A group of astronomers have developed a method that will allow them to “see” through the fog of the early universe and detect light from the first stars and galaxies.
Researchers led by the University of Cambridge have developed a methodology that will allow them to observe and study the first stars through clouds of hydrogen that filled the universe about 378,000 years after the Big Bang.
Observing the birth of the first stars and galaxies has been a goal of astronomers for decades, as it will help explain how the universe went from a void after the Big Bang to the complex realm of celestial objects we observe today, 13.8 billion years later.
The Square Kilometer Array (SKA) — a next-generation telescope due to be completed by the end of the decade — will likely be able to image the earliest light in the universe, but for current telescopes, the challenge is to detect the cosmological signal of stars through thick hydrogen clouds.
The signal that astronomers are looking for is expected to be about a hundred thousand times weaker than other radio signals that also come from the sky, such as radio signals from our own galaxy.
The use of the radio telescope itself introduces distortions into the received signal, which can completely hide the cosmological signal of interest. This is considered an extremely difficult task in modern radio cosmology. Such instrument-related distortions are commonly referred to as the main bottleneck in this type of observation.
Now, a Cambridge-led team has developed a methodology to see through primordial clouds and other noisy sky signals while avoiding the detrimental effect of radio telescope distortion. Their methodology, which is part of the REACH (Radio Space Hydrogen Analysis) experiment, will allow astronomers to observe the earliest stars through their interactions with hydrogen clouds, just as we infer landscape by looking at shadows in space. fog.
Their method will improve the quality and reliability of observations from radio telescopes by looking at this unexplored pivotal moment in the evolution of the universe. The first REACH sightings are expected later this year.
The results are published today in the journal Astronomy of nature.
“At the time the first stars formed, the universe was mostly empty and consisted mostly of hydrogen and helium,” said Dr. Eloy de Lera Acedo of the Cambridge Cavendish Laboratory, lead author of the paper.
He added: “Due to gravity, the elements eventually combined and the conditions were right for the nuclear fusion that formed the first stars. But they were surrounded by clouds of so-called neutral hydrogen, which absorb light very well, so it is difficult to detect or observe the light behind the clouds directly.”
In 2018, another research group (which conducted the “Global Reionization Epoch Signature Detection Experiment” – or EDGES) published a result hinting at the possible detection of this earliest light, but astronomers were unable to replicate the result, leading them to believe that the original result could be related to interference from the telescope being used.
“The initial result would require an explanation of new physics due to the temperature of hydrogen gas, which must be much lower than our current understanding of the universe allows. Alternatively, the inexplicably higher temperature of the background radiation—generally thought to be the well-known Cosmic Microwave Background—may be the cause,” de Lera Acedo said.
“If we can confirm that the signal found in this earlier experiment did indeed come from the first stars, the implications would be huge.”
To study this period in the evolution of the universe, often referred to as the Cosmic Dawn, astronomers study the 21-centimeter line, the electromagnetic signature of hydrogen in the early universe. They are looking for a radio signal that measures the contrast between the hydrogen emission and the emission behind the hydrogen fog.
The methodology developed by de Lera Acedo and colleagues uses Bayesian statistics to detect a cosmological signal in the presence of interference from a telescope and general noise from the sky so that the signals can be separated.
This required the most modern techniques and technologies from different fields.
The researchers used simulations to mimic a real-world observation using multiple antennas, which improves the reliability of the data – earlier observations relied on a single antenna.
“Our method jointly analyzes data from multiple antennas and over a wider frequency range than equivalent state-of-the-art instruments. This approach will give us the information we need for our Bayesian data analysis,” said de Lera Acedo.
“Essentially, we forgot about traditional design strategies and instead focused on developing a telescope that is suitable for how we plan to analyze the data – sort of like reverse design. This can help us measure things from the Cosmic Dawn to the age of reionization. when the hydrogen in the universe reionized.”
The telescope is currently being completed at the Karoo Radio Conservation Area 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 such as TV and FM radio signals.
The REACH team of more than 30 researchers is multidisciplinary and distributed around the world and includes experts in areas such as theoretical and observational cosmology, antenna design, radio frequency equipment, numerical modeling, digital processing, big data and Bayesian statistics. REACH is jointly led by Stellenbosch University in South Africa.
Professor de Villiers, co-leader of the project at Stellenbosch University in South Africa, said: “While the antenna technology used for this instrument is quite simple, the harsh and remote deployment conditions, as well as the tight manufacturing tolerances required, make it very difficult to project.”
“We are very excited to see how well the system will perform and have full confidence that we can make this elusive detection.”
The big bang and the very early periods of the universe are well understood through studies of the cosmic microwave background (CMB) radiation. Even better studied is the late and widespread evolution of stars and other celestial objects. But the timing of the formation of the first light in the Cosmos is a fundamental missing piece in the puzzle of the history of the Universe.
An ocean of galaxies awaits: new COMAP radio survey
Eloy de Lera Acedo, REACH radiometer for detection of 21 cm hydrogen signal with redshift z ≈ 7.5–28, Astronomy of nature (2022). DOI: 10.1038/s41550-022-01709-9. www.nature.com/articles/s41550-022-01709-9
Courtesy of the University of Cambridge
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