Astrophile: Blinged-out stars were born rich
Objects: Ancient stars
Composition: Chock-full of heavy metal
At first glance, CS 22892-052 looks like a run-of-the-mill old star. Born about 13 billion years ago, only 700 million years after the big bang, it is lacking in many of the shinier, more interesting elements. But look closer, and you’ll see that this stellar granny is adorned with gold.
Now Terese Hansen of the Neils Bohr Institute in Copenhagen, Denmark, and colleagues think they’ve figured out why. Long ago, a jet of neutrons could have sprinkled gold into this lucky star’s nursery.
Stars usually show their ages in their clothes. Very old stars tend to be austere, sticking to the simpler, lighter elements because they condensed from pristine clouds of hydrogen and helium gas created in the big bang.
Younger stars are threaded with heavier metallic elements, such as copper and zinc. These elements are formed by massive stars, which spew their contents into nearby gas clouds to be incorporated into the next generation.
Yet about 3 to 5 per cent of aged stars are decked out in some of the heavy elements of the young. CS 22892-052 was the first known example of such a blinged-out old star in the Milky Way. Strangely, while they don’t have much of the middleweight stuff such as iron or cobalt, they have plenty of the heaviest elements, including gold, platinum and lead.
These elements can only be formed in a type of nuclear reaction called the r-process, thought to happen in supernova explosions, when a powerful blast of neutrons rapidly bulks up atomic nuclei. “That tells us that those stars are probably witnesses to whatever astrophysical process gave us the r-process,” says Timothy Beers of Michigan State University in East Lansing.