A small corner of the universe, yesterday
An international team of astronomers have produced the first map of our universe as it was 11 billion years ago, filling the cartographic gap from the Big Bang and the rapid expansion that came after.
Published in the Journal Astronomy & Astrophysics, the study shows that the universe actually started to slow in its expansion roughly three billion years after the Big Bang. This slow expansion occurred prior to the force of so-called 'dark energy', a force which sent galaxies accelerating away from each other.
There is ample knowledge of the immediate conditions after the Big Bang as found in studies of the universes afterglow in the cosmic background radiation. The universes’ accelerating expansion over several billion years can be seen with a look at the way distant galaxies are moving.
Dr. Mat Pieri of the Institute of Cosmology and Gravitation at the University of Portsmouth (Britain), has said: "Only now are we finally seeing its adolescence... just before it underwent a growth spurt."
There is sparse knowledge on dark energy, and its counterpart dark matter, in the physics community but astronomers argue the force must exist in order to account for the speed at which the universe is expanding. Taken together, dark energy and dark matter are believed to make up about 96 per cent of the universe.
The pioneering study supports the theory that dark energy was somehow created as the universe expanded. This study claims this is demonstrated by detailing a period when gravity was winning the tussle and slowing the expansion.
Dr. Pieri went on to say: "If we think of the universe as a roller coaster, then today we are rushing downhill, gaining speed as we go. Our new measurement tells us about the time when the universe was climbing the hill - still being slowed by gravity."
The 63 scientists from 9 different countries that produced the cosmic map did so by using a novel technique. They are now studying the intense light from 50,000 distant quasars as it passes through clouds of hydrogen in space on its way to Earth.
The technology produces a picture of the ancient universe in same way thousands of flashlight beams would light up a hillside of fog.
"The quasars are back-lights," Dr. Pieri said. The gas in front of the back-lights absorbs a fraction of the light which allows astronomers to develop a detailed picture of distant clouds of gas. This distant cloud is known as the “intergalactic medium.”
The map is the result of a five-year project begun in 2009. From the third Sloan Digital Sky Survey, the team expect to expand the survey with light from about 160,000 quasars by the end of the project.
"We're essentially measuring the shadows cast by gas along a series of lines, each billions of light-years long," said Prof. Will Percival, colleague of Dr. Pieri, at the University of Portsmouth.
"The tricky part is combining all those one-dimensional maps. The problem is like trying to recognize an object from a picture that's been painted on the quills of a porcupine," Prof. Percival concluded.
