At https://phys.org/news/2019-12-interstellar-comet-2iborisov-sun.html … telescopes around the world have been focussed on Comet Borisov, the apparent interstellar visitor. It is moving so fast it has not been captured by our Sun, yet still sports a tail of dust and debris.
At www.sci-news.com/physics/comets-emit-x-rays-05820.html … physicists claim to have solved the riddle of comets emitting X-rays. When comets travel through the solar system they interact with solar radiation, the solar wind, and the solar magnetic field. This induces a visible atmosphere around the comet (the coma) and the observed cometary tail. In some cases it also produces X-rays.
The authors of the study in Nature Physics (see https://doi.org/0.1038/s41567-018-0059-2 ) did an experiment by firing a laser beam on to a plastic foil, which exploded, causing a stream of electrons and ions to be expelled – creating a high speed flow of plasma (just like the solar wind). This plasma flow then impacted onto a solid sphere (a laboratory version of the comet) and electrons heated up to around one million degrees as a result of plasma turbulence. These hot electrons were responsible for emitting X-rays, we are told (but only in the presence of a magnetic field). Note also the laboratory comet was represented by a solid sphere. An experiment rather than a model simulation. Good.