February 21, 2012
Rare Earth Element Discovered In Ancient Stars
A team of researchers say they have discovered that a rare Earth element known as tellurium exists in three ancient stars that are nearly 12 billion years old.
The new discovery helps support the theory that the element, along with even heavier elements in the periodic table, likely originated from a rare type of supernova.
"We want to understand the evolution of tellurium – and by extension any other element – from the Big Bang to today," Anna Frebel, an assistant professor of astrophysics at MIT and a co-author on the paper, said in a recent press release. "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 analyzed the chemical composition of three bright stars located a few thousand light-years away in the halo of the Milky Way.
They looked at data obtained by the Hubble Space Telescope's spectrograph. This instrument splits light from a star into a spectrum of wavelengths.
The team detected dips in the ultraviolet region of the spectrum, providing evidence that the rare Earth element does exist in space, and was likely created over 12 billion years ago.
The team compared the abundance of tellurium to that of other heavy elements like barium and strontium, finding that the ratio of elements was the same in all three stars.
Frebel said the matching ratios help support the theory of chemical-element synthesis. According to this theory, a rare type of supernova may have created the heavier elements in the bottom half of the periodic table.
Theoretical predictions show that elements heavier than iron may have formed as part of the collapsing core of a supernova, a time when atomic nuclei collided with huge amounts of neutrons in a nuclear fusion process.
Astronomers and nuclear physicists have modeled this process for 50 years, unraveling the cosmic history of the elements.
The team found that the ratios of heavy elements observed in the three stars matched the ratios predicted by these theoretical models.
Frebel said the findings 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," Frebel said. "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."
Jennifer Johnson, an associate professor of astronomy at Ohio State University, said tellurium has been tough to detect because it absorbed light in the ultraviolet spectrum.
She said that the team's findings are the first step in identifying some of the most elusive elements in the universe.
"If you look at the periodic table, tellurium is right in the middle of these elements that are hard for us to measure," Johnson said. "If we need to understand how [the r-process] works in the universe, we really have to measure this part of the periodic table. It's really cool that they got this element in this sea of unknown-ness."
The researchers published their findings online in Astrophysical Journal Letters.
On the Net: