Roughly 13.8 billion years ago, in a moment believed to have occurred faster than the speed of light, our universe was born — a point we refer to as the big bang.
While the universe began as hot and opaque, as it rapidly expanded, it first became dark and cold, lasting for about 400,000 years. There was little else in the universe other than hydrogen gas, its most abundant element.
Eventually stars formed and over hundreds of millions of years, galaxies. But that “eventually” nagged astronomers: when exactly did the first stars form?
Now, a team of scientists believe they’ve found a signal in the darkness, the first hint of stars emerging from the primordial soup that created everything we know.
In the beginning…
Astronomers have theorized that some time between 100 million to 700 million years following the big bang, gravity slowly pulled together dense regions of hydrogen gas. As these clumps became denser, they collapsed in upon themselves, creating fusion, and the first stars were born.
Ultraviolet radiation from these stars, astronomers also believed, would interact with hydrogen gas, which in turn absorbed some cosmic microwave background radiation left over from the big bang. This allowed hydrogen to be seen, as a type of shadow detectable in particular radio frequencies.
Scientists around the world have been looking for that telltale sign of the first stars emerging. The time at which this occurred is referred to as the Epoch of Reionization (EoR). And now researchers at Arizona State University and the Massachusetts Institute of Technology (MIT) together with the National Science Foundation in the United States, believe they’ve found it.
Back in time
When we look up at the night sky, we see stars as they were, not as they are. That’s due to the time it takes light to travel (300,000 kilometres a second). Even the light from the sun takes eight minutes to reach us.
We use the speed of light when measuring vast distances in the universe like the space between stars and galaxies. For example, the nearest star to Earth is Proxima Centauri, 4.2 light-years away.
There are no optical telescopes to look back in time. The farthest we’ve seen is through the eyes of the Hubble Space Telescope, some 13.4 billion years back.
So instead of visually looking for the first stars, astronomers listen using radio telescopes, then look for a signal in the data.
Listening is no easy task. The universe is a noisy place — at least in the form of static — not to mention the noise that we produce locally.
To make things even more difficult for researchers, astronomers were expecting to hear the signal in a radio band that is commonly used here on Earth.
“There is a great technical challenge to making this detection,” Peter Kurczynski, the NSF program director said.
“Sources of noise can be 10,000 times brighter than the signal. It’s like being in the middle of a hurricane and trying to hear the flap of a hummingbird’s wings.”
After searching for a location that would be relatively quiet, the researchers settled on the Murchison Radio-astronomy Observatory (MRO) in Western Australia.
There, they set up what looks like nothing more than a dining room table: the Experiment to Detect the Global EoR Signature (EDGES).