An early hint of cosmic dawn has been seen in a distant galaxy

Earliest Galaxy Hints at Dawn of Cosmic Reionisation

Researchers have identified a galaxy from the universe’s infancy, potentially offering the earliest evidence of cosmic reionisation. This pivotal epoch marked the first time the cosmos became luminous.

Unveiling the Reionisation Epoch

In the aftermath of the Big Bang, the nascent universe was filled with hot hydrogen and helium gas. This pervasive gas diffused photons, rendering the cosmos somewhat opaque. As stars began to emerge over subsequent millions of years, their emitted light ionised the surrounding hydrogen and helium. This ionisation process allowed photons to traverse freely, thereby making the universe transparent. However, the precise timing of this cosmic dawn remains a subject of investigation.

James Webb Telescope Observes Ancient Galaxy

Utilising the James Webb Space Telescope (JWST), Joris Witstok and his team at the University of Copenhagen in Denmark conducted a study on a galaxy designated JADES-GS-z13-1-LA. This galaxy is observed as it existed 330 million years after the Big Bang, positioning it among the most primordial galaxies known in the universe.

Evidence of a Cosmic Bubble

Analysis of ultraviolet radiation emanating from JADES-GS-z13-1-LA suggests it is enveloped by a vast bubble, spanning approximately 200,000 light-years. This expansive bubble is theorised to have formed from the interaction of the galaxy’s starlight with the surrounding hydrogen in space. Witstok remarked that witnessing indicators of reionisation so early in the universe surpassed their “wildest expectations.”

Confirmation and Excitement in the Scientific Community

Michele Trenti at the University of Melbourne corroborated that these observations align with the cosmic reionisation process. Trenti expressed both surprise and excitement, stating, “It’s both surprising and exciting. I would not expect the ultraviolet light emitted from this galaxy to reach JWST. The cold neutral hydrogen gas that we were expecting would have surrounded the galaxy should have blocked the photons. We are witnessing the onset of reionisation.”

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Galaxy’s Nature Still Under Scrutiny

The precise nature of this diminutive galaxy remains uncertain. Its intense luminosity could stem from a population of massive, young, and intensely hot stars or potentially from a powerful supermassive black hole at its core. Trenti added, “This would be the earliest known evidence for a supermassive black hole situated at the centre of a galaxy.”

Benchmark for Early Galaxy Studies

While comparable bubbles have been detected around galaxies at later cosmic epochs, JADES-GS-z13-1-LA represents the earliest documented instance. Richard Ellis at University College London highlighted its significance as a “benchmark.” He elaborated, “It tells us that this galaxy must have been around for quite a while, and pushes that little bit further back to the beginning of when galaxies first emerged from darkness.”

Future Observations and Further Discoveries

The JWST’s ability to unveil details about this galaxy was achieved through a prolonged observation period of approximately 19 hours. Witstok conveyed optimism about uncovering additional early signs of cosmic reionisation in the near future. “We have a few more candidates,” he mentioned. “We might find it even further [back in time], or maybe this is the most extreme that it gets.”