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 expansion 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 in 1995 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).

To download images click here.

For more information or interview:
Dr Brian Schmidt, Mount Stromlo Observatory, ANU 02 6125 8042 or email:
brian@mso.anu.edu.au
or Clarissa Thorpe, ANU Public Affairs 02 6125 5575 (w) or 0416 249 245(mobile)

No:30/2001

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Last Modified Tue, July 16, 2002