Scientists studying data collected by the James Webb Space Telescope believe they have identified extremely bright galaxy clusters formed in the redshift 7 phase of the galaxy’s development as the source of extreme levels of ultraviolet light that powered a period of cosmic renovation known as reionization.
The mysterious origins of this reionization process have long baffled astronomers and cosmologists. The new research says these small, yet powerful galaxies underwent extreme star formation events called starbursts that were able to generate sufficient ultraviolet light to clear a path through the universe’s early interstellar galactic clouds, resulting in reionization.
“When it comes to producing ultraviolet light, these small galaxies punch well above their weight,” explained Isak Wold, an assistant research scientist at Catholic University of America in Washington and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Our analysis of these tiny but mighty galaxies is 10 times more sensitive than previous studies, and shows they existed in sufficient numbers and packed enough ultraviolet power to drive this cosmic renovation.”
James Webb Telescope Leads Hunt for Cosmic Reionization
Although the universe spent its first billion or so years engulfed in a fog of neutral hydrogen gas, today this gas has been stripped of its electrons, or ionized. Astronomers have proposed several causes of this period of cosmic renovation, including big galaxies, small galaxies, and even black holes. Still, no definitive reionization cause has been conclusively identified.
Since recent studies have pointed to smaller galaxies as the likely culprit for the extreme ultraviolet light driving reionization, the team searched through previously recorded James Webb Space Telescope data for galaxies of the right cosmic age showing signs of starbursts powerful enough to produce outsized amounts of ultraviolet light.
“Low-mass galaxies gather less neutral hydrogen gas around them, which makes it easier for ionizing ultraviolet light to escape,” Rhoads said. “Likewise, starburst episodes not only produce plentiful ultraviolet light — they also carve channels into a galaxy’s interstellar matter that helps this light break out.”
According to the study’s authors, two of Webb’s instruments, the NIRCam (Near-Infrared Camera) and NIRSpec (Near-Infrared Spectrograph), are ideally suited to studying the infrared light from the galaxy’s ancient star formation phase, called redshift 7, that has crossed the cosmos.
Gravitational Lens Brings Objects 4 Billion Light Years Away into Focus
The team started the study by scouring the NIRCam data for strong sources of high-energy processes powerful enough to generate a green line emitted by oxygen atoms after they lose two electrons. Originally in the visible spectrum, the eons spent crossing the cosmos have stretched this light out, resulting in an infrared signal detectable by the James Webb Space Telescope.
Using a process called gravitational lensing to increase Webb’s resolution, the team focused on data gathered from a giant galaxy cluster called Abell 2744. Located about 4 billion light years from Earth, Abell 2744 is nicknamed Pandora’s cluster.
By comparing captured as part of the UNCOVER (Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization) observing program, led by Rachel Bezanson at the University of Pittsburgh in Pennsylvania, with new readings of the same region collected by NIRSpec, the team identified 83 candidate starburst clusters. Because all of these clusters formed around 800 million years after the Big Bang, they fall into the redshift 7 period.
“These galaxies are so small that, to build the equivalent stellar mass of our own Milky Way galaxy, you’d need from 2,000 to 200,000 of them,” Malhotra said. “But we are able to detect them because of our novel sample selection technique combined with gravitational lensing.”
After focusing on 20 of these clusters for “deeper inspection,” Wold and colleagues from NASA’s Goddard Space Flight Center, Sangeeta Malhotra and James Rhoads, found evidence of extreme star formation and outsized ultraviolet light production. Although tiny in size, the stars similar to those in the present-day universe “release about 25% of their ionizing ultraviolet light into surrounding space.”
Wold says if the galaxy clusters his team studied release a similar amount of ultraviolet light, they can account for all of the ultraviolet light needed to convert the universe’s neutral hydrogen to its ionized form.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.