Fresh light on dark energy

   A new study into the mysterious force called dark energy may reassure
   cosmologists that the Universe is not going to be ripped apart.

   Researchers at the U.S. Space Telescope Science Institute in Baltimore
   said they had found more evidence for dark energy, which may make up
   70% of the universe.

   The researchers will publish their results in the Astrophysical Journal. 

   Dark energy was discovered only six years ago and may hold the key to the
   future of the universe, depending on how strong and how permanent it is. 

   It is thought to behave in the opposite way to gravity. Rather than
   pulling galaxies together, it pushes them apart.

   The only way cosmologists can try to learn about dark energy is
   through indirect observations. They use the Hubble Space Telescope
   to look at the oldest, most distant supernovae they can find, and
   measure the light coming from them. 

   This light would have left the exploding stars billions of years ago and
   its colour, known as red shift, tells astronomers about how fast they
   were accelerating at the time. This gives clues about the expansion of
   the universe and its age. 

   "In 1998 we first detected that the universe was accelerating and was
   apparently being driven to that state by this very mysterious dark
   energy that appears to make up 70% of the universe," said the
   institute's Dr Adam Reiss. "That took us all by surprise. We don't
   really understand what it is." 

   No more stars in the sky

   One hope is that dark energy is the explanation for Albert Einstein's
   theoretical cosmological constant, a number that will predict whether
   the universe will collapse in a "big crunch", be completely blown apart
   in a "big rip" or just drift steadily until the galaxies are so far apart
   they cannot be seen, in effect taking the stars from the sky. 

   "Right now we're about twice as confident than before that Einstein's
   cosmological constant is real, or at least dark energy does not appear
   to be changing fast enough [if at all] to cause an end to the universe
   anytime soon," Reiss added. 

   "If Einstein was right and dark energy remains at the strength it is for
   all time, the Universe will expand forever," Reiss said.

   Monday, 23 February 2004

   http://www.abc.net.au/science/news/stories/s1051237.htm

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