Studying the first stars through the fog of the early Universe

Observing the birth of the first stars and galaxies has been a goal of astronomers for decades. It will explain the evolution of the Universe.

The University of Cambridge‘s team has created a technique that will enable them to see and study the first stars through the hydrogen clouds 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 looking at this new key time in the development of the Universe.

Dr. Eloy de Lera Acedo from Cambridge’s Cavendish Laboratory, the paper’s lead author, said, “At the time when the first stars formed, the Universe was mostly empty and composed mostly of hydrogen and helium. Because of gravity, the elements eventually came together because of gravity, and the conditions were right for nuclear fusion, which formed the first stars. But they were surrounded by clouds of so-called neutral hydrogen, which absorb light well, so it’s hard to detect or observe the light behind the clouds directly.”

“The actual result would require new physics to explain it due to the temperature of the hydrogen gas, which should be much cooler than our current understanding of the Universe would allow. Alternatively, an unexplained higher temperature of the background radiation – typically assumed to be the well-known Cosmic Microwave Background – could be the cause.”

“The implications would be huge if we can confirm that the signal found in that earlier experiment was from the first stars.”

Astronomers investigate the 21-centimeter line, an electromagnetic radiation signature from hydrogen in the early Universe, to research this stage of the Universe’s evolution, which is frequently referred to as the Cosmic Dawn. They search for a radio signal that compares the radiation from the hydrogen to the radiation behind the hydrogen fog.

The technique created by scientists uses Bayesian statistics to identify a cosmological signal in the presence of telescope interference and general sky noise, allowing the signals to be distinguished. To do this, state-of-the-art techniques and technologies from different fields have been required.

They used simulations to mimic a real observation using multiple antennas, which improves the reliability of the data – earlier observations have relied on a single antenna.

de Lera Acedo said, “Our method jointly analyses data from multiple antennas and across a wider frequency band than equivalent current instruments. This approach will give us the necessary information for our Bayesian data analysis.”

“In essence, we forgot about traditional design strategies and instead focused on designing a telescope suited to the way we plan to analyze the data – something like an inverse design. This could help us measure things from the Cosmic Dawn and into the epoch of reionization when hydrogen in the Universe was reionized.”

The telescope’s construction is currently being finalized at the Karoo radio reserve in South Africa, a location chosen for its excellent conditions for radio observations of the sky. It is far from human-made radio frequency interference, such as television and FM radio signals.

Professor de Villiers, co-lead of the project at the University of Stellenbosch in South Africa, said: “Although the antenna technology used for this instrument is rather simple, the harsh and remote deployment environment, and the strict tolerances required in the manufacturing, make this a very challenging project to work on.”

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

Journal Reference:

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