Astronomers utilizing CSIRO’s Murchison Wide Field Array (MWA) telescope are on the quest to uncover the elusive period of reionization. This early stage in the universe’s history has been theorized but remains undetected by radio telescopes. This period marks the end of the universe’s dark ages, occurring approximately a billion years post-Big Bang, during which intergalactic gases transform from opaque to transparent, enabling light from the first stars and galaxies to permeate the cosmos.
A glimpse of the sky observed in radio waves by the Murchison Wide Field Array. Image credit: Nunhokee et al. / ICRAR / Curtin University.
“Our research was conducted in two phases,” stated Dr. Riddhima Nunhokey, an astronomer at Curtin University Node of the International Center for Radio Astronomical Research for All Sky Astrophysics (ICRAR).
“In the initial phase, we discovered the first signs of heating in the intergalactic gas—the intergalactic medium—around 800 million years after the Big Bang.”
“To examine this primordial phase of the universe, we must isolate faint signals from this epoch while eliminating all other sources of cosmic radio emissions.”
“These sources include emissions from nearby celestial bodies, interference from Earth’s atmosphere, and even noise generated by the telescope itself.”
“Only after meticulously subtracting these ‘foreground signals’ can we discern the signals from the era of reionization.”
“From this study, we have developed methods to manage foreground contamination and remove unwanted signals, thus enhancing our understanding of telescopes and improving the clarity of detected signals.”
“We are also able to integrate nearly a decade’s worth of MWA data, allowing us to make observations over a longer timeframe than before.”
“This is another reason we are closer than ever to detecting the signals.”
The team asserts that the enhanced quality and quantity of this new dataset made this discovery feasible.
The cold universe is producing signals that resemble these new data.
This absence of signals indicates that reionization must have commenced from a “cold start,” implying that the universe was “preheated” prior to the reionization phase.
“As the universe expands, intergalactic gases cool down, and thus we expect them to become extremely cold,” explained Professor Cathryn Trott, an astronomer at ICRAR’s Curtin University Node, associated with Astro 3D and the Curtin Institute of Radio Astronomy.
“Our measurements suggest that there is a certain level of heating present. While it may not be substantial, it does indicate that extremely cold reionization is unlikely, and that’s quite intriguing.”
“This study implies that this heating is probably influenced by energy from early black holes and primordial X-ray sources resulting from stellar remnants spread across the universe.”
The findings are presented in two papers in the Astrophysical Journal.
____
CD Nunhokee et al. 2025. The 21 cm power spectrum limit of z = 6.5–7.0 based on Murchison wide field array observations. APJ 989, 57; doi:10.3847/1538-4357/adda45
Cathryn M. Trott et al. 2025. Utilizing Gaussian information to enhance the limit of the 21 cm signal at z = 6.5–7.0 using Murchison wide field array data. APJ 991, 211; doi: 10.3847/1538-4357/adff80
Source: www.sci.news
