The infantile universe was hot, rather than cold, before it lights up, say astronomers
Using the Widefield Array Murchison telescope (MWA) at the CSIRO Murchisono-Astronomical Observatory, astronomers are looking for the elusive era of reionization, a period at the beginning of the history of the universe which is predicted by theory but but to detect using radiotelescopes; It means the end of the dark cosmic ages, about a billion years after the Big Bang, when the gas between the galaxies went from the opaque to transparent, allowing the light of the first stars and galaxies to travel throughout the universe.
A small part of the sky seen in the radio waves by the Widefield Murchison table. Image credit: Nunhokee and al. / ICRAR / CURTIN University.
“Our research has been carried out on two phases,” said Dr. Ridhima Nunhokee, astronomer of the node of Curtin University at the International Research Center on Radio-Astronomy (ICRAR) and the Center of Excellence of the Arc for the entire 3-dimensional Sky Astrophysics (Astro 3D).
“During the initial research, we obtained our first heating proofs from the intergalactic environment, the gas between galaxies, 800 million years after the Big Bang.”
“To study this first period of the universe, we must isolate the weak signal of the time of reionization, identify and remove all other sources of radio waves in the universe of their observations.”
“These include emissions from neighboring stars and galaxies, interference from the earth’s atmosphere, and even the noise generated by the telescope itself.”
“It is only after having carefully subtracting these” leading signals “that the remaining data reveal signals from the time of re -seening.”
“From this research, we have developed methods to deal with the contamination of the foreground, and subtract the signals that we do not want, but also better understand our telescope and propose a clean signal.”
“We were also able to join about ten years of MWA data together, to observe the sky for longer than ever before.”
“This is the other reason why we got closer to detecting the signal.”
According to the team, the quality and the quantity of this new set of data are what made this discovery possible.
A cold universe would produce a signal that would have been visible in the new data.
The absence of this signal excludes such a “cold start” to reionization and means that the universe must have been “preheated” before re -recovery.
“As the universe evolves, gas between the galaxies is expanded and cools, we therefore expect it to be very, very cold,” said Professor Cathryn Trott, astronomer of the node of Curtin university in Icrar, Astro 3D and the Curtin Institute of Radio Astronomy.
“Our measures show that it is at least heated by a certain quantity. Not much, but that tells us that very cold reionization is excluded. It is really interesting.”
“Research suggests that this heating is probably driven by energy from early sources of X -ray from early black holes and stellar remains spreading into the universe.”
The results appear in two articles in the Astrophysical Journal.
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CD Nunhokee and al. 2025. Limits on the power spectrum from 21 cm to Z = 6.5–7.0 Observations in the Widefield moodison table. APJ 989, 57; Two: 10.3847 / 1538-4357 / Adda45
Cathryn M. Trott and al. 2025. Improvement of the signal limits from 21 cm to Z = 6.5–7.0 with the Widefield Murchison table using Gaussian information. APJ 991, 211; Two: 10.3847 / 1538-4357 / ADFF80
