Radioactive thorium in another galaxy
This is M32, an example of a dwarf elliptical galaxy. Credit: 1.1 Meter Hall Telescope, Lowell Observatory, Bill Keel (U. Alabama)
COS 82 is an orange giant star in a dwarf elliptical galaxy located 220,000 light-years away, in the direction of the constellation Ursa Minor. In 2007, astronomers discovered thorium in this star.
The discovery in 2007 of the heaviest element ever seen in a distant galaxy – thorium – should let astronomers begin to use a new technique for finding the ages of stars in other galaxies.
They’ll do this in the same way geologists measure the age of rocks: via radioactive dating. Radioactive thorium decays over time. So the older a rock – or a star – the less thorium it’ll have. By comparing the amount of thorium with the abundance of other elements, scientists can figure out the ages of rocks or stars.
Japanese astronomers looked at the star COS 82 in a small galaxy external to our own Milky Way. Analysis of its light revealed the element thorium and let astronomers date this star. Their rough estimate of 13 billion years placed COS 82 in the same age range as the oldest stars in our galaxy.
The uncertainty in the estimate is high, and the astronomers admit they could be off on this star’s age by as much as 6 billion years. Now they want to search for another radioactive element – uranium – within this very distant star. That will help them pinpoint the accuracy to just 2 billion years – quite a feat for a star outside our Milky Way’s boundaries.
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Since stars first start with Hydrogen and fuse it until element 92, then it would seem logical that copper is made in a sun.