Supernovae are some of the most energetic events in the Universe. And a subset of those involves gamma-ray bursts, where a lot of the energy released comes from extremely high-energy photons. We think we know why that happens in general terms—the black hole left behind after the explosion expels jets of material at nearly the speed of light. But the details of how and where these jets produce photons are not at all close to being fully worked out.
Unfortunately, these events happen very quickly and very far away, so it's not easy to get detailed observations of them. However, a recent gamma-ray burst that's been called the BOAT (brightest of all time) may be providing us with new information on the events within a few days of a supernova's explosion.
[...] The "telescope" mentioned is the Large High Altitude Air Shower Observatory (LHAASO). Based nearly three miles (4,400 meters) above sea level, the observatory is a complex of instruments that aren't a telescope in the traditional sense. Instead, they're meant to capture air showers—the complex cascade of debris and photons that are produced when high-energy particles from outer space slam into the atmosphere.
(Score: 3, Interesting) by quietus on Sunday June 11, @01:57PM (2 children)
The system seems (part of the website is still under construction) based on a water Cherenkov detector array, built to detect Cherenkov radiation [wikipedia.org].
A particle passing through a material at a velocity greater than that at which light can travel through the material emits light. This is similar to the production of a sonic boom when an airplane is traveling through the air faster than sound waves can move through the air (according to wikipedia). Call me stupid, but this is new to me -- I've always thought that the speed of light/photons was the limiting factor everywhere, not that it was dependent on the medium. (But ofcourse, muon particles travel straight through earth, while photons don't.)
This thing is originally intended to study photons with an ultra-high energy of more than 1 petaelectronvolt, produced in locations called PeVaTrons [nature.com] -- cosmic ray factories which accelerate particles to PeV energies.
Question by the completely innocent and slightly foolish: could these acceleration centres act like [non-gravitational] lenses, distorting our observation of the universe? Would they have an impact on communication between earth and a far-into-the-future space ship?
Feel free to slap me (gently) around the ears, here.
(Score: 1, Informative) by Anonymous Coward on Sunday June 11, @06:45PM (1 child)
The speed of light in a material is the speed of light in a vacuum (the one you're thinking about) divided by the index of refraction of the medium through which it is traveling, so roughly speaking the speed of light in glass is about 1/1.3 ~ 77% of the speed of light in vacuum. When a charged particle passes through matter, it excites the medium as usual, but if it is traveling faster than light in that medium (in the case of glass, say it is traveling at 0.8C), it is exactly like the sonic boom where the light forms a coherent wavefront that creates a cone of disturbance, where in this case the photons being emitted are all bunched up in a wavefront that arrives like a pulse of light. To tease even more info out of this, the cone travels in the direction of the particle, and if you have an imaging detector that intercepts that cone, it will see a ring of light that will look circular if coming perpendicular to the detector, or like an ellipse if coming in at an angle. The angle of the cone, and hence the size of the detected circle/ellipse, is dependent upon the speed of the particle too, so if you know your index of refraction very well, you can not only detect these particles, but also get their directions and speeds if you have the right detector.
Cherenkov detectors act as nice threshold detectors because they won't generate any radiation until the particle exceeds some minimum speed (momentum) threshold. So the trick on these detectors is to tweak the index of refraction to get it where you want to put your momentum cutoff. This is often done using gases because you can tweak the index of refraction by tweaking the pressure of the gas.
The particles you're thinking about that travel through the earth are neutrinos, not muons. By the way, the huge underground water tank neutron detectors are operated as Cherenkov detectors for neutrinos that travel up through the earth and interact in the water tank, kicking off electrons that create Cherenkov radiation that is detected by thousands of photomultiplier tubes. From the signal characteristics they can tell if the detected radiation came up through the earth or down from above.
I'm not sure if I understand your last question. I don't see how they would act as non-gravitational lenses, but I'm probably not understanding what you're asking.
(Score: 2) by quietus on Tuesday June 13, @01:49PM
Thanks for the clear and lucid explanation.
As for my last question, that was really about the nature of those PeVatrons. I might have misread here: the quoted nature article mentions factories of ultra-high cosmic rays, while I was thinking about acceleration centres i.e. something like a fast-rotating pulsar taking photons and doing the equivalent of a gravitational slingshot flyby. (I am most likely, and very naively, muddling different concepts together here.) That would not act as a lens, but it would distort the true origin of those photons hence, at a large enough scale, would make things appear at a different location than in reality.
(I'd appreciate if you wouldn't die laughing after reading the above -- such is the confusion of a non-physicist in times of high temperature and lack of cold beers, close-by.)
(Score: 5, Insightful) by bzipitidoo on Sunday June 11, @04:18PM
Uh, no, I call that fortunate not to be so near that it harms us.
Supernovae are energetic, but I am still stunned by how much energy is released when 2 black holes merge. In seconds, merging black holes release more energy than the sun has produced in its entire 4.6 billion years of existence.