WE COULD SOON PEER THROUGH TIME TO SEE THE FIRST STARS
By analysing primordial clouds of hydrogen, astronomers could detect traces of light from the earliest stars and galaxies
Observing the birth of the first stars and galaxies has been a sought-after goal of astronomers for decades. And now a worldwide team has developed a way to observe these ancient stars by looking through the clouds of fog that filled the Universe around 378,000 years after the Big Bang.
The research, part of the REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) experiment, will allow astronomers to observe the earliest stars by studying these primordial hydrogen clouds with a radio telescope.
“At the formation of the first stars, the Universe was mostly empty and composed mostly of hydrogen and helium. Because of gravity, these elements eventually came together and the conditions were right for nuclear fusion, which is what formed the first stars,” said lead researcher Dr Eloy de Lera Acedo, from Cambridge’s Cavendish Laboratory. “They were surrounded by clouds of so-called neutral hydrogen, which absorb light really well, so it’s hard to detect or observe the light behind the clouds directly.”
To study the cosmic dawn, they are looking at the 21-centimetre line – a characteristic signal of the presence of hydrogen. It’s always the same at the source, which means it’s a recognisable signal to look for in your radio telescope data. Therefore, when you point the telescope in a certain direction, you can use this line to distinguish older, more distant hydrogen from the younger, closer stuff. The signal can also tell us about the stars hiding behind the hydrogen, since the light from these stars heats and ionises the hydrogen clouds, which in turn affects this signal. Therefore, by looking at the radio signal from hydrogen, we can tell a lot about these first stars. They have carried out simulations using multiple antennas to mimic a real observation – when earlier observations have relied on one antenna – to improve the reliability of the data.
“We forgot about traditional design strategies and instead focused on designing a telescope suited to the way we plan to analyse the data – something like an inverse design,” said de Lera Acedo. “This could help us measure things from the cosmic dawn and into the epoch of reionisation, when hydrogen in the Universe was reionised.”
The team has had to overcome issues, such as distortions being introduced to the signal received. Plus, the elusive signal the team is searching for is expected to be around 100,000 times weaker than other radio signals coming from the sky, such as those from our Galaxy.
With the research method in place, the first observations from the REACH telescope are expected later this year.