From Science:
A collaboration of Chinese and Japanese astrophysicists has reported the highest energy photons ever seen: gamma rays with energies up to 450 trillion electron volts (TeV).
The particles of light were traced back to the Crab nebula, the remnant of a stellar explosion observed by Chinese astronomers nearly 1000 years ago, and the powerful pulsar, a dense neutron star, that now sits at the nebula’s heart. “We know the environment of a pulsar is extreme,” says Geraint Lewis, an astrophysicist at the University of Sydney in Australia who was not involved in the research. The question raised by the finding “is just how extreme,” he says. He says the results will help constrain ideas about how the photons are boosted to such extraordinary energies.
More on this over the jump, as well as tonight’s comments, but first, a word from our sponsor:
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A pulsar is a rapidly spinning neutron star, the remnant of a supernova, where the spinning can be detected by the regular periodic radiation coming from it. Astronomers discovered the pulsar at the center of the Crab Nebula. Of course the glowing gas of the nebula, its most obvious visible signature, is due to the surface of the collapsing star violently expelled when the supernova occurred.
The research team wanted to see if it was possible to detect extremely high energy light (gamma rays), and they did so by constructing a detector consisting of 600 scintillation counters arrayed on 66,000 square meters of the Tibetan plateau. What happens when high-energy radiation hits particles in the atmosphere is that a cascade forms as the energy is distributed in many photons and other particles carrying smaller amounts of energy (though still quite formidable). When a particle in a cascade hits a scintillation detector, a flash of visible light is generated and detected. If a cascade is taking place, there will be many such flashes among the detectors in the array in a short period of time. (Cosmic rays can also cause such cascades, but because cosmic rays also produce particles called muons, it’s possible to distinguish between the two. The team had a means for the detection of muons for this purpose.)
Between February 2014 and May 2017, the team detected 24 gamma ray photons ranging between 100 TeV and 450 TeV. (TeV = tera electron volts or one trillion electron volts.) This dwarfs the previous record of 75 TeV. (For comparison, photons of visible light have energies ranging roughly between 2-4 eV.) Because light travels in straight lines (unlike cosmic rays), it was possible to determine that these photons were coming from the Crab Nebula. Theorists had proposed that there was a process by which pulsars could indeed generate light with such massive energy, but before this observation, the idea was considered mere speculation.
Having successfully detected light photons with energies greater than 100 TeV, the researchers have an even bigger number they ant to try: 1000 TeV = 1 PeV (peta electron volt). We’ll seee if they’re up to the challenge.
Top Comments (July 9, 2019):
From Otteray Scribe:
Jake Bodhi left a comment with important information about warming in the Gulf of Mexico in Morning Open Thread. I was unaware of how bad it has gotten, and it is sobering. Also note the replies by Ice Blue and P Carey. In an earlier comment on the same MOT, Jake says he has traded his half-gallon water cooler for a one-gallon cooler. Understandable.
From wasatch:
this comment by Missourilefty is well-written and succint summary of Republican lies about Christopher Steele, and Russians assisting Republicans. From pollwatcher’s recommended post.
From CwV:
HoundDog asked a question about disBarr which touched off a string in which we got to snark cubed. From Kerry Eleveld’s front page post.
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