January 12, 2005

Unit of Measurement for Expanding Universe

SAN DIEGO, California (AFP) -- Astrophysicists have drawn up the largest map to date of the universe, confirming gravity's role in its formation and establishing an accurate way of measuring its expansion, according to studies presented at a meeting of the American Astronomical Society.

Daniel Eisenstein, a University of Arizona scientist said the observations made by two internatioal teams of scientists showed the universe was flat, expanding and marked by ripples caused by the shock waves of the "Big Bang" -- the cataclysmic explosion that created the universe some 14 million years ago.

The way galaxies are currently distributed throughout the cosmos is directly related to the shock waves that gave it birth, Eisenstein told a press conference on the sidelines of the AAS convention that will end Thursday in San Diego.

"We regard this as smoking-gun evidence that gravity has played the major role in growing from the initial seeds in the microwave background into the galaxies and clusters of galaxies that we see around us," he said.

"These sound waves left their imprint in the Cosmic Microwave Background, remnant radiation from the Big Bang seen when the universe was 400,000 years old," he added.

"We are now seeing the corresponding cosmic ripples in the SDSS galaxy maps" -- Sloan Digital Sky Survey that has mapped 46,000 galaxies spread out over a distance of four billion light years. The two international teams have mapped some 260,000 galaxies.

"These ripples in the matter grew for a million years until the universe cooled enough to freeze them in place," said astrophysicist Bob Nichol, with the Cosmology and Gravitation Institute of Britain's University of Portsmouth.

"What we now see in the SDSS galaxy data is the imprint of these ripples billions of years later," Nichol added.

The scientists said the distance between each ripple can be used to measure the universe's rate of expansion.

The two teams of researchers, chiefly from Australia, Britain and the United States, have determined that galaxy formation occurrs at every 500 million light year interval, matching exactly the intervals between the Big Bang shock wave ripples observed when the cosmos was young.

A light year is the distance traveled in a year by a light wave moving at 300,000 kilometers (186,000 miles) per second. In numbers it is equivalent to 9,461 billion kilometers, or 6,000 billion miles.

The fact that the universe is flat, as the observations of the international teams have confirmed, also lends support to the theory of the expanding universe, said Eisenstein.

It represents a period of very rapid expansion the universe underwent a fraction of a second after the Big Bang.

The observations also tend to confirm the notion that the matter we are familiar with forms only a small fraction of the universe, with the rest made up of mysterious or "black" matter and energy, the scentists said.