A group of astronomers has created a technique that will enable them to “see” through the early Universe’s haze and find the light coming from the universe’s earliest stars and galaxies.

The team of scientists, headed by the University of Cambridge, 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.

Astronomers have long sought to watch the formation of the first stars and galaxies as it will help them understand how the Universe changed from the empty space following the Big Bang to the intricate universe of celestial objects we see today, 13.8 billion years later.

The Square Kilometre Array (SKA), a next-generation telescope scheduled for completion by the end of the decade, will probably be able to capture images of the Universe’s earliest light, but for existing telescopes, the challenge is to find the stars’ cosmological signals through the dense hydrogen clouds.

The signal that astronomers hope to find is anticipated to be around 100,000 times weaker than other radio signals that are also coming from the sky, such as radio signals coming from within our own galaxy.

The use of a radio telescope imparts distortions to the received signal, which can entirely hide the cosmological signal of interest. In contemporary radio cosmology, this is regarded as an extremely difficult observational challenge. Such instrument-related distortions are frequently held responsible for being the main obstacle in this kind of observation.

The Cambridge-led team has now created a mechanism to look through the primordial clouds and other sky noise signals, eliminating the negative impact of the radio telescope’s distortions. With the help of their technique, which is a component of the REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) experiment, astronomers will be able to observe the first stars by way of their interactions with the hydrogen clouds, much like how we can infer a landscape from the shadows in the fog.

Their approach will raise the standard and dependability of observations made by radio telescopes during this crucial yet unknown period in the Universe’s evolution. Later this year, the first REACH observations are anticipated.

The findings were published today in the journal Nature Astronomy.

According to the lead author of the study Dr. Eloy de Lera Acedo of Cambridge’s Cavendish Laboratory, “the Universe was mostly empty and composed mostly of hydrogen and helium at the time the first stars formed.”

Gravitation eventually brought the elements together and created the ideal conditions for nuclear fusion, which is what created the first stars,” according to him. However, they were encircled by clouds of ‘neutral hydrogen,’ which are excellent light absorbers, making it difficult to immediately detect or monitor the light behind the clouds.

Astronomers have been unable to replicate the original result, which has led them to believe that the original result may have been caused by interference from the telescope being used. In 2018, another research group (running the “Experiment to Detect the Global Epoch of Reioniozation Signature,” or EDGES) published a study that hinted at a possible detection of this earliest light.

The temperature of the hydrogen gas should be substantially cooler than what our existing understanding of the Universe would allow, therefore the original conclusion would require new physics to explain it. Alternately, the cause could be an unexplained increase in the background radiation’s temperature, which is commonly thought to be the well-known Cosmic Microwave Background, according to de Lera Acedo.

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

Astronomers use the 21-centimeter line, an electromagnetic radiation signature from hydrogen in the early Universe, to study this period of the Universe’s development, known as the Cosmic Dawn. They search for a radio signal that compares the radiation coming from the hydrogen to the radiation coming from behind the hydrogen fog.

The technique created by de Lera Acedo and his associates makes use of 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, they had to use cutting-edge methods and tools from many different fields.

Earlier observations depended on a single antenna, thus the simulations the researchers performed to recreate an actual observation using many antennas improved the data’s trustworthiness.

“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,” adds de Lera Acedo.

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

The final steps of building the telescope are being done at the Karoo radio reserve in South Africa, which was chosen because it is a great place for radio observations of the sky. It’s far from TV and FM radio waves created by humans.

REACH’s multidisciplinary and global team of approximately 30 researchers includes specialists in theoretical and observational cosmology, antenna design, radio frequency instrumentation, numerical modeling, digital processing, big data, and Bayesian statistics. REACH is co-led by Stellenbosch University in South Africa.

At the South African University of Stellenbosch, Professor de Villiers, who is also the project’s co-leader, adds: “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.”

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

Studies of the Cosmic Microwave Background (CMB) radiation have made it possible to have a better understanding of the universe’s early history. Even better understood is how stars and other objects in space changed slowly and over a large area. But the timing of the formation of the first light in the universe is a crucial missing element in the history of the cosmos.

Image Credit: NASA/ JPL-Caltech

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