Studying the first stars through the mists of the early universe

Observing the birth of the first stars and galaxies has been the goal of astronomers for decades. This will explain the evolution of the universe.

The Cambridge University team has created a technique that allows them to see and study the first stars through the hydrogen cloud that covered the universe some 378,000 years after the Big Bang. Their methodology, part of the REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) experiment, will improve the quality and reliability of observations from radio telescopes that see this important new time in the Universe’s development.

Dr. Eloy de Lera Acedo of Cambridge Cavendish Laboratory, lead author of the paper, said, “By the time the first stars formed, the Universe was largely empty and made up mostly of hydrogen and helium. Due to gravity, the elements eventually came together due to gravity, and the conditions were just right for nuclear fusion, which formed the first stars. But they are surrounded by a cloud called neutral hydrogen, which absorbs light well, making it difficult to detect or observe the light behind the cloud directly.”

“The actual results would require new physics to explain because of the temperature of hydrogen gas, which should be much colder than our current understanding of the Universe. Alternatively, an unexplained higher temperature of the background radiation – usually thought of as the infamous Cosmic Microwave Background – could be to blame.

“The implications would be enormous if we could confirm that the signals found in previous experiments came from the first star.”

Astronomers probe the 21-centimeter line, a sign of electromagnetic radiation from hydrogen in the early universe, to examine this stage of the universe’s evolution, often referred to as the Cosmic Dawn. They looked for radio signals that compared the radiation from the hydrogen to the radiation behind the hydrogen fog.

The technique created by the scientists uses Bayesian statistics to identify cosmological signals in the presence of telescope interference and general sky noise, allowing the signals to be distinguished. To do this, cutting-edge techniques and technologies from various fields are required.

They used simulations to mimic real observations using multiple antennas, which increased the reliability of the data – previous observations relied on a single antenna.

de Lera Acedo says, “Our method jointly analyzes data from multiple antennas and across a wider frequency band than equivalent current instruments. This approach will provide us with the information needed for our Bayesian data analysis.”

“Essentially, we forgo the traditional design strategy and focus instead on designing a telescope that fits the way we plan to analyze the data – something like an inverted design. This could help us measure things from Cosmic Dawn and to the reionization age when hydrogen in the universe was reionized.”

Construction of the telescope is currently being completed at the Karoo radio reserve in South Africa, a location chosen because of its excellent conditions for radio observations in the sky. Away from man-made radio frequency interference, such as television and FM radio signals.

Professor de Villiers, one of the project leaders at Stellenbosch University in South Africa, said: “Although the antenna technology used for this instrument is rather simple, the harsh deployment environment and long distances, and the tight tolerances required in its manufacture, made this a very challenging project to work on.”

He added: “We are excited to see how well the system performs and have full confidence that we will make the elusive detection.”

Journal Reference:

1. E. de Lera Acedo et al.: ‘REACH radiometer for detecting hydrogen signal 21 cm from redshift z 7.5–28.’ Natural Astronomy (July 2022). DOI: 10.1038/s41550-022-01709-9

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