Hexbyte Glen Cove Process leading to supernova explosions and cosmic radio bursts unearthed at PPPL

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Physicist Kenan Qu with figures from his paper. Credit: Photo of Qu by Elle Starkman/PPPL Office of Communications. Collage by Kiran Sudarsanan.

A promising method for producing and observing on Earth a process important to black holes, supernova explosions and other extreme cosmic events has been proposed by scientists at Princeton University’s Department of Astrophysical Sciences, SLAC National Acceleraor Laboratory, and the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL). The process, called quantum electrodynamic (QED) cascades, can lead to supernovas—exploding stars—and fast radio bursts that equal in milliseconds the energy the sun puts out in three days.

First demonstration

The researchers produced the first theoretical demonstration that colliding a laboratory laser with a dense electron beam can produce high-density QED cascades. “We show that what was thought to be impossible is in fact possible,” said Kenan Qu, lead author of a paper in Physical Review Letters (PRL) that describes the breakthrough demonstration. “That in turn suggests how previously unobserved collective effects can be probed with existing state-of-the-art laser and electron beam technologies.”

The process unfolds in a straightforward manner. Colliding a strong laser pulse with a high energy electron beam splits a vacuum into high-density electron-positron pairs that begin to interact with one another. This interaction creates what are called collective plasma effects that influence how the pairs respond collectively to electrical or magnetic fields.

Plasma, the hot, charged state of matter composed of free electrons and atomic nuclei, makes up 99 percent of the visible universe. Plasma fuels fusion reactions that power the sun and stars, a process that PPPL and scientists around the world are seeking to develop on Earth. Plasma processes throughout the universe are strongly influenced by electromagnetic fields.

The PRL paper focuses on the electromagnetic strength of the laser and the energy of the electron beam that the theory brings together to create QED cascades. “We seek to simulate the conditions that create electron-positron pairs with sufficient density that they produce measurable collective effects and see how to unambiguously verify these effects,” Qu said.

The tasks called for uncovering the signature of successful plasma creation through a QED process. Researchers found the signature in the shift of a moderately intense laser to a higher frequency caused by the proposal to send the laser against an electron beam. “That finding solves the joint problem of producing the QED plasma regime most easily and observing it most easily,” Qu said. “The amount of the shift varies depending on the density of the plasma and the energy of the pairs.”

Beyond current capabilities

Theory previously showed that sufficiently strong lasers or electric or magnetic fields could create QED pairs. But the required magnitudes are so high as to be beyond current laboratory capabilities.

However, “It turns out that current technology in lasers and relativistic beams [that travel near the speed of light], if co-located, is sufficient to access and observe this regime,” said physicist Nat Fisch, professor of astrophysical sciences and associate director for academic affairs at PPPL, and a co-author of the PRL paper and principal investigator of the project. “A key point is to use the laser to slow down the pairs so that their mass decreases, thereby boosting their contribution to the plasma frequency and making the collective effects greater,” Fisch said. “Co-locating current technologies is vastly cheaper than building super-intense lasers,” he said.

This work was funded by grants from the National Nuclear Security Administration and the Air Force Office of Scientific Research. Researchers now are gearing up to test the theoretical findings at SLAC at Stanford University, where a moderately strong is being developed and the source of electrons beams is already there. Physicist Sebastian Meuren, a co-author of the paper and a former post-doctoral visitor at PPPL who now is at SLAC, is centrally involved in this effort.

“Like most fundamental physics this research is to satisfy our curiosity about the universe,” Qu said. “For the general community, one big impact is that we can save billions of dollars of tax revenue if the theory can be validated.”

More information:
Kenan Qu et al, Signature of Collective Plasma Effects in Beam-Driven QED Cascades, Physical Review Letters (2021). DOI: 10.1103/PhysRevLett.127.095001

Process leading to supernova explosions and cosmic radio bursts unearthed at PPPL (2021, October 5)

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Hexbyte Glen Cove Fast radio bursts shown to include lower frequency radio waves than previously detected thumbnail

Hexbyte Glen Cove Fast radio bursts shown to include lower frequency radio waves than previously detected

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A burst from the periodically active repeating fast radio burst source 20180916B arrives at the LOFAR telescope. The higher frequency radio waves (purple) arrive earlier than the lower frequency radio waves (red). The inset shows an optical image from the host galaxy of the fast radio burst source and the position of the source in the host galaxy. Credit: Futselaar / ASTRON / Tendulkar

Since fast radio bursts (FRBs) were first discovered over a decade ago, scientists have puzzled over what could be generating these intense flashes of radio waves from outside of our galaxy. In a gradual process of elimination, the field of possible explanations has narrowed as new pieces of information are gathered about FRBs—how long they last, the frequencies of the radio waves detected, and so on.

Now, a team led by McGill University researchers and members of Canada’s CHIME Fast Radio Burst collaboration has established that FRBs include radio waves at frequencies lower than ever detected before, a discovery that redraws the boundaries for theoretical astrophysicists trying to put their finger on the source of FRBs.

“We detected down to 110 MHz where before these bursts were only known to exist down to 300 MHz,” explained Ziggy Pleunis, a postdoctoral researcher in McGill’s Department of Physics and lead author of the research recently published in the Astrophysical Journal Letters. “This tells us that the region around the source of the bursts must be transparent to low-frequency emission, whereas some theories suggested that all low-frequency emission would be absorbed right away and could never be detected.”

The study focussed on an FRB source first detected in 2018 by the CHIME radio telescope in British Columbia. Known as FRB 20180916B, the source has attracted particular attention because of its relative proximity to Earth and the fact that it emits FRBs at regular intervals.

The research team combined the capacities of CHIME with those of another radio telescope, LOFAR, or Low Frequency Array, in the Netherlands. The joint effort not only enabled the detection of the remarkably low FRB frequencies, but also revealed a consistent delay of around three days between the higher frequencies being picked up by CHIME and the lower ones reaching LOFAR.

“This systematic delay rules out explanations for the periodic activity that do not allow for the frequency dependence and thus brings us a few steps closer to understanding the origin of these mysterious bursts,” adds co-author Daniele Michilli, also a postdoctoral researcher in the Department of Physics at McGill.

More information:
Z. Pleunis et al, LOFAR Detection of 110–188 MHz Emission and Frequency-dependent Activity from FRB 20180916B, The Astrophysical Journal Letters (2021). DOI: 10.3847/2041-8213/abec72

Fast radio bursts shown to include lower frequency radio waves than previously detected (2021, April 16)
retrieved 17 April 2021
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