Voyager spacecraft detects new type of solar electron burst

More than 40 years after their launch, the Voyager spacecraft is still making discoveries.

In a new study, a team of physicists led by the University of Iowa reports the first detection of bursts of cosmic-ray electrons accelerated by shock waves from major flares on the sun. The detection, carried out by instruments aboard the Voyager 1 and Voyager 2 spacecraft, occurred as the Travelers continue their outward journey through interstellar space, making it the first spacecraft to record this unique physics in the realm between the stars.

These newly detected electron bursts are like advanced protection accelerated along magnetic field lines in the interstellar medium; electrons travel at almost the speed of light, about 670 times faster than the shock waves that initially propelled them. The bursts were followed by oscillations of plasma waves caused by low-energy electrons arriving at the Travelers’ instruments a few days later – and finally, in some cases, by the shock wave itself up to a months after that.

The shock waves emanated from coronal mass ejections, expulsions of hot gas and energy that travel outward from the sun at about a million miles per hour. Even at these speeds, it takes more than a year for shock waves to reach the Voyager spacecraft, which has traveled farther from the sun (over 14 billion kilometers or more) than any object made by the Sun. ‘man.

“What we are seeing here specifically is a certain mechanism by which, when the shock wave first makes contact with the interstellar magnetic field lines passing through the spacecraft, it reflects and accelerates some of the electrons from 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 propagating outward from solar energy events in the sun. This is a new mechanism.”

The discovery could help physicists better understand the dynamics behind shock waves and cosmic radiation from cob stars (whose brightness can change briefly due to violent activity on their surface) and exploding stars. The physics of these phenomena would be important to consider when sending astronauts on extended lunar or Martian excursions, for example, during which they would be exposed to concentrations of cosmic rays far exceeding what 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 then accelerated by the motion of the shock wave. The reflected electrons then coil along interstellar magnetic field lines, 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 from shock waves could be accelerated along interstellar magnetic field lines. The current study looks at the bursts of electrons detected by the Voyager spacecraft that would be accelerated by a similar process.

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

###

The results were published online in the Astronomical journal, in an article entitled “A Foreshock Model for Interstellar Shock 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 from NASA’s Goddard Space Flight Center; Stamatios Krimigis and Robert Decker of the Applied Physics Laboratory at Johns Hopkins University; and Norman Ness of the University of Delaware.

NASA funded the research.