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鈥檛
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鈥檛 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.
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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. 鈥淭he region expands,
the baryon density goes down, and when it reaches a certain value, the process
shuts off,鈥� 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鈥檛 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鈥攇as floating between galaxies seems to
contain more heavy elements than it should. 鈥淎stronomers have not been able to
find primordial, heavy-element-free material left over from the big bang,鈥� says
Leo Blitz, an astrophysicist at the University of California at Berkeley.
Keith Olive, a cosmologist at the University of Minnesota, remains sceptical.
鈥淚t鈥檚 interesting he could get enhanced carbon,鈥� 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鈥檛 other stars with only the
lightest elements, he adds.
Michael Turner of the University of Chicago thinks the idea is still worth
checking out. 鈥淭he 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.鈥�
But Jedamzik, whose theory has not yet been published, admits that the odds
are against his idea. 鈥淭he fruit may not be hanging there,鈥� he says. 鈥淏ut if it
is, it鈥檚 very big.鈥�