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Monday, 11 November, 2002, 17:02 GMT
Universe 'mostly made of dark energy'
SDSS
A quasar: Very distant but one of the brightest objects in the sky
International scientists say they have gathered fresh data which suggests most of the energy in the Universe is likely to be in an invisible and presently unknown form.

Using the world's most powerful telescopes to make radio pictures of thousands of distant quasars - some of the brightest objects in the sky - the scientists calculated that two thirds of the cosmos is made up of dark energy.

The findings fit in with current thinking as astronomers have calculated that the total mass of all the visible galaxies only makes up about one-third of the critical density needed to satisfy the best current theory about the early Universe.

Fermilab Visual Media Services
The research tallies with large galaxy surveys
It may also explain what is causing the expansion of the Universe to accelerate.

Dark energy seems to push the very fabric of space apart causing the Universe to expand ever faster.

The most convincing evidence came from recent measurements of distant supernovae which showed that the Universe is indeed expanding with increasing pace.

However dark energy only affects the properties of the Universe over very large distances - like exploding stars in far away galaxies - and so it is very difficult to measure using current technology.

Independent evidence

These latest observations were made as part of a 10-year study using gravitational lenses.

Dark energy
Einstein's General Theory of Relativity allows for the existence of dark energy
It is a property of empty space that causes the Universe to expand more and more rapidly
Dark energy only shows up in observations which probe significant fractions of the observable Universe
Gravitational lensing - first predicted by Albert Einstein - allows scientists to probe distant parts of the Universe in greater detail than would normally be possible.

Very massive objects such as neutron stars have gravitational fields so intense that they actually bend light coming from further away.

The process magnifies, brightens and distorts images of the distant quasars, and acts like a powerful "zoom lens" for viewing regions of the Universe that are so far away they could not normally be observed with the largest available telescopes.

Dr Ian Browne, of the University of Manchester, Jodrell Bank Observatory, UK, one of the astronomers behind the research, said: "The new gravitational lens test is based on completely different physical arguments to the previous ones and so provides independent evidence in support of dark energy."

The research is published in Physical Review Letters.

See also:

11 Jul 01 | Science/Nature
14 Apr 00 | Science/Nature
19 Feb 00 | Science/Nature
20 Jan 00 | Science/Nature
10 Dec 98 | Science/Nature
26 May 99 | Science/Nature
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