Saturday, December 03, 2022

Pulsars may power cosmic rays with the highest known energies in the universe

The wind and chaotic remnants around recently exploded stars could launch some of the fastest particles in the universe.

Highly magnetic neutron stars known as pulsars whip up a faster and stronger magnetic wind. When charged particles, especially electrons, are trapped in those turbulent conditions, they can be boosted to extreme energies, astrophysicists reported on April 28. astrophysical journal letters, What’s more, those zippy electrons can proceed to accelerate some ambient light to similarly peak energies, possibly creating the very high-energy gamma-ray photons that led astronomers to recognize these particle launchers in the first place.

“This is a first step in exploring the connection between pulsars and ultrahigh-energy emissions,” says astrophysicist Kay Fang of the University of Wisconsin, Madison, who was not involved in this new work.

Last year, researchers at the Large High Altitude Air Shower Observatory, or LHAASO, in China announced the discovery of the highest-energy gamma rays ever detected, up to 1.4 quadrillion electron volts.SN: 2/2/21) it is about 100 times as energetic as the highest energy achieved with the Large Hadron Collider near Geneva, the world’s leading particle accelerator. Identifying the cause of these and other extremely high-energy gamma rays could, literally, point to the locations of cosmic rays—the zippy protons, heavy atomic nuclei and electrons that bombard Earth from places beyond our solar system. Huh.

Some gamma rays are believed to originate in the same environment as cosmic rays. One way to produce them is that cosmic rays can, shortly after launch, slam into relatively low-energy ambient photons, elevating them to high-energy gamma rays. But electrically charged cosmic rays are affected by galactic magnetic fields, meaning they do not travel in a straight line, thus complicating efforts to trace the zippy particles back to their source. Gamma rays, however, are impervious to magnetic fields, so astrophysicists can trace their unbroken paths back to their origins—and trace where cosmic rays are formed.

To that end, the LHAASO team detected hundreds of gamma-ray photons, which it detected at 12 locations in the sky. While the team identified one location as the Crab Nebula, the remnant of a supernova about 6,500 light-years from Earth, the researchers suggested that the rest may be other sites of stellar explosions or even young giant star clusters. can be associated with.SN: 6/24/19,

In the new study, astrophysicist Emma d’Ona Wilhelmy and her colleagues zeroed in on one of those possible points of origin: pulsar wind nebulas, clouds of turbulence and charged particles surrounding a pulsar. The researchers weren’t sure whether such places could create such high-energy particles and light, so they set out to show through calculations that pulsar wind nebulae were not sources of extreme gamma rays. “But to our surprise, we saw in very extreme conditions, you can interpret all the sources [that LHAASO saw]says d’Ona Wilhelmi of the German Electron Synchrotron in Hamburg.

The young pulsars at the center of these nebulae—no more than 200,000 years old—can provide all that oomph due to their ultrastrong magnetic fields, which create a turbulent magnetic bubble called the magnetosphere.

Any charged particle moving in a strong magnetic field accelerates, says d’Ona Wilhelmi. In this way the Large Hadron Collider accelerates the particles to extremely high energies (SN: 4/22/22) a pulsar-powered accelerator, however, could accelerate the particles to even higher energies, the team calculates. This is because electrons escape from the pulsar’s magnetosphere and meet material and magnetic fields from the stellar explosions that make up the pulsar. The team finds that these magnetic fields can accelerate electrons to even higher energies, and that if those electrons slam into ambient photons, they can convert those particles of light into ultrahigh energies, turning them into gamma rays. can.

“Pulsars are certainly very powerful accelerators,” Fang says, “in many places where particle acceleration can occur.”

And this can lead to a bit of confusion. Gamma-ray telescopes have very poor vision. For example, LHASSO can only extract details as small as half the size of the full Moon. So the gamma-ray sources that telescopes detect tend to look like blob or bubbles, d’Ona Wilhelmy says. There may be several energetic sources within those droplets, which are unresolved to current observatories.

“With better angular resolution and better sensitivity, we should be able to identify whether” [and] where the accelerator is,” she says. Some future observatories — like the Cherenkov Telescope Array and the Southern Wide-field Gamma-ray Observatory — can help, but they are many years out.

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