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Getting heavy

点击量:   时间:2019-03-07 03:09:04

By Robert Adler DID the fireball of the early Universe cook up a much richer cocktail than anyone realised? A German astrophysicist is challenging the idea that the early Universe created only hydrogen, helium and lithium. He thinks it may also have made heavier elements such as carbon. The standard big bang theory suggests that a soup of quarks in the early Universe condensed to form the nuclei of hydrogen, helium and lithium around 100 seconds after the big bang. After that, the cooling fireball was no longer hot enough to support the synthesis of heavier elements such as carbon, which didn’t appear until stars formed and made them in their cores. But around 10 years ago, scientists speculated that heavier elements could have formed just after the big bang if the Universe wasn’t uniform but was filled with dense clumps of quark trios, or baryons. The nuclear reactions in these lumps would run faster, so heavier elements such as carbon would have time to form before the temperature became too low. However, the theory had a flaw: it predicted that the fireball would leave far more lithium-7 behind than we see. But now Karsten Jedamzik of the Max Planck Institute in Garching, Germany, has solved this problem. Jedamzik and his colleagues have shown that theoretically, tiny particles called neutrinos in the fireball would heat baryon clumps and make them expand, halting heavy element production at just the right level. “The region expands, the baryon density goes down, and when it reaches a certain value, the process shuts off,” says Jedamzik. Some elements as heavy as carbon would be left over, along with just the amounts of lithium-7 that are observed. Jedamzik doesn’t know why the lumps would have formed. The transition of matter from a soup of free quarks to nuclear particles could have done this. But his idea may explain one puzzle—gas floating between galaxies seems to contain more heavy elements than it should. “Astronomers have not been able to find primordial, heavy-element-free material left over from the big bang,” says Leo Blitz, an astrophysicist at the University of California at Berkeley. Keith Olive, a cosmologist at the University of Minnesota, remains sceptical. “It’s interesting he could get enhanced carbon,” he says. He thinks the idea might be confirmed if astronomers find the stars that formed from this early gas and see if they indeed have heavy elements in their outer atmospheres. But it will always be difficult to prove that there aren’t other stars with only the lightest elements, he adds. Michael Turner of the University of Chicago thinks the idea is still worth checking out. “The light elements are like fossils. They give us a window on the Universe when it was a second old and let us ask profound questions about the forces of nature.” But Jedamzik, whose theory has not yet been published, admits that the odds are against his idea. “The fruit may not be hanging there,” he says. “But if it is,