Scientists find traces of ‘cosmic dawn’
In the beginning there was a hot cloud of darkness. Hundreds of thousands of years passed before the first atoms of hydrogen and helium began to stick together. Then, suddenly, the hydrogen collapsed into the first stars in the universe and there was light.
The moment the universe was illuminated has been observed for the first time through the ‘‘silhouette’’ it left in ancient radio waves zipping around the cosmos at a frequency that is partly blotted out by BBC Radio 2.
At a desert observatory in Western Australia scientists rigged up a glorified FM antenna and pointed it at the night sky. The resulting discovery, published in the journal Nature, could change the course of physics. For one thing, it tells us that the ‘‘cosmic dawn’’ of the earliest stars occurred less than 180 million years after the Big Bang.
More importantly, it threatens to overthrow established theories of ‘‘dark matter’’, which is estimated to be about four times more abundant than the ordinary sort but has yet to be detected.
The trouble is that the universe seems to have been much chillier in its youth than anyone thought. ‘‘If that idea is confirmed, then we’ve learnt something new about the mysterious dark matter that makes up 85 per cent of the matter in the universe,’’ Judd Bowman, an astronomer at Arizona State University and the paper’s lead author, said.
‘‘This would provide the first glimpse of physics beyond the standard model."
Viewed through the lens of a radio telescope, the sky is saturated with billions of microwaves left over from the aftermath of the Big Bang, known as the Cosmic Microwave Background (CMB). Dr Bowman and his team discovered that at a certain frequency, this signal dips because some of the CMB was soaked up by free-floating hydrogen atoms that had been warped by ultraviolet radiation from the first stars.
This terrestrial noise can be 10,000 times more powerful than the faint echoes of newborn galaxies that the scientists are trying to detect, according to Peter Kurczynski, who oversaw the US National Science Foundation’s funding for the project. ‘‘It’s like being in the middle of a hurricane and trying to hear the flap of a hummingbird’s wing,’’ he said.
Rennan Barkana, the head of astrophysics at Tel Aviv University in Israel, said that dark matter could be to blame. Up to now, dark matter has usually been evoked as a kind of gravitational glue holding galaxies together.
Professor Barkana thinks that it might have somehow stolen some of the heat emitted by the first stars, although this would mean that scientists have to redefine their understanding of what dark matter is.
The signals from cosmic dawn may also be our best opportunity to show that it really exists.