The Big Bang forged only three elements — hydrogen, helium, and a little bit of lithium — the lightest and simplest elements of all. Stars formed from these elements, and converted some of them into heavier elements, such as carbon, oxygen, and iron.
Astronomers have searched in vain for a star or gas cloud made solely of the three elements from the Big Bang — they all contain at least a small amount of heavier material.
But they recently discovered two gas clouds that seem to be primordial — they contain no detectable heavy elements at all. One cloud is in Leo, the lion, while the other’s in Ursa Major, the great bear. The clouds are more than 11 billion light-years away, so we see them as they were only about two billion years after the Big Bang.
Both clouds are dark. Astronomers found them only because the clouds happen to lie in front of even more distant quasars — extremely bright galaxies that were common in the early universe.
Different elements in the gas clouds reveal their presence by absorbing light from the quasars. But the only element that could be seen was hydrogen, which was made in the Big Bang. From this, the astronomers deduce that the clouds have no more than about one ten-thousandth as much heavy elements as the Sun does.
The discovery indicates that even two billion years after the Big Bang, some regions remained pristine — their composition unaltered from the time of the birth of the universe.
Script by Ken Croswell, Copyright 2012
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