Astrophysicists simulate comet X-ray emissions in laboratory

LIVERMORE, Calif. — Physicists from the Lawrence Livermore National Laboratory have produced X-ray emissions in a laboratory setting by recreating the conditions that exist when solar winds collide with gases surrounding comets.

Using the electron beam ion trap facility located at Livermore Laboratory, physicists Peter Beiersdorfer, Hui Chen and Mark May created charge exchange between heavy ions to produce X-ray emissions, similar to what happens when solar wind and gases collide in a comet.

In collaboration with researchers from NASA Goddard Space Flight Center, Columbia University Department of Physics and the University of Missouri-Rolla Department of Physics, the team will present “Laboratory Simulation of Charge Exchange-Produced X-ray Emission From Comets” in the June 6 edition of Science.

The researchers studied charge exchange-induced cometary X-ray emissions by installing the spare X-ray microcalorimeter spectrometer (XRS) from the ASTRO-E satellite mission onto Livermore’s existing electron beam ion trap. The XRS was designed to view distant objects such as supernova remnants with a higher spectral resolution than is available at the Chandra X-ray Observatory.

Beiersdorfer said that cometary X-rays can serve as a diagnostic for solar activity and hence “space weather” by measuring the quantity and composition of the heavy ion flux in solar wind. In addition, recent work has shown that emissions can be a potential tool to gauge the speed of the solar wind.

“Because comets enter the solar system from different directions in and out of the ecliptic, they probe regions that are not covered by spacecraft,” he said.

Cometary X-ray emissions form when a continuous stream of charged heavy ions in the solar wind collide with the gases surrounding the nucleus of a comet.. The collision is believed to neutralize the solar wind ions and induce them to give off X-rays characteristic of the ions and gases involved in the collision.

Actual X-ray emissions have been observed at the Chandra X-ray Observatory. In the Livermore experiments, the Goddard microcalorimeter recorded X-ray data that explained the emission seen from comets in the solar system.

“Next to the Sun, the process we demonstrated here at Livermore makes comets the strongest X-ray emitters in the solar system,” Beiersdorfer said.