An international team of astronomers has just released the first results from a study that began in 2009: a map of the Universe just three billion years after the Big Bang — when it was in its adolescence — just before it experienced the 'growth spurt' attributed to Dark Energy.
"If we think of the universe as a roller coaster, then today we are rushing downhill, gaining speed as we go," said Dr Matthew Pieri, one of the authors of the study, who is a Marie Curie Research Fellow at the University of Portsmouth in Britain. "Our new measurement tells us about the time when the universe was climbing the hill — still being slowed by gravity."
When we look out into the universe, we are seeing backward in time. This is due to the limit of the speed of light. The farther away something is, the farther the light from it had to travel to reach us, so when we look at objects in space now, we are seeing them as they were in the past. Thus, at any particular moment we look up into the sky, we are seeing the Sun as it was just over 8 minutes ago, we are seeing the stars that make up the Alpha Centauri system — the closest star system to our own — as they were a little over 4 years ago, we are seeing the centre of our galaxy — The Milky Way — as it was around 27 thousand years ago, and so on.
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By using telescopes and tracking a specific section of the night sky for long periods of time, astronomers can gather more and more light from that section, like when a photographer takes a long-exposure picture and is able to gather more and more detail about their subject. This allows them to see fainter and fainter objects, and ones that are further and further away and thus we see those objects as they were further and further back in time.
The research, conducted by 63 scientists from 9 different countries (and posted online here), shows a time when gravity was winning out against the initial forces that cause the universe to expand. By examining this time period closely, they can gather clues as to what may have generated the dark energy that caused the Universe to expand, and which continues to make the Universe expand, faster and faster, all the time.
In this third survey of the night sky, which will take approximately 5 years to complete, they are using light from about 160,000 quasars — the supermassive black holes at the cores of incredibly ancient galaxies — to peer through the hydrogen that makes up the 'interstellar medium'.
"We're essentially measuring the shadows cast by gas along a series of lines, each billions of light-years long," said Dr Will Percival, Professor of Cosmology 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," he added.