Investigating the Galaxies Responsible for the Reionization of the Universe with Hubble and Webb

Utilizing the powerful instruments of the James Webb Space Telescope, scientists have made groundbreaking discoveries about the oldest galaxies in the universe. These galaxies, believed to have been formed during the first one billion years of the universe, provide valuable insight into the reionization period when hydrogen gas covered the universe before the first stars began ionizing it.

Astronomers have long sought to identify the sources that emitted radiation capable of clearing the hydrogen fog. The new observations from the James Webb Space Telescope, in combination with data from the Hubble Space Telescope, are shedding light on these elusive sources. The observations were part of the Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization (UNCOVER) program. The scientists focused on Abell 2744, also known as Pandora’s Cluster, a giant galaxy cluster located approximately four billion light-years from Earth.

A unique feature of Abell 2744 is its ability to create gravitational lensing, a phenomenon where the fabric of spacetime is warped by its immense gravitational forces. The cluster bends and distorts light from objects within and around it, allowing scientists to study faint and distant galaxies that would otherwise remain undetectable. Through gravitational lensing, the scientists were able to identify and study eight extremely distant and faint galaxies.

What surprised the scientists was that these distant galaxies are producing four times more ultraviolet (UV) light than previously expected. Despite their small size compared to full-size galaxies, these dwarf galaxies are emitting significant amounts of energy. This discovery has important implications for understanding the role of ultra-faint galaxies in shaping the early universe’s evolution and its reionization.

To study these galaxies, the scientists combined infrared images from the James Webb Space Telescope with images from the Hubble Space Telescope. This allowed them to identify extremely faint galaxy candidates from the period of reionization. Using Webb’s Near Infrared Spectrograph (NIRSpec) instrument, the team performed spectroscopy on these candidates and collected multiple spectra using NIRSpec’s multi-shutter assembly. These observations confirmed the abundance of these faint galaxies during the epoch of reionization and revealed their true ionizing power.

The sensitivity of NIRSpec, combined with the gravitational amplification provided by Abell 2744, allowed scientists to study these galaxies in detail, despite them being over 100 times fainter than our own Milky Way. The upcoming GLIMPSE program will further investigate faint galaxies by observing another galaxy cluster, Abell S1063. If similar galaxies are found in Abell S1063, it will confirm their role in the epoch of reionization.

These findings pave the way for future observations and studies of galaxy clusters. Scientists hope to continue supporting the hypothesis that these faint dwarf galaxies were responsible for the reionization of the universe. Additionally, further observations will allow astronomers to explore the Cosmic Dawn, a period when the first galaxies began to form.

The study conducted by Atek et al. has been published in the journal Nature. This remarkable research opens new doors to understanding the early universe and the crucial role played by ultra-faint galaxies in its evolution. The James Webb Space Telescope continues to unlock mysteries of the universe, pushing the boundaries of scientific discovery.