Ultrahigh-energy photons up to 1.4 PeV from 12 γ-ray Galactic sources (2021)(nature.com)
nature.com
Ultrahigh-energy photons up to 1.4 PeV from 12 γ-ray Galactic sources (2021)
https://www.nature.com/articles/s41586-021-03498-z
42 comments
About 20 years ago, I was on trans-oceanic flight. Coffee was served at some point in the flight, and I am convinced the steam coming off the beverage, along with the higher altitude created a cloud chamber in front of me.
While the coffee cooled, there were very distinct cosmic ray patterns within the steam that I cannot come up with any other explanation for.
While the coffee cooled, there were very distinct cosmic ray patterns within the steam that I cannot come up with any other explanation for.
Thanks for saying this. I've seen the same and wouldn't have thought of this explanation
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> https://youtu.be/xky3f1aSkB8
On a highly unrelated note, looking at the video, the lady looks and sounds kind of familiar. US LHC, nah, too far, not probable. But then - "Filmed in CERN's S'Cool Lab". Bingo (I live in Geneva, Switzerland where we have CERN) - I did some hikes and climbing with her maybe some 7 years ago.
The world is sometimes surprisingly small. And yeah, its amazing how little equipment can get you so far.
On a highly unrelated note, looking at the video, the lady looks and sounds kind of familiar. US LHC, nah, too far, not probable. But then - "Filmed in CERN's S'Cool Lab". Bingo (I live in Geneva, Switzerland where we have CERN) - I did some hikes and climbing with her maybe some 7 years ago.
The world is sometimes surprisingly small. And yeah, its amazing how little equipment can get you so far.
This was always my favorite exhibit at the Exploratorium.
For laymen, can someone who is knowledge put this into persepective ?
1.4 PeV are about 0.224 millijoules or roughly an 8 billionth of a phone charge, so not much really. However, the photons we usually deal with are weaker by an unimaginable amount, but also much more plentiful. For example, a 100 W light bulb emits something in the order of 10^21 photons per second. If you had a light bulb that emitted the same amount of photons with 1.4 PeV each, you'd have a device equivalent to one Tsar bomb (the most powerful bomb ever detonated in the history of mankind) every second.
It's roughly the amount of kinetic energy in a single grain of rice if you gently throw a handful of them. It's not much, but it's not an inconceivably small amount of energy either.
Comparing it to a phone charge is less useful because batteries store a lot of energy (especially when converted to kinetic energy).
Comparing it to a phone charge is less useful because batteries store a lot of energy (especially when converted to kinetic energy).
Yeah. Wolfram Alpha compares it to (a fraction of - something like 20%) the energy of pushing a key on a keyboard.
For one photon to have enough energy to push a rice grain is just crazy.
Makes me wonder which physical process created it. Even the hydrogen fusion photon is not that energetic.
For one photon to have enough energy to push a rice grain is just crazy.
Makes me wonder which physical process created it. Even the hydrogen fusion photon is not that energetic.
I would say that 1.4 PeV is enough energy (by a large margin) to be audible. If that photon interacted with something near you and deposited any respectable fraction of its energy as heat or kinetic energy on a macroscopic scale, you would hear it!
Perhaps it would sound something like the house settling.
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That's a big old phone battery: 8 billion times 0.2mJ is a 120000mAh 3.7V battery.
But yes, it's in that ballpark and it's a loooot of energy to pack into a proton.
But yes, it's in that ballpark and it's a loooot of energy to pack into a proton.
It’s x100 times more powerful than the collider at CERN. 14TeV vs 1.4 PeV. To put it into context, 1 TeV is the energy a mosquito uses to fly. It doesn't sound like much, but for a particle as small as a photon it's a huge amount of energy.
It's maybe worth mentioning that the beams at CERN are made of quite a few particles and there was as much energy in the beam as in a high speed train (and same in the magnets), before the high luminosity upgrade. The beam dumps are massive pieces of graphite and concrete with water cooling.
Also at these energies the wavelength is very small so the energy can be quite concentrated in a small region of space-time.
Also at these energies the wavelength is very small so the energy can be quite concentrated in a small region of space-time.
Question: how come a photon can carry a variable amount of energy? (Layman here, I would have guessed that photons travel at the speed of sound, and are of fixed size and energy, like electrons.)
Photons do indeed all travel at the same speed, but are not all the same size, and what affects their energy level is their wavelength.
Shorter wavelengths have more energy per photon, so e.g. a photon of blue light has about half the wavelength of a photon of red light and twice the energy.
I’m curious if you really meant “speed of sound” in your question? Photons all travel at the speed of light, which is quite a lot faster than the speed of sound. But I’ve seen this several times from different places, and never found out if it’s basically just auto-complete in the speaker’s mind, or a genuine misconception.
Shorter wavelengths have more energy per photon, so e.g. a photon of blue light has about half the wavelength of a photon of red light and twice the energy.
I’m curious if you really meant “speed of sound” in your question? Photons all travel at the speed of light, which is quite a lot faster than the speed of sound. But I’ve seen this several times from different places, and never found out if it’s basically just auto-complete in the speaker’s mind, or a genuine misconception.
I meant speed of light. Yes. That was a typo / brain glitch. Thank you for your explanation, helped a lot.
Photons are massless and hence always travel at the speed of light.
Photons have a wavelength, and that determins their energy; photons of a same wavelength will all have the same energy; the photons discussed in this article have very short wavelength and very high energy (this energy is proportional to their frequency and inversely proprotional to their wavelength).
Regarding electrons; electrons have mass, and they all have the same mass. They have energy associated with this mass, and they also have energy associated with their momentum, thus they don't all have the same energy.
Photons have a wavelength, and that determins their energy; photons of a same wavelength will all have the same energy; the photons discussed in this article have very short wavelength and very high energy (this energy is proportional to their frequency and inversely proprotional to their wavelength).
Regarding electrons; electrons have mass, and they all have the same mass. They have energy associated with this mass, and they also have energy associated with their momentum, thus they don't all have the same energy.
> and like all Bosons are massless and hence always travel at the speed of light
Not every boson is massless and not every boson is travelling at the speed of light (because there are bosons with mass).
Take for example the Higgs boson or the W-bosons.
Not every boson is massless and not every boson is travelling at the speed of light (because there are bosons with mass).
Take for example the Higgs boson or the W-bosons.
ah, thank you; I will correct above
Here's another way to put this into perspective:
Photons carry momentum, although it's too small to be perceptible under ordinary circumstances. If a typical photon of sunlight hits an oxygen molecule in the Earth's atmosphere, and deposits all its momentum, it's enough to give that molecule a "kick" of a few centimeters per second.
In contrast, a single one of these cosmic ray photons carries enough momentum (if it could somehow be delivered in the right way) to accelerate an entire E. coli bacterium, weighing as much as billions of oxygen molecules, to supersonic speeds.
Photons carry momentum, although it's too small to be perceptible under ordinary circumstances. If a typical photon of sunlight hits an oxygen molecule in the Earth's atmosphere, and deposits all its momentum, it's enough to give that molecule a "kick" of a few centimeters per second.
In contrast, a single one of these cosmic ray photons carries enough momentum (if it could somehow be delivered in the right way) to accelerate an entire E. coli bacterium, weighing as much as billions of oxygen molecules, to supersonic speeds.
Imagining a cartoon image of it flying through the air yelling "Wheeeeee!" :)
Its 100 times as much energy per photon than we as humans are able to accelerate particles in the cern large hadron collider with everything we have. It is a stupendous amount of energy per photon.
https://en.wikipedia.org/wiki/Oh-My-God_particle might help.
There is another, imo even better, page on this particle:
https://www.fourmilab.ch/documents/OhMyGodParticle/
https://www.fourmilab.ch/documents/OhMyGodParticle/
Wonder if anyones re-looked at that origin path of the OMG particle in more recent times.
The state of the art observatory for ultra high energy cosmic rays is the Pierre Auger Observatory in Argentina (auger.org). Unfortunately the funds for building a 7x larger northern observatory in Colorado were scraped but the NSF during the crisis in 2008. :(
The PAO published an article on the highest energy arrival directions in 2007 (https://arxiv.org/abs/0712.2843) and I was very sad that I wasn't on the author list (yet) at the time since I hadn't been around for a full year. The discovery was a correlation in arrival directions with the known location of supermassive black holes in the center of other galaxies ("active galactic nuclei"). I was less sad when it appeared to have been a statistical fluke a couple of years later (about 3 sigma worth, enough for a discovery claim in astronomy but not in particle physics - PAO is a mix of both disciplines and the arguments were always thrilling).
We then went back to data collection and analysis and became much more cautious about publication of correlation analysis. (I moved on in 2010.) More recently (2018) it looks like there's a higher significance correlation study: https://arxiv.org/abs/1801.06160. An outstanding breakthrough, yet I think in principle this surprises nobody in the field. They also published a paper purely about the anisotropic arrival directions (no correlation analysis with known objects) that showed that far more of the highest energy events arrived from the side facing away from the milky way. This shows (again to no surprise of anybody in the field, but you need to prove it anyway) that these particles are of extragalactic origin. A mechanism that puts this much energy into a single particle might not be conducive to life nearby (ie. in the same galaxy).
With that background back to your topic of inquiry: Regarding origin paths of such high energy particles.
~All ultra high energy cosmic rays are believed to be charged particles. That means their path is changed by galactic and intergalactic magnetic fields. (Mostly the latter, they are weaker but the distances are so very much longer.) That means the higher the particle's energy, the less it's path will be bent by the magnetic fields. At lower energies, they are basically arriving from random directions (isotropically) because their paths are bent into curves. We don't have a great way to get super accurate models of these magnetic fields (I lack the detailed background to comment on the theory here). Still, at these energies and with the upper limits that we believe about the strength of the fields, and with the measurement accuracy of the more modern PAO detectors (angular resolution better than 1 degree) we get something on the order of a few degrees or so (didn't have a chance to reread entire paper, this is from memory) in terms of uncertainty on the arrival direction.
The upshot of that is that a single event isn't really useful on its own. There's also significant uncertainty in the energy measurement, so again, a single event like the flys eye event doesn't make for finding an origin. But the larger dataset does, if you match it against potential sources. (In case you're wondering: yes, one has to be careful with bias in those analyses.)
The PAO published an article on the highest energy arrival directions in 2007 (https://arxiv.org/abs/0712.2843) and I was very sad that I wasn't on the author list (yet) at the time since I hadn't been around for a full year. The discovery was a correlation in arrival directions with the known location of supermassive black holes in the center of other galaxies ("active galactic nuclei"). I was less sad when it appeared to have been a statistical fluke a couple of years later (about 3 sigma worth, enough for a discovery claim in astronomy but not in particle physics - PAO is a mix of both disciplines and the arguments were always thrilling).
We then went back to data collection and analysis and became much more cautious about publication of correlation analysis. (I moved on in 2010.) More recently (2018) it looks like there's a higher significance correlation study: https://arxiv.org/abs/1801.06160. An outstanding breakthrough, yet I think in principle this surprises nobody in the field. They also published a paper purely about the anisotropic arrival directions (no correlation analysis with known objects) that showed that far more of the highest energy events arrived from the side facing away from the milky way. This shows (again to no surprise of anybody in the field, but you need to prove it anyway) that these particles are of extragalactic origin. A mechanism that puts this much energy into a single particle might not be conducive to life nearby (ie. in the same galaxy).
With that background back to your topic of inquiry: Regarding origin paths of such high energy particles.
~All ultra high energy cosmic rays are believed to be charged particles. That means their path is changed by galactic and intergalactic magnetic fields. (Mostly the latter, they are weaker but the distances are so very much longer.) That means the higher the particle's energy, the less it's path will be bent by the magnetic fields. At lower energies, they are basically arriving from random directions (isotropically) because their paths are bent into curves. We don't have a great way to get super accurate models of these magnetic fields (I lack the detailed background to comment on the theory here). Still, at these energies and with the upper limits that we believe about the strength of the fields, and with the measurement accuracy of the more modern PAO detectors (angular resolution better than 1 degree) we get something on the order of a few degrees or so (didn't have a chance to reread entire paper, this is from memory) in terms of uncertainty on the arrival direction.
The upshot of that is that a single event isn't really useful on its own. There's also significant uncertainty in the energy measurement, so again, a single event like the flys eye event doesn't make for finding an origin. But the larger dataset does, if you match it against potential sources. (In case you're wondering: yes, one has to be careful with bias in those analyses.)
At 320 EeV, the OMG particle is over 5 orders of magnitude more than 1.4 PeV. It's a completely nuts amount if energy to have in a single particle: about the same as a decently moving baseball. From the particle's frame, it takes only a day to go a billion light years.
> about the same as a decently moving baseball
I heard this, but it's hard to believe it's real (or, obviously, I'm misunderstanding it). What would happen if one of these hit a person in space? Would it be the same sort of feeling as getting hit by a baseball?
Earlier I wondered how this much energy didn't totally wreck the detector, but someone else posted this link https://www.fourmilab.ch/documents/OhMyGodParticle/, which says "The Fly's Eye consists of an array of telescopes which stare into the night sky and record the blue flashes which result when very high energy cosmic rays slam into the atmosphere". So the protons don't actually hit the detector. That makes more sense.
I heard this, but it's hard to believe it's real (or, obviously, I'm misunderstanding it). What would happen if one of these hit a person in space? Would it be the same sort of feeling as getting hit by a baseball?
Earlier I wondered how this much energy didn't totally wreck the detector, but someone else posted this link https://www.fourmilab.ch/documents/OhMyGodParticle/, which says "The Fly's Eye consists of an array of telescopes which stare into the night sky and record the blue flashes which result when very high energy cosmic rays slam into the atmosphere". So the protons don't actually hit the detector. That makes more sense.
It doesn't interact like a baseball, it just has the energy of one.
If it does hit an atom, it produces a shower of other particles, most of which will have similarly huge energies and will probably go right through the rest of the detector and start their own showers in other matter. So you'll get a detector with a few atomic dislocations, and the rest of the energy would be distributed amongst a huge number of other interactions.
It's actually similar to x-ray "hardening", where soft x-rays are filtered out by a metal shield, leaving only harder radiation. This is carefully calibrated to allow the radiation to penetrate to a certain depth, leaving shallower tissue unharmed.
In a way, it could be better to be hit by an OMG particle than a less energetic particle, as the amount of energy that gets dumped into you is smaller: the vast, vast majority of it would be shotgunned deep into the ground under you, and only a very few molecules in you are actually affected.
If it does hit an atom, it produces a shower of other particles, most of which will have similarly huge energies and will probably go right through the rest of the detector and start their own showers in other matter. So you'll get a detector with a few atomic dislocations, and the rest of the energy would be distributed amongst a huge number of other interactions.
It's actually similar to x-ray "hardening", where soft x-rays are filtered out by a metal shield, leaving only harder radiation. This is carefully calibrated to allow the radiation to penetrate to a certain depth, leaving shallower tissue unharmed.
In a way, it could be better to be hit by an OMG particle than a less energetic particle, as the amount of energy that gets dumped into you is smaller: the vast, vast majority of it would be shotgunned deep into the ground under you, and only a very few molecules in you are actually affected.
Correct me if I’m wrong but at a photon’s scale a human is mostly empty space.
Eh, kind of. It depends on the photon. A human is not transparent to visible light: if they were, we'd all be see-through. But we are substantially transparent to gamma rays. The same goes for baryons like protons: proton beam therapy can reach deep into humans, but alpha radiation (which is 2 protons and 2 neutrons, so not much "bigger") will be stopped by the first layer of skin.
From the an OMG particle's perspective, at that speed, due to Lorentz contraction factor of 300 billion, a human is only a few picometres across.
From the an OMG particle's perspective, at that speed, due to Lorentz contraction factor of 300 billion, a human is only a few picometres across.
Can the interaction also be approximated using the wavelength? E=hc/λ -> λ=hc/E -> λ=1.239/(1.4e15)=8.9e-16 μm
Vanishingly small, about 900 yoctometers, or seven orders of magnitude smaller than a proton. No wonder we appear like empty space for the first few cascading reactions.
Now, could dark matter just be photons with absurdly high energy?
Vanishingly small, about 900 yoctometers, or seven orders of magnitude smaller than a proton. No wonder we appear like empty space for the first few cascading reactions.
Now, could dark matter just be photons with absurdly high energy?
No, because dark matter concentrates around mass, which requires it to be able to be at rest to normal matter.
Aha! I see.
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https://www.snolab.ca/outreach/resources-for-students-educat...
"Build a particle detector":
https://www.snolab.ca/wp-content/uploads/2021/11/Build-a-par...
https://youtu.be/xky3f1aSkB8
"Cosmic Rays and the Cloud Chamber":
https://crater.unh.edu/pdfs/CosmicRayBook.pdf