Oldest stars in the universe may be revealed with new technique

Artist's impression of the emergence of stars in the early Universe.
First stars emerged from thick hydrogen clouds in the young universe about 400,000 years after the Big Bang. (Image credit: NASA/ JPL-Caltech)

Astronomers think that a new observation technique relying on the detection of faint radio signals will allow them to see the first stars that formed in the middle of thick hydrogen clouds shortly after the birth of the universe. 

The technique, introduced in a new paper, looks for a type of electromagnetic radiation signature known as the 21-centimeter line, which was emitted by hydrogen atoms that filled the young universe in the first hundreds of thousands of years after the Big Bang

The signal is extremely weak, about a hundred thousand times weaker than radio signals emitted by objects in our galaxy, the Milky Way. To separate the signal from all the other noise detected by the radio antennas will require a complex data analysis. 

"Our method jointly analyzes data from multiple antennas and across a wider frequency band than equivalent current instruments," Eloy de Lera Acedo, an astronomer at Cambridge University in the U.K. and lead author of the new paper said in a statement.

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By measuring the contrast between the radiation from the hydrogen clouds and the signal behind them, the astronomers hope to 'see' the stars as if they were "shadows in the fog."

"At the time when the first stars formed, the universe was mostly empty and composed mostly of hydrogen and helium," de Lera Acedo said in the statement. "Because of gravity, the elements eventually came together and the conditions were right for nuclear fusion, which is what formed the first stars. But 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."

The James Webb Space Telescope, which has recently released its first science-grade images, also looks for the first light in the universe, but using a different technique. Webb detects infrared radiation, which is essentially heat. Since heat can penetrate dust clouds, Webb, too, enables astronomers to peer into the universe's most impenetrable regions.

The new radio astronomy method was developed as part of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) project and builds on earlier observations that hinted at the detection of the 21-centimeter line. Those earlier measurements, however, couldn't be replicated, which led scientists to believe that the signal may have been an error. 

"If we can confirm that the signal found in that earlier experiment really was from the first stars, the implications would be huge," de Lera Acedo said.

The researchers used simulations mimicking real observations using multiple radio antennas, which improved the reliability of the data compared to the earlier measurements relying on a single antenna.

The new measurements will be conducted later this year in Karoo in South Africa. 

"We are extremely excited to see how well the system will perform, and have full confidence we'll make that elusive detection," Dirk de Villiers, a radio astronomer at the University of Stellenbosch in South Africa and co-lead author of the new paper, said in the statement.

Scientists previously detected signals from the Big Bang in the form of the cosmic microwave background, but the emergence of the first stars in the universe after the dark ages of its early hundreds of thousands of years is still a missing piece. 

The paper was published in the journal Nature Astronomy on Thursday (July 21).

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Tereza Pultarova
Senior Writer

Tereza is a London-based science and technology journalist, aspiring fiction writer and amateur gymnast. Originally from Prague, the Czech Republic, she spent the first seven years of her career working as a reporter, script-writer and presenter for various TV programmes of the Czech Public Service Television. She later took a career break to pursue further education and added a Master's in Science from the International Space University, France, to her Bachelor's in Journalism and Master's in Cultural Anthropology from Prague's Charles University. She worked as a reporter at the Engineering and Technology magazine, freelanced for a range of publications including Live Science, Space.com, Professional Engineering, Via Satellite and Space News and served as a maternity cover science editor at the European Space Agency.