A galactic fossil

May 10, 2007

How old are the oldest stars" Using ESO's VLT, astronomers recently measured the age of a star located in our Galaxy. The star, a real fossil, is found to be 13.2 billion years old, not very far from the 13.7 billion years age of the Universe. The star, HE 1523-0901, was clearly born at the dawn of time.

"Surprisingly, it is very hard to pin down the age of a star", the lead author of the paper reporting the results, Anna Frebel, explains. "This requires measuring very precisely the abundance of the radioactive elements thorium or uranium, a feat only the largest telescopes such as ESO's VLT can achieve."

This technique is analogous to the carbon-14 dating method that has been so successful in archaeology over time spans of up to a few tens of thousands of years. In astronomy, however, this technique must obviously be applied to vastly longer timescales.

For the method to work well, the right choice of radioactive isotope is critical. Unlike other, stable elements that formed at the same time, the abundance of a radioactive (unstable) isotope decreases all the time. The faster the decay, the less there will be left of the radioactive isotope after a certain time, so the greater will be the abundance difference when compared to a stable isotope, and the more accurate is the resulting age.

Yet, for the clock to remain useful, the radioactive element must not decay too fast - there must still be enough left of it to allow an accurate measurement, even after several billion years.

"Actual age measurements are restricted to the very rare objects that display huge amounts of the radioactive elements thorium or uranium," says Norbert Christlieb, co-author of the report.

Large amounts of these elements have been found in the star HE 1523-0901, an old, relatively bright star that was discovered within the Hamburg/ESO survey [1]. The star was then observed with UVES on the Very Large Telescope (VLT) for a total of 7.5 hours.

A high quality spectrum was obtained that could never have been achieved without the combination of the large collecting power Kueyen, one of the individual 8.2-m Unit Telescopes of the VLT, and the extremely good sensitivity of UVES in the ultraviolet spectral region, where the lines from the elements are observed.

For the first time, the age dating involved both radioactive elements in combination with the three other neutron-capture elements europium, osmium, and iridium.

"Until now, it has not been possible to measure more than a single cosmic clock for a star. Now, however, we have managed to make six measurements in this one star"," says Frebel.

Ever since the star was born, these "clocks" have ticked away over the eons, unaffected by the turbulent history of the Milky Way. They now read 13.2 billion years.

The Universe being 13.7 billion years old, this star clearly formed very early in the life of our own Galaxy, which must also formed very soon after the Big Bang.
More Information

This research is reported in a paper published in the 10 May issue of the Astrophysical Journal ("Discovery of HE 1523-0901, a Strongly r-Process Enhanced Metal-Poor Star with Detected Uranium", by A. Frebel et al.).

The team includes Anna Frebel (McDonald Observatory, Texas) and John E. Norris (The Australian National University), Norbert Christlieb (Uppsala University, Sweden, and Hamburg Observatory, Germany), Christopher Thom (University of Chicago, USA, and Swinburne University of Technlogy, Australia), Timothy C. Beers (Michigan State University, USA), Jaehyon Rhee (Center for Space Astrophysics, Yonsei University, Korea, and Caltech, USA).


[1]: The Hamburg/ESO sky survey is a collaborative project of the Hamburger Sternwarte and ESO to provide spectral information for half of the southern sky using photographic plates taken with the now retired ESO-Schmidt telescope. These plates were digitized at Hamburger Sternwarte.


Related Uranium Articles from Brightsurf:

Russian scientists suggested a transfer to safe nuclear energy
Scientists from Far Eastern Federal University (FEFU), Ozersk Technological Institute, and the Russian Academy of Sciences have improved a processing technology of a monazite concentrate which is a mineral raw material employed as a source of rare earth elements and thorium.

Story tips: Molding matter atom by atom and seeing inside uranium particles
Story tips from the Department of Energy's Oak Ridge National Laboratory: Molding matter atom by atom and seeing inside uranium particles

Atomic fingerprint identifies emission sources of uranium
Depending on whether uranium is released by the civil nuclear industry or as fallout from nuclear weapon tests, the ratio of the two anthropogenic, i.e. man-made, uranium isotopes 233U and 236U varies.

Old molecule, new tricks
Fifty years ago, scientists hit upon what they thought could be the next rocket fuel.

Unused stockpiles of nuclear waste could be more useful than we might think
Chemists have found a new use for the waste product of nuclear power -- transforming an unused stockpile into a versatile compound which could be used to create valuable commodity chemicals as well as new energy sources.

Uranium chemistry and geological disposal of radioactive waste
A new paper to be published on Dec. 16 provides a significant new insight into our understanding of uranium biogeochemistry and could help with the UK's nuclear legacy.

Laser-produced uranium plasma evolves into more complex species
When energy is added to uranium under pressure, it creates a shock wave, and even a tiny sample will be vaporized like a small explosion.

Using building materials to monitor for high enriched uranium
A new paper details how small samples of ubiquitous building materials, such as tile or brick, can be used to test whether a facility has ever stored high enriched uranium, which can be used to create nuclear weapons.

Uranium toxicity may be causing high rates of obesity and diabetes in Kuwait
Kuwait has some of the highest rates of obesity and diabetes in the world, and scientists don't know why.

Bio-inspired material targets oceans' uranium stores for sustainable nuclear energy
Scientists have demonstrated a new bio-inspired material for an eco-friendly and cost-effective approach to recovering uranium from seawater.

Read More: Uranium News and Uranium Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.