Astronomers are developing a new way to ‘see’ early stars through the haze of the early Universe

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A team of astronomers has 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.

The researchers, led by the University of Cambridge, have developed a methodology that will allow them to observe and study the first stars through the hydrogen clouds that filled the Universe around 378,000 years later. 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 vacuum after the Big Bang to the complex realm of celestial objects we observe today, 13.8 billions of 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 Universe’s first light, but for current telescopes the challenge is to detect the cosmological signal from the stars through the thick clouds of hydrogen.

The signal that astronomers aim to detect should be about a hundred thousand times weaker than other radio signals also coming from the sky – for example, radio signals coming from our own galaxy.

The use of a radio telescope itself introduces distortions into the received signal, which can completely obscure the cosmological signal of interest. This is considered an extreme observational challenge in modern radio cosmology. Such instrument-related distortions are often blamed for being the main bottleneck in this type of observation.

Now the Cambridge-led team has developed a methodology to see through primordial clouds and other sky noise signals, avoiding the detrimental effect of distortions introduced by the radio telescope. Their methodology, which is part of the REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) experiment, will allow astronomers to observe the first stars through their interaction with hydrogen clouds, the same way we do. deduce a landscape by looking at the shadows in the fog.

Their method will improve the quality and reliability of radio telescope observations at this key unexplored moment in the development of the Universe. The first observations of REACH are expected later this year.

The results are published today in the journal natural astronomy.

“At the time the first stars formed, the Universe was essentially empty and composed mainly of hydrogen and helium,” said Dr Eloy de Lera Acedo of the Cavendish Laboratory in Cambridge, lead author of the paper.

He added: “Because of gravity, the elements eventually came together and the conditions were set for nuclear fusion, which formed the first stars. But they were surrounded by so-called neutral hydrogen clouds, which absorb light very well, so it’s hard to detect or directly observe the light behind the clouds.”

In 2018, another research group (conducting the “Experiment to detect the global epoch of the reioniozation signature” – or EDGES) published a result that hinted at a possible detection of this first light, but astronomers didn’t were unable to repeat the result – leading them to believe that the original result may have been due to interference from the telescope used.

“The original result would require new physics to explain it, due to the temperature of hydrogen gas, which would have to be much colder than our current understanding of the Universe would allow. Alternatively, an unexplained higher temperature of the background radiation — generally assumed to be the well-known cosmic microwave background — could be the cause,” said de Lera Acedo.

He added: “If we can confirm that the signal found in this earlier experiment really came from early 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 – an electromagnetic radiation signature of hydrogen in the early Universe. They are looking for a radio signal that measures the contrast between the hydrogen radiation and the radiation behind the hydrogen mist.

The methodology developed by de Lera Acedo and his 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.

To do this, advanced techniques and technologies from different fields were needed.

The researchers used simulations to mimic a real observation using multiple antennas, which improves data reliability – previous observations relied on a single antenna.

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

He added: “In essence, we forgot about traditional design strategies and instead focused on designing a telescope that fits the way we plan to analyze the data – something like an inverted design. This could help us measure things from the cosmic dawn and into the epoch of reionization, when the hydrogen in the Universe was reionized.”

The construction of the telescope is currently being finalized in the Karoo radio reserve in South Africa, a location chosen for its excellent conditions for radio observation of the sky. It is far from man-made radio frequency interference, for example TV and FM radio signals.

The REACH team of over 30 researchers is multidisciplinary and globally distributed, with experts in areas such as theoretical and observational cosmology, antenna design, radio frequency instrumentation, numerical modeling, numerical processing , big data and Bayesian statistics. REACH is co-led by the University of Stellenbosch in South Africa.

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

He added: “We are extremely excited to see how well the system will perform and are fully confident that we will make this elusive detection.”

The Big Bang and the early days of the Universe are well-understood epochs, thanks to studies of cosmic microwave background (CMB) radiation. The late and widespread evolution of stars and other celestial objects is even better understood. 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.

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