July 21 () –
A team of astronomers has developed a method that will allow them to “see” through the fog of the early Universe and detect the light of the first stars and galaxies, as published in the journal ‘Nature Astronomy’.
The researchers, led by the University of Cambridge (United Kingdom), have developed a methodology that will allow them to observe and study the first stars through the hydrogen clouds 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 evolved from the post-Big Bang void to the complex realm of celestial objects we observe today, 13.8 billion years ago. after.
The Square Kilometer Array (SKA)–a next-generation telescope to be completed by the end of the decade–will probably be able to image the earliest light in the Universe, but for current telescopes the challenge is to detect the cosmological signature of the stars through the thick clouds of hydrogen.
The signal that astronomers are trying to detect is expected to be about 100,000 times weaker than other radio signals also coming from the sky, for example radio signals originating in our own galaxy.
The use of a radio telescope itself introduces distortions in the received signal, which can completely obscure the cosmological signal of interest. This is considered an extreme observational challenge in modern radiocosmology. These instrument-related distortions are often blamed as the main bottleneck in this type of observation.
Now, the Cambridge-led team has developed a methodology to see through primordial clouds and other noise signals from the sky, avoiding the detrimental effect of distortions introduced by the radio telescope. Its methodology, which is part of the REACH experiment (Radio Experiment for the Analysis of Cosmic Hydrogen), will allow astronomers to observe the first stars through their interaction with hydrogen clouds, in the same way that we would deduce a landscape by looking at the shadows in the mist.
Their method will improve the quality and reliability of observations from radio telescopes studying this key and uncharted epoch in the development of the Universe. The first REACH observations are expected by the end of this year.
“At the time the first stars formed, the Universe was mostly empty and made up mostly of hydrogen and helium. –explains the doctor Eloy de Lera Acedo, of the Cambridge Cavendish Laboratory, main author of the article–. Due to gravity, the elements ended up coming together and the conditions for nuclear fusion were created, which is what formed the first stars. But they were surrounded by clouds of so-called neutral hydrogen, which absorb light very well, so it’s hard to detect or observe light behind the clouds directly.”
In 2018, another research group, leading the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), published a result that hinted at a possible detection of this earlier light, but astronomers they have not been able to repeat the result – leading them to believe that the original result may have been due to interference from the telescope that was being used.
“The The original result would require new physics to explain it, due to the temperature of hydrogen gas, which should be much colder than our current understanding of the Universe allows. Alternatively, an unexplained higher temperature of the background radiation – which is normally assumed to be the well-known Cosmic Microwave Background – could be the cause, says de Lera Acedo. If we can confirm that the signal found in that earlier experiment really did come from the first stars, the implications would be huge.”
To study this period in the development of the Universe, often called the Cosmic Dawn, astronomers study the 21-centimeter line, a signature of electromagnetic radiation from hydrogen in the early Universe. They look for a radio signal that measures the contrast between the radiation from the hydrogen and the radiation 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 telescope interference and general sky noise, so that the signals can be separated. For this, cutting-edge techniques and technologies from different fields have been needed.
The researchers used simulations to mimic a real observation with multiple antennas, which improves the reliability of the data (previous observations were based on a single antenna).
“Our method jointly analyzes data from multiple antennas and over a wider frequency band than current equivalent instruments. This approach will provide us with the necessary information for our Bayesian analysis of the data,” explains de Lera Acedo. we forgot about traditional design strategies and focused on designing a telescope tailored to the way we plan to analyze the data, something like a reverse design. This could help us measure things from the Cosmic Dawn to the epoch of reionization , when the hydrogen in the Universe was reionized”.
The construction of the telescope is being finalized in the Karoo radio reserve, in South Africa, a place chosen for its excellent conditions for observing the sky by radio. It is far away from man-made radio frequency interference, for example TV and FM radio signals.
The REACH team, made up of more than 30 researchers, is multidisciplinary and distributed around the world, with experts in fields such as theoretical and observational cosmology, antenna design, radio frequency instrumentation, numerical modelling, digital processing , big data and Bayesian statistics. REACH is co-led by the University of Stellenbosch, in South Africa.
Professor de Villiers, co-director of the project at the University of Stellenbosch (South Africa), notes that, “Although the antenna technology used for this instrument is fairly straightforward, the harsh and remote deployment environment and the tight tolerances required in manufacturing make this a very difficult project to work on.“.
The Big Bang and the early days of the Universe are well-known epochs, thanks to studies of the Cosmic Microwave Background (CMB) radiation. The late and widespread evolution of stars and other celestial objects is still better understood. But the epoch of the formation of the first light of the Cosmos is a fundamental missing piece in the puzzle of the history of the Universe.