The failure to detect the key signal allows astronomers to determine what the first galaxies were and were not, as

The failure to detect the key signal allows astronomers to determine what the first galaxies were and were not, as


Credit: Pixabay/CC0 Public domain

Researchers were able to make key determinations about the first galaxies to exist, in one of the first astrophysical studies of the period in the early universe when the first stars and galaxies formed, known as the cosmic dawn.

Using data from India’s SARAS3 radio telescope, researchers led by the University of Cambridge were able to observe the very first universe, just 200 million years after the Big Bang, and set limits on the mass production and of energy from the first stars and galaxies.

Unexpectedly, the researchers were able to place these boundaries on early galaxies by not finding the signal they were looking for, known as the 21-centimeter hydrogen line.

This non-detection allowed researchers to make further determinations about the cosmic dawn, placing constraints on early galaxies, allowing them to rule out scenarios that included galaxies that were inefficient cosmic gas heaters and producers. effective radio broadcasts.

Although we cannot yet directly observe these first galaxies, the results, reported in the journal natural astronomyrepresent an important step in understanding how our universe went from almost empty to full of stars.

Understanding the early universe, when the first stars and galaxies formed, is one of the major goals of the new observatories. The results obtained from the SARAS3 data constitute a proof-of-concept study that opens the way to understanding this period in the development of the universe.

The SKA project, involving two next-generation telescopes to be completed by the end of the decade, will likely be able to image the early universe, but for current telescopes the challenge is to detect the signal cosmology of the first stars re-radiated by thick clouds of hydrogen.

The failure to detect the key signal allows astronomers to determine what the first galaxies were and were not, as

The origin of the 21 cm radio emission line: the transition from parallel spin to opposite spin in a neutral hydrogen atom. Credit: Hellingspaul/Wikimedia Commons, CC BY-SA

This signal is known as the 21 centimeter line, a radio signal produced by hydrogen atoms in the early universe. Unlike the recently launched JWST, which will be able to directly image individual galaxies in the early universe, studies of the 21 centimeter line, carried out with radio telescopes such as the Cambridge-led REACH (Radio Experiment for the Analysis of Cosmic Hydrogen), can tell us about entire populations of even older galaxies. The first results of REACH are expected in early 2023.

To detect the 21-centimeter line, astronomers are looking for a radio signal produced by hydrogen atoms in the early universe, affected by light from early stars and radiation behind hydrogen fog. Earlier this year, the same researchers developed a method they say will allow them to see through the fog of the early universe and detect the light of the first stars. Some of these techniques have already been put into practice in this study.

In 2018, another research group exploiting the EDGES experiment published a result suggesting a possible detection of this first light. The reported signal was exceptionally strong compared to what is expected in the simplest astrophysical image of the early universe. Recently, SARAS3 data challenged this detection: the EDGES result still awaits confirmation from independent observations.

In a new analysis of SARAS3 data, the Cambridge-led team tested a variety of astrophysical scenarios that could potentially explain the EDGES result, but they found no corresponding signal. Instead, the team was able to put some limits on the properties of early stars and galaxies.

The results of the SARAS3 analysis are the first time that radio observations of the 21-centimeter mean line have been able to provide insight into the properties of early galaxies in the form of boundaries of their major physical properties.

Working with collaborators in India, Australia and Israel, the Cambridge team used data from the SARAS3 experiment to search for signals from cosmic dawn, when the first galaxies formed. Using statistical modeling techniques, the researchers were unable to find a signal in the SARAS3 data.

“We were looking for a signal with a certain amplitude,” said Harry Bevins, a Ph.D. student at Cambridge’s Cavendish Laboratory and lead author of the paper. “But by not finding this signal, we can limit its depth. This, in turn, begins to tell us about the brightness of early galaxies.”

“Our analysis showed that the hydrogen signal can tell us about the population of early stars and galaxies,” said co-lead author Dr Anastasia Fialkov of the Cambridge Institute of Astronomy. “Our analysis places bounds on some of the key properties of early light sources, including the masses of early galaxies and the efficiency with which these galaxies can form stars. We also address the question of how efficiently these sources emit X-rays, radio and ultraviolet radiation.

“This is a first step for us in what we hope will be a decade of discoveries about how the universe evolved from darkness and emptiness to the complex realm of stars, galaxies and other celestial objects that we can see from Earth today,” said Dr. Eloy de Lera Acedo of Cambridge’s Cavendish Laboratory, who co-led the research.

The observational study, the first of its kind in many ways, rules out scenarios in which early galaxies were both more than a thousand times brighter than current galaxies in their radio emission and were poor heaters of hydrogen gas.

“Our data also reveals something that has been suggested before, that early stars and galaxies may have had a measurable contribution to the background radiation that appeared in the aftermath of the Big Bang and has been heading our way ever since,” said de Lera Acedo, “We also set a limit to this contribution.”

β€œIt’s amazing to be able to look so far back in time – just 200 million years after the Big Bang – and be able to learn more about the early universe,” Bevins said.

More information:
Harry Bevins, Astrophysical Constraints of SARAS 3’s Non-Detection of the 21cm Signal Averaged by the Cosmic Dawn Sky, natural astronomy (2022). DOI: 10.1038/s41550-022-01825-6.

Provided by the University of Cambridge

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