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03-01-2024

Webb telescope discovers what powered the reionization of the universe

The James Webb Space Telescope (JWST) has made a cosmic discovery about reionization that unravels more of the mysteries of the universe’s first billion years.

An international team of scientists has successfully conducted the first spectroscopic observations of the universe’s faintest galaxies during this formative period, offering insights into a fundamental question that has puzzled astronomers for decades: what powered the reionization of the universe?

Decoding reionization and the dawn of the universe

The era of reionization marks a critical phase in the universe’s early history, a time when it was plunged into darkness, devoid of stars and galaxies, and enveloped in a dense hydrogen fog.

This period ended when the first stars ionized the surrounding gas, allowing light to traverse the cosmos. Determining the sources of radiation capable of clearing this primordial fog has been a key focus of astronomical research for years.

The UNCOVER program, which stands for Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization, utilized both imaging and spectroscopic techniques to study the lensing cluster Abell 2744, also known as Pandora’s Cluster.

The phenomenon of gravitational lensing, where the massive cluster acts as a ‘lens’ warping the space around it, magnifies and distorts the light from distant galaxies. This effect enabled the team to identify eight exceptionally faint galaxies beyond Abell 2744 that would otherwise remain hidden from view.

Discovery of ultra-faint galaxies

The revelations from this study are profound. The faint galaxies identified are found to be significant sources of ultraviolet light, emitting at levels four times greater than previously estimated.

This suggests that these dwarf galaxies were likely the primary contributors to the reionization process.

Iryna Chemerynska from the Institut d’Astrophysique de Paris highlights the critical role of these ultra-faint galaxies in the cosmic saga.

“This discovery unveils the crucial role played by ultra-faint galaxies in the early Universe’s evolution. They produce ionising photons that transform neutral hydrogen into ionised plasma during cosmic reionization. It highlights the importance of understanding low-mass galaxies in shaping the Universe’s history,” Chemerynska explained.

Echoing this sentiment, team leader Hakim Atek, also from the Institut d’Astrophysique de Paris, emphasizes the surprising efficiency of these galaxies.

“Despite their tiny size, these low-mass galaxies are prolific producers of energetic radiation. Their collective influence during this period was so substantial that they could transform the entire state of the Universe,” Atek explains.

Methodology and technological marvels

The team’s methodology involved an innovative combination of sensitive imaging data from Webb and the Hubble Space Telescope, focusing on selecting faint galaxy candidates from the epoch of reionization.

Following this, Webb’s Near-InfraRed Spectrograph (NIRSpec) played a pivotal role in capturing spectra of these galaxies, marking a significant milestone in our understanding of faint galaxies’ commonality and ionizing power during this epoch.

Hakim Atek further elaborates on the technical achievements that facilitated this discovery.

“The incredible sensitivity of NIRSpec, coupled with the gravitational amplification by Abell 2744, allowed us to explore these galaxies from the universe’s first billion years in unprecedented detail, despite being over 100 times fainter than our Milky Way,” Atek explained further.

Future explorations: The GLIMPSE program

Looking ahead, the GLIMPSE observing program aims to extend these findings by targeting another galaxy cluster, Abell S1063.

This future endeavor seeks to identify even fainter galaxies from the epoch of reionization, potentially confirming whether the dwarf galaxies studied are representative of the broader galaxy distribution.

As the current findings are based on a single field, further observations are necessary to validate these results and understand the ionizing properties of faint galaxies in different cosmic environments.

Cosmic reionization and the journey ahead

In summary, the Webb Telescope has opened a new chapter in our understanding of the universe’s earliest days, revealing the pivotal role of ultra-faint dwarf galaxies in the cosmic reionization process.

By harnessing the power of advanced imaging and spectroscopic techniques, astronomers have identified these elusive galaxies and measured their surprising contribution to the transformation of the universe from a dense hydrogen fog to a transparent cosmos.

As we stand on the brink of further discoveries with upcoming programs like GLIMPSE, the work of the international team of scientists underscores the importance of continued exploration and innovation in unraveling the mysteries of the cosmic dawn, marking a significant leap forward in our quest to comprehend the vast universe’s history and evolution.

More about reionization of the universe

As discussed above, reionization marks a pivotal epoch in the history of the universe, a transformative process that reshaped the cosmic landscape.

Following the Big Bang, the universe was in a hot, dense state, filled with a plasma of protons, electrons, and photons.

As it expanded and cooled, protons and electrons combined to form neutral hydrogen atoms, leading to the Cosmic Dark Ages, a period devoid of light, except for the fading glow of the Cosmic Microwave Background.

The era of reionization

The Era of Reionization began around 400,000 years after the Big Bang and is thought to have lasted until approximately one billion years post-Big Bang.

This epoch was characterized by the first stars and galaxies forming out of dense pockets of gas in the universe.

The intense ultraviolet light from these first luminous objects was powerful enough to ionize the surrounding neutral hydrogen, stripping electrons away from protons and thus ending the universe’s neutral phase.

Role of the first stars and galaxies

The first stars, often referred to as Population III stars, played a crucial role in this process. These stars were massive, hot, and short-lived, emitting a significant amount of ultraviolet radiation capable of ionizing hydrogen over vast distances.

As more stars and galaxies formed, their collective radiation contributed to the reionization process, creating bubbles of ionized gas that grew and overlapped, gradually filling the universe with ionized hydrogen.

Reionization had profound effects on the structure and evolution of the universe. By clearing the fog of neutral hydrogen, it allowed light to travel freely across the cosmos, making the universe transparent to ultraviolet light for the first time.

This epoch is crucial for understanding galaxy formation and evolution, as the process of reionization influenced the cooling of gas, star formation rates, and the growth of cosmic structures.

Observing reionization in the universe

Detecting signals from the Era of Reionization is a significant challenge, requiring innovative observational techniques.

Astronomers use a variety of methods to study this period, including observing distant quasars, the most luminous objects in the universe, whose light can reveal the conditions of the intervening gas.

The Cosmic Microwave Background also provides indirect evidence of reionization, showing slight variations in temperature that indicate the presence of ionized regions.

Advancements in telescope technology and observational techniques promise to shed more light on this enigmatic period.

Projects like the James Webb Space Telescope and ground-based observatories aim to peer deeper into the universe’s history, capturing the light from the first stars and galaxies and further unraveling the mysteries of reionization.

The study of reionization not only enriches our understanding of the universe’s early days but also offers insights into the fundamental processes that have shaped the cosmos.

As we continue to explore this critical epoch, we move closer to answering some of the most profound questions about the origins and evolution of the universe.

The full study was published in the journal Nature.

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