BY MEASURING the positions of a staggering 106 688 galaxies and their
distances away from us, an international team of astronomers has produced a
three-dimensional mega-map of a swathe of the Universe with a volume of 13
billion billion billion cubic light years. Their estimate of the mass of this
material supports a growing consensus that the Universe will continue expanding
for ever.
Using the Two-degree Field (2dF) spectrograph at the Anglo-Australian
Telescope in New South Wales, the team estimated the distances to the fleeing
galaxies by measuring their red shifts: the stretching of light waves due to the
expansion of the Universe. The map was built by combining the red shifts with
the positions of the galaxies in the sky.
The new map covers 5 per cent of the sky and reaches out 4 billion light
years into deep space. It shows large numbers of clusters and superclusters of
galaxies, and huge voids that are relatively empty of stars. No structures are
much larger than a few hundred million light years across, says team member
Gavin Dalton of Oxford University.
Advertisement
The 2dF team was also able to determine the total mass, both visible and
invisible, in the volume they surveyed. According to Dalton, they estimate from
this that the Universe contains only 40 per cent of the mass needed for gravity
to stop the current expansion. 鈥淭his implies that our Universe will expand for
ever,鈥� he says.
Meanwhile, the Sloan Digital Sky Survey鈥攁 similar survey based in the
northern hemisphere, at Apache Point Observatory in New Mexico鈥攑lans to
measure 1 million galaxy red shifts in five years. 鈥淲e鈥檒l catch up with 2dF in
about a year and a half,鈥� says Andy Connolly of the University of Pittsburgh in
Pennsylvania.
