For the first time ever, astronomers from NASA and the University of Tübingen in Germany have detected rare noble gases krypton and xenon in the spectrum of a hot white dwarf.

Discovered in 1898 by Sir William Ramsay and Morris Travers, krypton (Kr) and xenon (Xe) are two of the rarest elements on Earth. They were formed with all the other elements billions of years ago by earlier generations of stars.

Astronomers assume that they were synthesized during the supernovae of very heavy stars and in stars of mid-range mass like our Sun.

Until recently, there was no spectroscopic proof of krypton or xenon from the Sun or other stars – although astronomers detected krypton in interstellar space. It was assumed it occurred with the same frequency in the Sun and other stars.

Finding a star with measurably higher krypton (and xenon) frequency would demonstrate that both elements were formed there. That is exactly what the team has done – finding these elements in a white dwarf.

The astronomers using NASA’s Far Ultraviolet Spectroscopic Explorer, or FUSE, have observed the burnt-out star RE 0503-289.

They were able to identify and analyze absorption lines in the ultraviolet spectrum, showing that Kr and Xe occur hundreds and thousands of times more often. That is a clear indicator that they were formed there. The results, published in the Astrophysical Journal Letters, confirm one of the predicted birthplaces of these gases.

From the time of its discovery in 1994, the DO white dwarf RE 0503-289 has attracted attention of the astronomers because it belongs to the rare subclass of white dwarfs which show no trace of hydrogen – the most common element in stars.

Along with krypton and xenon, the team observing RE 0503-289 also detected highly ionized photospheric lines from other trans-iron group elements, namely gallium, germanium, arsenic, selenium, molybdenum, tin, tellurium and iodine, from which gallium and molybdenum are also new discoveries in white dwarfs.

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Bibliographic information: Klaus Werner et al. 2012. First detection of krypton and xenon in a white dwarf. ApJ 753 L7; doi: 10.1088/2041-8205/753/1/L7