhynchus, the 13 TeV at the LHC is the collision energy measured in the center of mass reference frame. Each beam of protons is ~6.5 TeV, so I guess they're approximating the "40 times" there.

This is the main purpose for IceCube.
IceCube is studying many questions in physics, particularly about neutrinos, but they certainly have a unique window to parts of astrophysics other detectors can't begin to touch!
posted by spelunkingplato at 4:16 PM on July 13, 2018 [2 favorites]


Conservation of momentum.

Well sure, that works fine on paper with imaginary billiard balls, but that scientists can actually do it with subatomic particles moving at significant fractions of the speed of light is amazing.
posted by straight at 12:45 AM on July 14, 2018


Thanks spelunkingplato, that makes sense.
posted by rhamphorhynchus at 5:35 AM on July 14, 2018


This puts us one small step further towards eventually being able to harness the Power Cosmic!
posted by homunculus at 7:06 AM on July 14, 2018


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