Scientists finally solved mystery of why comets emit X-rays

The mystery of how comets are able to emit X-rays has been solved by a team led by the University of Oxford.

The mystery of how comets are able to emit X-rays has been solved by a team led by the University of Oxford. Image credit: Shutterstock
The mystery of how comets are able to emit X-rays has been solved by a team led by the University of Oxford. Image credit: Shutterstock

When comets travel through the Solar System they interact with Solar radiation, the Solar wind, and the Solar magnetic field. This produces an obvious climate or ‘coma’ and in addition the watched cometary tail, and sometimes, X-rays. These are created on the Sun-ward side of the comet where the Solar breeze impacts the cometary climate, shaping a bow shock.

To figure out how this X-rays are generated, a team of scientists from 15 institutes, including the Universities of Arizona, Belfast, Copenhagen, Chicago, Lisbon, London, Osaka, Oxford, Paris, Strathclyde, Taiwan, as well as AWE Aldermaston, ETH Zurich, RAL Chilton, , performed experiments at the LULI laser facility in Paris, where they replicated the interaction of the Solar wind with a comet.

A problem that is especially confusing, given that such outflow is typically connected with extremely hot articles like the Sun, and comets are among the oldest questions in the Solar System.

The exploration uncovered that when this plasma stream impacts onto a strong sphere, the research facility ‘comet’ (put about a centimeter far from the plastic thwart), it takes after what happens when a genuine comet goes through the Solar system. It was discovered that electrons are warmed to around a million degrees in the up-stream locale by plasma turbulence.

These hot electrons are in charge of radiating X-beams within the sight of an attractive field.

Electron acceleration in laboratory bow shock Image credit: F. Cruz and L. O. Silva, IST Lisbon, Portugal
Electron acceleration in laboratory bow shock Image credit: F. Cruz and L. O. Silva, IST Lisbon, Portugal

Alexandra Rigby, an Oxford University student who is doing her doctoral work on the project and led the experiment said: “The laser beams are fired onto a plastic foil which explodes, causing a stream of electrons and ions to be expelled forming a high-speed flow of ionised gas (plasma) like the Solar wind.”

Professor Gianluca Gregori from the University of Oxford said, “These experimental results provide direct laboratory evidence that objects moving through magnetized plasmas can be sites of electron heating. This process is common in astrophysics and can take place not only in comets, but also in planetary magnetospheres (as of our own Earth), or even in supernova remnants where the ejected material sends a shock wave into the interstellar gas’.”

Moreover, the study enlightens another cosmic mystery, how high energy particles are generated in Nature. It occurs due to plasma turbulence can provide the initial source of fast particles in, supernova shock waves.

Professor Sarkar said: “As a theorist I find it amazing that it is possible to sensibly replicate astrophysical phenomena in the laboratory, to test our physical understanding of how cosmic particle accelerators may work.”

The research published in Nature Physics.