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For hundreds of a millions of years, the universe existed in the dark ages—an epoch when only primordial gasses existed.
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Then, a period of reionization, cleared away this foggy existence an introduced light into the universe.
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Now, an international team of scientists at the helm of the James Webb Space Telescope have analyzed eight of the faintest dwarf galaxies that existed during this time, and determined that these galaxies produced enough radiation to kickstart the reionization process.
While the “Epoch of Reionization” sounds like the title of a sci-fi novel destined for a Hugo award, this very real era of the universe featured the first light from the very first stars. Before this epoch, the universe was nothing more than a dark void filled with a fog of primordial hydrogen gas—and then, suddenly, there was light.
For decades, scientists have searched for a source of radiation powerful enough to have cleared away this fog and introduced light into the universe. Now, an international team of scientists have analyzed the first faintest galaxies (which existed in the universe’s first billion or so years) and identified certain dwarf galaxies that are likely responsible for producing the some of the first photons that heralded the reionization epoch. The results of the study were published in the journal Nature.
“This discovery unveils the crucial role played by ultra-faint galaxies in the early Universe’s evolution,” Iryna Chemerynska, an astrophysicist at the Institut d’Astrophysique de Paris in France and co-author of the study, said in a press statement. “They produce ionizing photons that transform neutral hydrogen into ionized plasma during cosmic reionization. It highlights the importance of understanding low-mass galaxies in shaping the Universe’s history.”
Detecting these ultra-faint galaxies is no easy feat—in fact, it required the $10 billion dollar James Webb Space Telescope (JWST). This work is part of the Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) program, which (as its name suggests) leverages the telescope’s near-infrared camera and near-infrared spectrograph to investigate the oldest known dwarf galaxies in the universe. To achieve this, astronomers used a technique known as “gravitational lensing,” which uses the curvature of spacetime around massive objects as a lens.
The “massive object” in question is the lensing cluster Abell 2744, also known as Pandora’s cluster, which is actually an amalgamation of at least four smaller galaxy clusters. Thanks to this cluster’s magnification effect, the team detected light sources from eight extremely faint galaxies.
“The incredible sensitivity of NIRSpec combined with the gravitational amplification provided by Abell 2744 enabled us to identify and study these galaxies from the first billion years of the Universe in detail, despite their being over 100 times fainter than our own Milky Way,” Hakim Atek, an astrophysicist from Sorbonne University who led the study, said in a press release. “Despite their tiny size, these low-mass galaxies are prolific producers of energetic radiation, and their abundance during this period is so substantial that their collective influence can transform the entire state of the Universe.”
This discovery showcases the incredible power of JWST. Scientists first captured ultra-deep imaging data and followed that analysis with a spectroscopy with NIRSpec. Using this instrument’s Multi-Shutter Assembly, the team successfully captured multi-object spectroscopy of these extremely faint galaxies. This is the first time that these galaxies have been imaged in such detail, and the first time scientists were able to confirm that they produced enough radiation to end the light-less tyranny of the early universe’s swirling primordial gas.
This is only the beginning of how far back JWST could potentially study. For instance, there’s another program for which Atek is a principal investigator called GLIMPSE, which (extremely obliquely) stands for… deep breath… “gravitational lensing & NIRCam imaging to probe early galaxy formation and sources of reionization.” The program hopes to explore an era known as the Cosmic Dawn, when the universe was only a few million years old.
Who needs time travel when you have a space telescope like JWST?
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