HAVE the first stars finally revealed themselves? Astronomers in the US are
claiming they may have found clusters that contain the first generation of stars
to have congealed out of the cooling debris of the big bang. 鈥淚f we鈥檙e right,
it鈥檚 an awesome discovery,鈥� says Chris Churchill of Pennsylvania State
University in University Park.
After the blinding explosion of the big bang, the Universe was completely
dark for a billion years. Then lights began to switch on. These first stars
would have been the building blocks of today鈥檚 galaxies, but no one knows what
they looked like or how they formed.
Churchill and his colleagues Jane Rigby of the University of Arizona in
Tucson and Jane Charlton of Penn State were measuring radiation from distant
quasars, noticing which wavelengths of light had been absorbed along the way to
Earth, when they found clouds of hydrogen, magnesium and iron floating in space
between us and the quasars. Heavy elements such as magnesium and iron are only
formed in stars.
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The team did not see the stars directly, but found the clusters were
tiny鈥攁bout 30 light years across or just a ten-thousandth the size of a
galaxy like the Milky Way.
The chances of such small objects being between us and any quasar are very
slim. For the astronomers to have found any, there must be huge numbers of gas
clouds. 鈥淲e are talking about a million times more than normal galaxies,鈥� says
Churchill. Since the clouds are so small and numerous, the team suspect they
could be the building blocks of galaxies. 鈥淚t鈥檚 such a remarkable result that we
delayed publication, trying everything under the sun to get away from it.鈥�
In a paper to be published in The Astrophysical Journal, the team
suggests that the mysterious gas clouds were the first objects to form in the
Universe鈥攃lusters of so-called Population III stars. Until now, no one has
ever detected any sign of these ancient ancestors. Seeing them is the principal
goal of NASA鈥檚 Next Generation Space Telescope, planned for launch this decade.
To see them as they were forming, NGST will look for objects whose light has
taken 13 billion years to reach us. But the gas clouds detected by Churchill and
his colleagues are closer. 鈥淲e are not seeing the clusters when they formed but
a billion or so years later, when many [stars] have exploded,鈥� says Rigby.
Bernard Pagel of the University of Sussex says the objects鈥� small size is
reminiscent of predictions made in 1968 of what the first star clusters might
look like. 鈥淚n that case, they might indeed be associated with Population III
stars,鈥� he says. But astrophysicist Abraham Loeb of Harvard University is more
sceptical. 鈥淭he most likely origin of these clouds, in my view, would be
progenitors of ordinary globular star clusters.鈥�
But if the team is right, knowing that the first clusters were 30 light years
across and contained around 100,000 stars, for example, would help astronomers
to work out how they must have formed. Churchill thinks the clusters they found
never got incorporated into galaxies. That means they should still be around
today, even lurking in our own neighbourhood. Such fossil star clusters would be
very faint, most of their stars having gone out or faded to dim, red embers.
Churchill and his team are planning to use the Hubble Space Telescope to look
for them.