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Embargoed to Tuesday 3 April, 2001

Supernova shines light on mysterious 'dark energy'

New research using the NASA Hubble Space Telescope could prove the theory
that the universe is accelerating. Dr Brian Schmidt from The Australian
National University's Mount Stromlo Observatory is part of an international
team of astronomers using the Hubble Telescope to study the depths of
space.

The US-Australian team has focused on a distant supernova observed in 1997.
The exploding star is 10 billion light years away, and is the most distant
supernova ever observed. Comparing Hubble observations taken in1995 with
images taken in 1997 revealed this most distant explosion.

The burst of light from the farthest exploding star could boost the case
for the existence of a mysterious form of 'Dark Energy' making galaxies
move ever faster away from each other. "This far-flung stellar detonation
called a supernova, happened 10 billion years ago when the universe was
only about one-quarter its present age, at a time before gravity lost its
grip and the universe began accelerating. Now 'Dark Energy' is dominating
the cosmic struggle and is driving the Universe apart," Dr Brian Schmidt
said.

"This supernova shows us the universe is behaving like a driver who slows
down as he approaches a red stoplight and then hits the accelerator when
the light turns green," says project leader, Adam Riess
of the Space  Telescope Science Institute (STScI) in Baltimore, Maryland."

This supernova is a special class of explosion that allows astronomers to
measure the cosmological expansion very accurately. "By measuring how
bright the explosion appears on Earth, we are able to deduce how many light
years the supernova is in distance," Dr Schmidt said. "We can also measure
how fast the object is moving away from us by seeing how red its light has
been stretched by the expanding universe.

In 1998, two teams, one lead by Schmidt and one based in the US, revealed,
using the Hubble telescope and powerful ground-based telescopes that
galaxies were flying apart at a faster rate today than long ago. Some
theorist believe that they are seeing a new feature of Einstein's theory of
gravity, that some matter can be repulsive.

"Because the exploding star is so far away it offers the first tantalizing
observational evidence that gravity was once slowing down the Universe's
expansion, but now has been overcome by a repulsive form of matter or'Dark
Energy'," Dr Schmidt said.

The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc.(AURA) for NASA, under contract
with the Goddard Space Flight Center, Greenbelt, MD.  The Hubble Space
Telescope is a project of international cooperation between NASA and the
European Space Agency (ESA).

Images can be downloaded from: http://msowww.anu.edu.au/~brian/PRESS/

For more information or interview:
Dr Brian Schmidt, Mount Stromlo Observatory, ANU +612 6125 8042 or email:
brian@mso.anu.edu.au
or Clarissa Thorpe, ANU Public Affairs +612 6125 5575 (w) or 0416 249
245(mobile)

No:30/2001