Last updated March 5, 2018 at 11:27 am
Astronomers have detected signals from what could be some of the first stars ever created, and these signals may tell us more about the nature of dark matter.
Astronomers have potentially just answered one of the big questions about the birth of the universe.
They’ve detected some of the first light from some of the first stars ever to form. And not only that, they could have revealed some of the mysteries of dark matter while they were at it.
The signals are so old they come from even further back in time than the Hubble Space Telescope has been able to detect – originating only 180 million years after the Big Bang.
Around this time, the universe was just beginning to emerge from the so-called “Dark Ages”, a time where the universe cooled and went dark for millions of years.
In the darkness, gravity pulled matter together until stars formed and burst into life, bringing the “cosmic dawn”. This new-found signal marks the closest astronomers have seen to that moment – the earliest ever detection of a signal from a developing universe.
It fills in one of the missing gaps in the story of how the Big Bang led to existence as we know it.
A discovery made in Australia
Once stars began to form in the early universe, their light is thought to have excited a massive cloud of hydrogen gas.
This excited gas then began to absorb radiation of a particular frequency from the cosmic microwave background – the afterglow of the Big Bang.
A timeline of the universe, updated to show when the first stars emerged. This updated timeline of the universe reflects the recent discovery that the first stars emerged by 180 million years after the Big Bang. Credit: N.R.Fuller, National Science Foundation
In the intervening billions of years the universe has expanded, stretching the wavelength of this absorbed radiation, meaning the absorbed radiation is now a very different, lower, frequency to what it was when it was first absorbed.
However, this absorbed radiation has left a signature in the radio spectrum of the cosmic microwave background, which can be detected even today.
The complication is that, because of the stretching of the wavelength, this frequency couldn’t be precisely calculated, meaning the researchers had to search through all the radiowaves surrounding Earth looking for the exact signature left behind.
The radio signal the US team found was incredibly faint, coming from 13.6 billion years back in the universe’s history. It also fell in the region of the spectrum used by FM radio stations, making detection of this weak signal from most Earth-based sites impossible.
What allowed them to detect this signal was Australia’s unique Murchison Radio-astronomy Observatory – an area in remote Western Australia where radio transmissions are banned by law.
This makes Murchison an almost perfect radio-quiet zone, where rather than picking up transmissions of the latest Vance Joy single on Triple J, the astronomers knew that their equipment would detect only signals coming from the universe
Even then, they needed to spot the signal through the cacophony of the rest of the universe, some 10,000 times louder than the signal they were searching for. Essentially, it was like trying to pick out your favourite song playing faintly in the background while listening to every radio station at once.
Rethinking the nature of dark matter
Artist’s rendering of how the first stars in the universe may have looked. Credit: N.R.Fuller, National Science Foundation
One of the observations from the study also suggested some new perspectives on dark matter – the mysterious matter that is so far undetectable, but causes effects which can be observed throughout the universe.
The gas cloud being excited by the first rays of light was extremely cold, with the signal revealing it was around twice as cold as we previously thought.
A separate group of researchers suggest that this means the gas was cooled through the interaction of hydrogen with something that is even colder — dark matter.
It’s this cooling of the cloud that has astronomers, like Professor Alan Duffy excited.
“This is a giant cloud of gas, unexpectedly cold and efficiently blocking that signal. The early Universe was a simple time, as quite literally there had not been much time for things to form that would complicate the picture. Most objects, from stars to black holes, that might exist would tend to heat the gas.
“Not many things can cool the gas. The only thing possibly colder than this gas? Dark Matter.”
According to Duffy, this finding has the potential to add to our understanding of dark matter’s very nature.
“The dark matter is a ghost, able to travel through solids, much less a gas, without ever colliding. Yet if the dark matter somehow collided with gas in the early universe then it would leach the energy from it and cool it just as seen by this experiment.”
“This is potentially one of the greatest clues as to the nature of dark matter.”
“This would be the first glimpse into the dark matter interacting with atoms with some different kind of force,” Duffy said.
On the basis of the signal measured in Western Australia, the researchers argue that the dark-matter particle could be no heavier than the mass of several protons.
Unlocking the deep past for the future
The signals detected have not only given us an insight into the early universe and the factors in play at the cosmic dawn, they have given us a refined timeline as to when the universe’s dark ages finished and stars began to form following the Big Bang.
The findings will also allow researchers to be able to further map the early universe in detail by searching for variations in the signal. Discovering the signal and the frequency at which is occurs will allow astronomers to home-in on the signal and measure it in ever finer detail using telescopes that make up the square kilometre array.
From that close-detailed scrutiny, we may find even more secrets of the universe, and understand more about how matter, and eventually us, came into existence.
The research has been published in Nature – Signals from earliest stars, and possible interactions with dark matter
Video courtesy of the National Science Foundation
