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Rare Earth element found in ancient stars

Washington, Wed, 22 Feb 2012 ANI

Washington, Feb 22 (ANI A team of researchers from institutions including MIT has for the first time detected traces of element tellurium- which is very rare on Earth - in three ancient stars that are nearly 12 billion years old.

 

For the past 50 years, scientists have been analysing stars of various ages, looking to chart the evolution of chemical elements in the universe and to identify the astrophysical phenomena that created them.

 

The finding supports the theory that tellurium, along with even heavier elements in the periodic table, likely originated from a very rare type of supernova during a rapid process of nuclear fusion.

 

"We want to understand the evolution of tellurium - and by extension any other element - from the Big Bang to today," said Anna Frebel, an assistant professor of astrophysics at MIT and a co-author of the study.

 

"Here on Earth, everything's made from carbon and various other elements, and we want to understand how tellurium on Earth came about."

 

The team analysed the chemical composition of three bright stars located a few thousand light-years away, "in the halo of the Milky Way," Frebel relates.

 

The researchers looked at data obtained from the Hubble Space Telescope's spectrograph, an instrument that splits light from a star into a spectrum of wavelengths. If an element is present in a star, the atoms of that element absorb starlight at specific wavelengths; scientists can observe this absorption as dips in the spectrograph's data.

 

Frebel and her colleagues detected dips in the ultraviolet region of the spectrum - at a wavelength that matched tellurium's natural light absorption - providing evidence that the rare Earth element does indeed exist in space, and was likely created more than 12 billion years ago, at the time when all three stars formed.

 

The researchers also compared the abundance of tellurium to that of other heavy elements such as barium and strontium, finding that the ratio of elements was the same in all three stars.

 

Frebel said the matching ratios support a theory of chemical-element synthesis: namely, that a rare type of supernova may have created the heavier elements in the bottom half of the periodic table, including tellurium.

 

According to theoretical predictions, elements heavier than iron may have formed as part of the collapsing core of a supernova, when atomic nuclei collided with huge amounts of neutrons in a nuclear fusion process. For 50 years, astronomers and nuclear physicists have modeled this rapid process, named the r-process, in order to unravel the cosmic history of the elements.

 

Frebel's team found that the ratios of heavy elements observed in the three stars matched the ratios predicted by these theoretical models. The findings, she said, confirm the theory that heavier elements likely formed from a rare, extremely rapid supernova.

 

"You can make iron and nickel in any ordinary supernova, anywhere in the universe. But these heavy elements seem to only be made in specialized supernovas. Adding more elements to the observed elemental patterns will help us understand the astrophysical and environmental conditions needed for this process to operate," Frebel added.

 

Jennifer Johnson, an associate professor of astronomy at Ohio State University, says tellurium has been a "tough" element to detect, since it absorbs light in the ultraviolet spectrum, which is impossible for ground-based telescopes to spot.

 

The team's findings, she says, are a first step in identifying some of the most elusive elements in the universe.

 

The researchers published their findings online in Astrophysical Journal Letters. (ANI)

 


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