Story here:
I don’t know enough to comment, but it sounds significant?
I don’t know enough to say anything substantive either, but as a personal thing, I don’t get too excited about this sort of thing. I mean, it’s the type of particle that would be generated by a high-energy source, and they can’t find such a source – yet. Would it be such a surprise if a cosmic ray could have traveled from another galaxy? And that to do so would mean it would have to have been “high energy?” It doesn’t seem groundbreaking on the whole. Come back to me if it proves to contain a signal with instructions on how to travel through a wormhole. (Like I said, this is my personal reaction, maybe if I were less ignorant I would be more excited.)
By the way, I love how the article started by referring to “Space scientists.” Are we to assume that business people would not understand, or would be turned off by, terms such as “astrophysicists?” Or do they mean something else by “Space scientists?”
Badass name, though.
We can see thousands of other galaxies.
The light they emit is a “cosmic ray”.
Unless this one is artificial, here’s nothing new.
Seems like a click-trap…
Light is not a cosmic ray, despite the fact that light is a ray and it’s in the cosmos. Cosmic rays are subatomic particles that are accelerated to high velocities. There’s nothing that will physically prevent cosmic rays from coming from other galaxies. It’s likely many of them do although we usually can’t say which ones.
Lower energy cosmic rays will have their paths bent by magnetic fields, so we can’t tell where they’re coming from if from outside the Solar System. But the higher the energy it has, the less its path is bent by magnetic fields, so we can sometimes tell that a specific ray came from a certain high energy source. In this case, the energy is very high, so it took a very straight path. But there’s no high energy source in that direction within our galaxy, so it must have been a source in another galaxy.
Not clickbait at all.
Scientists from space? They’re here!
From the Business Insider article:
Unlike low-energy cosmic rays, whose origins are traceable, ultra-high-energy particles such as this appear to come from seemingly empty spaces. The Amaterasu particle is believed to originate from the Local Void, an empty region of space bordering the Milky Way galaxy.
The article (like most in BI) isn’t very detailed but in essence the kinetic energy of the detected proton particle was about 2.44x1020 eV, which is almost half an order of magnitude greater than the Greisen–Zatsepin–Kuzmin (GZK) limit which is the theoretical cutoff on the kinetic energy of a proton travelling through the cosmic microwave background (CMB) of the intergalactic medium. There is no known astrophysical phenomenon that would generate protons of this energy, and while this detection isn’t unique it is the second most energetic that we have detected to date, from a direction mostly void of galaxies. Note that because this detector (and most complex cosmic ray observatories) is on the Earth’s surface, and so can only directly detect the small fraction of high energy cosmic rays that get through the atmosphere without colliding with a molecule of air. There are certainly many more events that are not detected because they interact and produce spallation showers of exotic high energy particles which produces most of the “cosmic radiation” we experience on Earth.
Why is this significant? We don’t know the source of these particles or how they manage to apparently travel across intergalactic distances beyond the GZK horizon. This might mean that the source is actually within our galaxy (unlikely), or our understanding of high energy interactions of the CMB is flawed (very unlikely), or something is fundamentally broken in either the theory of special relativity, or particle physics, or both. Fundamentally, it is a big mystery. From a practical standpoint, these extreme high energy cosmic rays present one of the major human health hazards for interplanetary space travel (and even orbital habitation), and unlike the lower energy solar energetic particles it is one we can’t shield from except by enclosing a habitat in a large layer of mass on all sides.
Stranger
If this or the Oh My God particle hit you, would you feel it?
This one was a spallation shower. That’s the only way they can determine direction:
To catch the rarest, highest-energy particles, scientists build giant arrays of detectors. The Telescope Array monitors an area of 700 square kilometers using more than 500 detectors made of plastic scintillator, material that emits light when hit by a charged particle. Additional detectors measure ultraviolet light produced in the sky by the shower of particles (although those detectors weren’t operating during the newly reported particle’s arrival). Based on the times that individual scintillator detectors were hit by the cascade of particles, scientists can determine the direction of the incoming cosmic ray and use that information to trace it back to its origins.
It is a good thing I’m not naming particles, because this second one would be Look At Her Butt.
We detect them because they collide with air molecules.
But yeah, ultra-high-energy cosmic rays are generally assumed to all be extragalactic in origin, because we don’t think there’s anything in our Galaxy that can produce them (but there are things in other galaxies which just might be able to). So the fact that this one specifically is thought to be extragalactic is no big deal. Nor is it unprecedented: The Oh-My-God particle had even more energy.
All that said, detections of cosmic rays this energetic are very rare, and so having another one added to the data set is very good news for scientists studying them.
I like high energy particles and I cannot lie!
No, it would punch right through you, neither imparting measurable net momentum or perceptible heating. However, if it interacted with a nucleus, it would produce a big array of muons and mesons, as well as knocking neutrons and protons out of interacting atoms at very high energy (and potentially relativistic speeds for HZE ions), which could to substantial genetic and cellular damage.
I should clarify that most cosmic ray interactions occur at very high altitude and the exotic particles decay before reaching the Earth’s surface because of their short lifetimes and they aren’t moving at relativistic speeds; early observations of cosmic ray interactions were done with high altitude weather balloons or instruments in crewed hot air balloons for this purpose, and they were also the first experiments to capture the tracks of high energy heavy ion interactions before particle accelerators were powerful enough to generate such particles. The extremely high energy cosmic rays (which are actually particles) can produce spallations moving fast enough that they survive to ground, and while they are rare, they aren’t once in a generation rare; the Pierre Auger Observatory in Argentina, for instance, has detected thousands of ultra-high energy cosmic rays (UHECRs) of (presumably) extragalactic origin over its more than two decades of operation; the Amaterasu particle is just the second most powerful yet detected.
Stranger
On the other hand, just looking at the numbers, 2.44 x 1020 eV is equal to 39 joules. That’s equivalent to the kinetic energy of a regulation 5 oz baseball traveling at 52 miles per hour. If it did interact with you, I think you’d feel it.
The spallations don’t even need to reach the ground. Most of the detectors work by seeing the line of the spallation particles crossing the sky. Well, I guess technically you could say that the photons themselves are spallation particles, and those do reach the ground, but that’s not generally what people mean by “spallation particles”.
And yes, particles energetic enough to be called “ultra-high-energy” aren’t all that rare, but ones as energetic as this particular one, which is more energetic than most UHECRs, are.
What are the categories of things that might produce such rays? Why do we think our galaxies lacks them, but other galaxies do?
Active supermassive black holes. Most or all galaxies have a supermassive black hole at the core, but not all of them are active, and not all of them are the same size. Ours is only about 2.6 million times the mass of the Sun, while some are believed to be as much as 10 billion solar masses. M87, whose central black hole is estimated to be somewhere between 3 and 7 billion solar masses, is considered a likely culprit.
Acrtually, about 4.3 million solar masses. But it’s a shrimp for galaxies the size of the Milky Way. Most are hundreds of millions of solar masses or more.
…Huh. And now I’m wondering how I made that mistake. The current mass figure was derived, with very high confidence, while I was still active in the field, and the previous best estimate wasn’t much different. Where did my brain get the 2.6 million number from?