The researchers, led by the University of Cambridge, have developed a method that allows them to observe and study the first stars through the hydrogen clouds that filled the Universe some 378,000 years after the Big Bang.
Observe the birth of the first person stars and galaxies has been the goal of astronomers for decades, as it will help explain how the Universe evolved from the void after the Big Bang to the complex realm of celestial bodies we observe today, 13.8 billion years later.
The Square Kilometer Array (SKA) – a next-generation telescope to be completed by the end of the decade – will likely produce the earliest images of light in the Universe. However, for current telescopes, the challenge is to detect the cosmic signals of stars through thick clouds of hydrogen.
The signal that astronomers aim to detect is expected to be about a hundred thousand times weaker than other radio signals from the sky – for example, radio signals originating from our own galaxy. we.
The use of radio telescopes will distort the received signal, which could completely obscure the cosmic signal of interest. This is considered a severe observational challenge in modern radio cosmology. Such tool-related distortions are often thought to be the main bottleneck in this type of observation.
The Cambridge-led research team has now developed a methodology to see through primordial clouds and other sky noise signals, avoiding the adverse effects of distortion introduced by radio telescopes. . Their methodology, part of the REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) experiment, will allow astronomers to observe the earliest stars through their interactions with clouds. hydrogen, the same way we infer landscapes by looking at the shadows in the fog.
Their method will improve the quality and reliability of radio telescope observations of this unexplored pivotal moment in the evolution of the Universe. The first observations from REACH are expected later this year.
The result is report in the magazine Natural Astronomy.
Dr Eloy de Lera Acedo from Cambridge’s Cavendish Laboratory, lead author of the paper, said: “At the time the first stars formed, the Universe was mostly empty and consisted mainly of hydrogen and helium.
He added: “Due to gravity, the elements eventually came together and the conditions were right for nuclear fusion, which is what formed the first stars. But they are surrounded by clouds called neutral hydrogen, which absorb light very well, so it is difficult to detect or directly observe the light behind the clouds.”
In 2018, another research group (running the ‘Global Re-ionization Era Signature Detection Experiment’ – or EDGES) published a result that suggested the earliest possible light detection. this, but astronomers were unable to repeat the results – leading them to believe that the initial results could be due to interference with the telescope being used.
“Initial results will require new physics to explain it, since the temperature of the hydrogen gas will be much cooler than our current understanding of the Universe. In addition, the unexplained higher temperature of the background radiation – often assumed to be the well-known Cosmic Microwave Background – may be the cause,” said de Lera Acedo.
He added: “If we can confirm that the signal found in the previous experiment is indeed from the first stars, the impact would be huge.”
To study this period in the evolution of the Universe, commonly known as the Cosmic Dawn, astronomers study the 21-centimeter line – a signature of hydrogen electromagnetic radiation in the early Universe. They looked for a radio signal that measured the contrast between the radiation from the hydrogen and the radiation behind the hydrogen fog.
The method developed by de Lera Acedo and his colleagues uses Bayesian statistics to detect cosmic signals in the presence of interference from the telescope and general noise from the sky, so that the signals can be isolated. .
To do this, modern techniques and technologies from different fields are required.
The researchers used simulations to mimic a real observation using multiple antennas, which improves the reliability of the data – previous observations relied on only a single antenna.
“Our method jointly analyzes data from multiple antennas and over a wider frequency range than comparable current devices. This approach will give us the information we need to analyze our Bayesian data,” said de Lera Acedo.
He added: “In essence, we forgot about traditional design strategies and focused instead on designing a telescope that fits how we intend to analyze the data – something like as an inverse design. This could help us measure everything from the Cosmic Dawn and into the re-ionization era, when the hydrogen in the Universe was re-ionized.”
Construction of the telescope is currently being completed at the Karoo radio reserve in South Africa, a site chosen for its excellent conditions for radio observations of the sky. It is far away from man-made radio frequency interference, for example TV and FM radio signals.
The REACH team consists of more than 30 multidisciplinary and worldwide researchers, with experts in areas such as theoretical and observational cosmology, antenna design, radio frequency devices, modeling digital imaging, digital processing, big data, and Bayesian statistics. REACH is co-led by Stellenbosch University in South Africa.
Professor de Villiers, co-lead of the project at Stellenbosch University in South Africa, said: “Although the antenna technology used for this device is quite simple, the deployment environments are harsh and remote, as well. As strict tolerances are required during the manufacturing process, making this a very challenging project to undertake. “
He added: “We’re excited to see how well the system will perform and are absolutely confident we’ll make that elusive detection.”
The Big Bang and very early times of the Universe are well understood epochs, thanks to the Cosmic Microwave Background (CMB) radiation studies. The late and widespread evolution of stars and other celestial bodies is even better understood. But the timing of the first light in the Universe is a fundamental piece of the puzzle missing in the history of the Universe.
Source: University of Cambridge
