Photograph by A. Rizzi, DEA/De Agostini/Getty Images
The zirconium-rich star in an artist's impression. Illustration courtesy Natalie Behara
Published December 8, 2010
There's a star in the sky that sparkles like a diamond—thanks to vast amounts of zirconium in its atmosphere, astronomers have announced.
Dubbed LS IV-14 116, the faint, blue star lies about 2,000 light-years from the sun. Detailed new measurements reveal the star to be the most zirconium-rich known to date, with levels more than 10,000 times higher than those in our sun.
While real diamonds are made of carbon, jewellers make false diamonds out of zirconium dioxide crystals, aka cubic zirconia. The mineral zirconium silicate, or zircon, is also widely used as a gemstone. (Related: "'Diamond Planets' Hint at Dazzling Promise of Other Worlds.")
In addition to zirconium, astronomers studying LS IV-14 116 found chemical signatures for high amounts of three other elements rarely seen in stellar atmospheres: strontium, germanium, and yttrium.
"It really is quite an oddball," said team member Simon Jeffery of Armagh Observatory in Northern Ireland.
An In-Between Star
Jeffery and colleagues found the high amount of zirconium while studying the chemistry of LS IV-14 116. Previous measurements had indicated the star is a rare, helium-rich hot subdwarf.
When less massive stars die, they swell up and start shedding their outer layers of gas, becoming red giants. When all the gas is released, the leftover core of the dead star is called a white dwarf.
Hot subdwarfs represent a phase of evolution for some stars that comes between red giants and white dwarfs, so studying them will give scientists greater insight into how stars live and die. (Related: "Red Giant Sun May Not Destroy Earth.")
Using the Anglo-Australian Telescope at Siding Spring Observatory in New South Wales, the team took a closer look at LS IV-14 116's spectral lines, the frequencies of light emitted by the star, as determined by the elements and molecules present.
The spectral line for zirconium was not only strong, it corresponded to a form of the metal that exists only at temperatures above 20,000 degrees Celsius. This form had previously never been seen in any astronomical object.
More Zirconium Stars Out There?
Based on models of the star's atmosphere, the team concluded that the four unusual elements are clustered in thin clouds around the star, which have settled out in layers according to their masses.
Normally radiation emitted by the star would churn the elements in the star's atmosphere. But this star is cooling very slowly, and there are few external influences.
"The atmosphere is very still on these kinds of star, with little mixing occurring," Jeffery said.
As the temperature of the star changes, however, so too does the level of radiation, meaning that atmospheric elements will move to new levels to keep in balance with the radiation. These changes will take many thousands of years, the scientists suspect.
Previous studies had shown that two other oddball stars have high abundances of elements not often seen in stellar objects, including nickel, iron, and vanadium. Jeffery and his colleagues speculate that these stars may be at different stages in the cooling and sorting process.
Overall, the team believes that such stars are very unusual.
"There are likely to be a few more in our galaxy, but they may well be too faint to be seen," he said. "We are now on the lookout for more zirconium stars, with bigger telescopes."
The zirconium-rich star is described in a paper slated to appear in the Monthly Notices of the Royal Astronomical Society. A preprint of the paper is available online at the Cornell University website arXiv.org.
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