The Voyager spacecraft detects a new type of solar electron explosion

More than 40 years after its launch, the Voyager probe is still making discoveries.

In a new study, a team of physicists led by the University of Iowa reports the first detection of electron bursts of cosmic rays accelerated by shockwaves originating from large solar flares. The detection, carried out by instruments aboard the Voyager 1 and Voyager 2 spacecraft, took place as the Voyagers continue their outward journey through interstellar space, thus making them the first aircraft to record this unique physics in the realm among the stars.

These newly detected flashes of electrons are like an accelerated advance guard along the magnetic field lines in the interstellar medium; electrons travel at nearly the speed of light, about 670 times faster than the shock waves that initially propelled them. The explosions were followed by oscillations in the plasma wave caused by low-energy electrons arriving at the Voyager instruments days later – and finally, in some cases, the shock wave itself up to a month later.

Shockwaves are emanated from coronal mass ejections, ejections of hot gas and energy that move outward from the sun at approximately one million miles per hour. Even at those speeds, it takes more than a year for the shock waves to reach the Voyager spacecraft, which has traveled farther from the sun (more than 14 billion miles and beyond) than any man-made object.

“What we see specifically here is a certain mechanism whereby when the shock wave first comes into contact with the lines of the interstellar magnetic field passing through the spacecraft, it reflects and accelerates some of the electrons of the cosmic rays, ”says Don Gurnett, professor emeritus of physics and astronomy in Iowa and the corresponding author of the study. “We have identified through cosmic ray instruments these are electrons that have been reflected and accelerated by interstellar shocks that propagate outward from energetic solar events to the sun. This is a new mechanism.”

The discovery could help physicists better understand the dynamics behind shockwaves and cosmic radiation emanating from flare stars (which can vary in brightness briefly due to violent activity on their surface) and exploding stars. It would be important to consider the physics of such phenomena when sending astronauts on extended lunar or Martian excursions, for example, during which they would be exposed to concentrations of cosmic rays far in excess of those we experience on Earth.

Physicists believe that these electrons in the interstellar medium are reflected by a strengthened magnetic field at the edge of the shock wave and subsequently accelerated by the motion of the shock wave. The reflected electrons then spiral along the lines of the interstellar magnetic field, gaining speed as the distance between them and the shock increases.

In a 2014 article in the journal Astrophysical Letters, physicists JR Jokipii and Jozsef Kota theoretically described how ions reflected by shock waves could be accelerated along the lines of the interstellar magnetic field. The current study examines the electron bursts detected by the Voyager probe that are thought to be accelerated by a similar process.

“The idea that shock waves accelerate particles is not new,” Gurnett says. “It all has to do with how it works, the mechanism. And the fact that we detected it in a new realm, the interstellar medium, which is very different from the solar wind where similar processes have been observed. Nobody has seen it. an interstellar shock wave, in a completely new and uncontaminated medium “.

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The results were published online in Astronomical Journal, in a paper entitled “A Foreshock Model for Interstellar Shocks of Solar Origin: Voyager 1 and 2 Observations”.

Co-authors include William Kurth of Iowa; Edward Stone and Alan Cummings of the California Institute of Technology; Bryant Heikkila, Nand Lal, and Leonard Burlaga of NASA’s Goddard Space Flight Center; Stamatios Krimigis and Robert Decker of the Johns Hopkins University Applied Physics Laboratory; and Norman Ness of the University of Delaware.

NASA funded the research.