NASA’s famous Voyager spacecraft have made the first detection of cosmic ray electron bursts accelerated by shock waves that originate from large eruptions on the Sun.
The detection, reported by a team of physicists led by the University of Iowa, occurred when the Voyagers – which left Earth in 1977 – they keep walking away through interstellar space, making them the first ships to record this unique physics in the realm among the stars.
These newly detected bursts of electrons are like an accelerated forward guard along the magnetic field lines in the interstellar medium; electrons travel almost at the speed of light, about 670 times faster than the shock waves that initially propelled them. The explosions were followed by plasma wave oscillations caused by lower-energy electrons that reached Voyager’s instruments days later, and eventually, in some cases, the shock wave itself up to a month later.
Shockwaves emanated from coronal mass ejections, hot gas and energy ejections moving outward from the sun at about a million miles per hour. Even at those speeds, shock waves take more than a year to arrive to the Voyager spacecraft, which has moved farther from the Sun (over 14.5 billion miles and counting) than any human-made object.
“What we see here specifically is a certain mechanism whereby when the shock wave first contacts the interstellar magnetic field lines that traverse the spacecraft, reflects and accelerates some of the electrons in cosmic rays“says Don Gurnett, emeritus professor of physics and astronomy at Iowa and corresponding author of the study, published in The Astronomical Journal.
“We have identified through cosmic ray instruments that these are electrons that were reflected and accelerated by interstellar collisions that propagate outward from energetic solar events on the Sun. That is a new mechanism“, has added.
The discovery could help physicists better understand the dynamics behind shock waves and cosmic radiation from erupting stars (whose brightness may vary 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 that far exceed those we experience on Earth.
Physicists believe that these electrons in the interstellar medium they are reflected in a reinforced magnetic field at the edge of the shock wave and are subsequently accelerated by the movement of the shock wave. The reflected electrons then spin in a spiral along the lines of the interstellar magnetic field, gaining speed as the distance between them and the impact increases.
In a 2014 article in the magazine 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 analyzes electron explosions detected by the Voyager spacecraft that are believed to be accelerated by a similar process.
“The idea that shock waves accelerate particles is not new,” Gurnett said. “It all has to do with how it works, the mechanism. And the fact that we detect it in a new realm, the interstellar medium, which is very different from the solar wind where similar processes have been observed. No one’s seen him with an interstellar shock wave, in a completely new pristine environment, “he added.