In the interiors of brown dwarfs or gaseous planets, among other places, is a mysterious state of matter with a temperature of a few thousand degrees and a high density, close to that of a solid. Although common in the Universe, it is very difficult to produce and analyze in the laboratory.
A new era in experimental research of this so-called warm dense matter (WDM) state began just a dozen years ago, when physicists launched the first free-electron X-ray lasers. At the forefront of this type of device is the 3.4 km (2.1 mile) long European XFEL laser.
A series of experiments recently carried out there made it possible to observe for the first time how quickly a metal transforms into the exotic state of ionized WDM to become transparent (non-absorbing) to X-rays at the end of the process. The achievement of the international team of scientists – including those from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow – is discussed in a paper published in the journal Nature Physics.
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