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Last Updated: Wednesday, 12 January, 2005, 11:05 GMT
Sky surveys reveal cosmic ripples
By Jonathan Amos
BBC News science reporter

Galaxy flythrough (AAO)
In one sense, this work explains why we are here
The unimaginably big of today has its explanation in the fantastically small of 13 billion years ago.

Astronomers have shown how the present pattern of galaxies in the cosmos grew from tiny fluctuations in the density of matter just after the Big Bang.

The work draws on results from two scientific teams conducting sky surveys based in Australia and the US.

"It's an amazing new insight into how the Universe works," said Prof Carlos Frenk, of the University of Durham, UK.

"These are two teams separated by many thousands of miles that are completely independent - they have one member in common - and they have both, using different techniques and different data, arrived at the same conclusion," he told the BBC News website.

We've taken a simple theory and we've produced these incredibly detailed and beautiful observations and it all matches
John Peacock, University of Edinburgh
The teams announced the breakthrough jointly in London and in San Diego, at the American Astronomical Society meeting.

It essentially explains why we are here - why matter created in the Big Bang came together to create everything we see around us.

And the researchers hope the advance will lead to a new understanding of dark matter and dark energy, phenomena that dominate the Universe but whose true nature is a mystery.

Smallest scale

The findings come out of giant, three-dimensional maps of near space produced by the Two Degree Field Galaxy Redshift Survey (2dFGRS), which has a robotic telescope in New South Wales; and the Sloan Digital Sky Survey (SDSS), which uses an observatory in New Mexico.

These maps trace the structure of matter in the current Universe. They show, for example, how the clustering of galaxies is strung into vast filaments and sheets and separated by great voids.

Temperature fluctuations in the microwave background (Nasa)
About 380,000 years after the Big Bang, matter and radiation "decoupled"
Matter went on to form stars and galaxies; radiation spread out and cooled
Radiation now shines in microwave portion of the electromagnetic spectrum - at a very cold -270.45 deg Celsius
By mapping the tiniest temperature fluctuations (mottled colours above) in CMB, astronomers can "see" the distribution of matter in the early Universe
Now, statistical analysis of these map data has revealed how this distribution of matter has taken a particular course that was influenced by forces that were at work at the dawn of time.

What is more, the "fingerprint" left by this influence is exactly the same as that already seen in the remnant heat from the Big Bang - the cosmic microwave background (CMB) radiation - by the Cobe and WMap space telescopes in 1992 and 2003.

This ancient light, which pervades the sky in all directions, is now a frigid minus 270.45 Celsius. Even so, it contains tiny - one part in 100,000 - deviations in its temperature profile that theory suggests reflect subtle density differences in the matter of the early Universe.

The new statistical work demonstrates how these small differences would have evolved under the pull of gravity to draw the matter into the groupings of galaxies, stars and planets we see in the sky today.

"At the moment of birth, the Universe contained tiny irregularities, thought to have resulted from quantum, or subatomic processes," explained Dr Shaun Cole, from the University of Durham, and lead 2dFGRS investigator.

"These irregularities have been amplified by gravity ever since and eventually gave rise to the galaxies we see today."

Simple but true

The fingerprint takes the form of pressure waves or sound waves - "acoustic peaks" or "baryon wiggles" as the scientists call them - which have nudged matter on its very discrete course.

Its most obvious manifestation is the startling discovery that there is a slight excess of galaxies with separations of 500 million light-years.

"Cosmic web" - the structure of matter in the Universe (AAO)
On the largest scales, matter is organised into filaments and sheets
"We've been told for years that galaxies originated in the quantum fluctuations coming out of the first few seconds of the Universe - these galaxies have grown through gravitational collapse and that's all that was needed," recalled Prof Bob Nichol, an SDSS co-worker at the University of Portsmouth.

"Today, we have striking evidence that that is exactly what happened. It seems to be that simple."

And Prof John Peacock, the 2dFGRS UK team leader from the University of Edinburgh, added: "It is amazing to me that we've taken a simple theory and we've produced these incredibly detailed and beautiful observations and it all matches. It's everything you could wish for as a scientist."

Both the Sloan and 2dFGRS teams say the work has given them a new "yardstick" with which to determine distances in the Universe and the rate at which the cosmos is expanding.

Normal vs dark

Central to this will be the investigation of dark matter and dark energy.

The former is made from material unknown to science and invisible to current telescope technology. Its existence was only discovered because of the effect its gravity has on galaxies.

The even more mysterious dark energy is believed to emerge from the vacuum of empty space. It acts as an anti-gravity force that is driving galaxies apart from one another at an accelerating rate.

The 2.5m reflecting telescope of the Sloan Digital Sky Survey (SDSS)
Sloan uses a 2.5m telescope at Apache Point Observatory in New Mexico
"The amazing thing about all these results is that they are in perfect accord with the predictions of the standard cosmological model, including dark matter and dark energy," said Prof Daniel Eisenstein, of the University of Arizona, and lead SSDS investigator.

"So while it all fits together it sill leaves us 'in the dark' about the nature of these two mysterious components which dominate the energy of the Universe."

The 2dFGRS team says its analysis has enabled the Universe to be weighed with unprecedented accuracy: it turns out that normal, or "baryonic", matter, including all the galaxies, stars and planets, makes up only 18% of all the mass in the cosmos, with the remaining 82% accounted for by dark matter.

The Sloan group says its work has given the clearest demonstration yet that the geometry of the Universe is "flat".

This means the usual rules of Euclidean geometry taught in schools apply all over the cosmos: straight lines can be extended to infinity and the angles of a triangle add up to 180 degrees, etc.

The 2dFGRS findings are being published in the Monthly Notices of the Royal Astronomical Society. The results from the SDSS were submitted for publication in the Astronomical Journal in December.

Mission's path to new astronomy
24 Jun 04 |  Science/Nature
Dark energy tops science class
20 Dec 03 |  Science/Nature
Universe to expand for ever
14 Feb 03 |  Science/Nature
A 'gift of galaxies'
29 Jun 01 |  Science/Nature
Galaxy survey solves cosmic riddle
08 Mar 01 |  Science/Nature
Voyage through the Universe
19 May 00 |  Science/Nature

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