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Carlos Frenk: Dark matter
 real 28k

Carlos Frenk: Why we did it
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Friday, 29 January, 1999, 10:22 GMT
Universe put on the map
This 3D map charts 15,500 galaxies and is
This 3D map charts 15,500 galaxies and is "one of the great maps of history"
by BBC News Online's Science Editor Dr David Whitehouse

Astronomers have produced the largest-ever map of the cosmos, which they say answers some of our deepest questions about the universe.

"It is by far the biggest map of anything. There is nothing like it in its scale," said Professor Carlos Frenk of Durham University in the UK, one of the cosmic cartographers.

The new map has taken 10 years to compile and covers a sphere of radius 700 million light years, each of which is six million million miles.

While this is a gigantic region of space in human terms it represents only a small fraction of the universe, about one ten thousandth.

Despite this scientists think it is representative of the entire cosmos. "We have finally mapped a representative region of the universe," said Prof Frenk.

Map of history

Using an all-sky survey carried out by the now spent Infra-Red Astronomical Satellite (IRAS), an international team of astronomers have charted the positions of 15,500 galaxies.

Plotting them in a three-dimensional map has produced the largest region ever mapped.

"When we first got this map from the computer we were thrilled," says Prof Frenk, "We knew it was one of the great maps of history."

RAS sky survey data
IRAS sky survey data
The main features of the map are superclusters of galaxies. Galaxies, star systems like our own, occur in clusters ranging from a few dozens to a few thousands of galaxies.

These clusters are themselves grouped into galactic superclusters which can be seen on the map.

Astronomers are especially interested in the voids between the superclusters.

"They really are voids," says Prof Frenk, "they are not completely free of galaxies but they are far rarer than in the superclusters."

An important aspect of the map is the ratio of the size of the superclusters to the size of the voids. This is believed to be something fundamental about the make-up of the universe.

The map contains encoded information about the matter that makes up the universe. The sizes of the superclusters are determined by the force of gravity coming from the universe's mysterious "dark matter".

"The structures we see are sculpted by the most important force in the universe, gravity," adds Prof Frenk. "We can use it to determine what the dark matter is as well as the fate of the universe itself."

From the distribution of matter in the map scientists think that the universe will expand forever.

Last of its kind

According to astronomers this is the last map of its kind for a generation. To make it required an infra-red (IR) survey of the sky. Only IR light can peer far enough into the cosmos to produce such maps.

At the moment there are no plans for a larger, more sensitive IR satellite than IRAS. It will be more than a decade before there is another one.

A 'deep-core' view of the universe
A deep-core view of the universe
What astronomers will be doing, however, is looking far deeper into space in certain directions. One current Anglo-Australian project is charting the positions of 250,000 galaxies in one small patch of sky.

"It is an historic map," remarks Prof Frenk. "Some day it will be hanging from every kid's wall."

If it does perhaps there will be an arrow pointing to the very centre of the map along with the caption, "we are here".

Throughout history our view of the world has been governed by maps. Greek maps, of which none survive, were said to show nothing beyond the basin of the Mediterranean.

Medieval "mappaemundi" expanded mankind's horizons and frequently called uncharted regions terra incognita.

Driven by the need of trade and conquest our world was mapped some 200 years ago, about the time we began finding new planets in our solar system.

Since then we have charted the positions of the nearest stars and discovered that we live in a galaxy, one of many carried along in expanding space.

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09 Jun 98 | Sci/Tech
New maps of the sky unveiled
02 Dec 98 | Sci/Tech
Moon map aids discovery
01 Dec 98 | Sci/Tech
Through a cosmic lens
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