THE fireball of the big bang may have expanded faster in some places than
others, says a team of astronomers in Italy. They think this would explain why
there are mysterious giant voids in the Universe where few galaxies roam.
Astronomers have struggled to understand why galaxies seem to be grouped in
shells around huge voids millions of light years across. Our own Galaxy is on
the edge of such a void.
One possible reason for the voids is that the fireball that filled the
Universe shortly after the big bang did not expand evenly. Some areas may have
expanded much faster than others, leaving the fireball riddled with 鈥渃osmic
产耻产产濒别蝉鈥�.
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However, many scientists have been reluctant to accept this, having failed to
find the footprints of these irregularities in the microwave background
radiation鈥攖he sea of radiation left over from the fireball after it
cooled.
But now a study by Luca Amendola, Franco Occhionero and their colleagues at
the Astronomical Observatory of Rome suggests that a pattern of ripples in the
background radiation may be hiding the hallmarks of small cosmic bubbles. These
ripples, discovered by NASA鈥檚 COBE satellite in 1992, mark density fluctuations
in the early Universe. 鈥淭his works as long as the bubbles weren鈥檛 too large at
that time,鈥� says Amendola.
The team鈥檚 analysis will appear later this year in Monthly Notices of the
Royal Astronomical Society. Amendola adds that analysis of data from existing
experiments could resolve the issue over the next couple of years.
Max Tegmark, a cosmologist at the University of Pennsylvania, stresses that
the analysis doesn鈥檛 prove cosmic bubbles ever existed. He suspects that the
voids in the Universe are simply random patterns left by the violent expansion
of a fairly smooth, bubble-free young Universe. 鈥淚 don鈥檛 think there鈥檚 any
evidence that we need more than the standard recipe,鈥� he says.