By about 1 billion years after the Big Bang, the end of the period known as the cosmic dawn, the Universe was entirely reionized.
But because there’s so much murk in the cosmic dawn, and because it’s so dim and far away across time and space, we’ve had trouble seeing what’s there.
JWST was designed, in part, to peer into the cosmic dawn and try to see what lurks therein.
Surprisingly, the telescope’s observations now suggest that dwarf galaxies are the key player in reionization.
This allowed the researchers to see tiny dwarf galaxies close to the cosmic dawn.
We now know what illuminated the early Universe’s dark, formless emptiness.
Early cosmic dawn data from the Hubble and James Webb Space Telescopes suggests that the free-flying photons came from tiny dwarf galaxies that flared to life, removing the haze of hazy hydrogen that surrounded intergalactic space. In February 2024, a paper detailing the research was released.
At the Institut d’Astrophysique de Paris, astrophysicist Iryna Chemerynska stated, “This discovery reveals the crucial role played by ultra-faint galaxies in the early Universe’s evolution.”.
“During cosmic reionization, they generate ionizing photons that convert neutral hydrogen into ionized plasma. It emphasizes how crucial it is to comprehend how low-mass galaxies shaped the history of the Universe. “..”.
Minutes after the Big Bang, a hot, thick fog of ionized plasma filled space at the beginning of the Universe. Photons would have simply scattered off the free electrons floating around, effectively making the universe dark, and what little light there was would not have been able to penetrate this fog.
After roughly 300,000 years, as the universe cooled, protons and electrons started to combine to create neutral hydrogen gas, along with a small amount of helium.
There weren’t many light sources to create it, but the majority of light wavelengths could pass through this neutral medium. However, the first stars were formed from this hydrogen and helium.
The radiation from those early stars was powerful enough to reionize the gas and separate electrons from their nuclei. However, the universe had gotten so big by now that the gas was diffuse and could not stop light from shining.
When the cosmic dawn period ended, approximately 1 billion years after the Big Bang, the Universe was completely reionized. Finally, the lights came on.
However, we have had difficulty seeing what is there because the cosmic dawn is so murky, the light is so dim, and it is so far away across time and space.
Scientists believed that the massive black holes whose accretion produces blazing light and massive galaxies in the midst of star formation (baby stars produce a lot of UV light) must have been the sources that caused the majority of the clearing.
Part of the reason JWST was built was to look into the cosmic dawn and see what might be there. It’s been incredibly successful, bringing to light a variety of unexpected facts about this pivotal period in the universe’s formation. Contrary to expectations, the telescope’s observations now point to dwarf galaxies as the primary cause of reionization.
With the support of Hubble data, a multinational team headed by astrophysicist Hakim Atek of the Institut d’Astrophysique de Paris used JWST data on a galaxy cluster known as Abell 2744.
Because Abell 2744 is so dense, space-time distorts around it, creating a cosmic lens that magnifies any light from afar that comes to us through that space-time. As a result, the researchers were able to observe small dwarf galaxies near the cosmic dawn.
They then acquired detailed spectra of these small galaxies using JWST. In addition to being the most prevalent galaxy type in the early Universe, their analysis showed that these dwarf galaxies are significantly brighter than anticipated.
As the team’s research reveals, dwarf galaxies are 100 times more numerous than large galaxies, and their combined output is four times the ionizing radiation typically thought of for larger galaxies.
“The combined energy of these cosmic powerhouses is more than sufficient to complete the task,” Atek stated.
“These low-mass galaxies, despite their small size, are very active sources of energetic radiation, and they are so abundant at this time that their combined impact has the power to change the Universe as a whole. “,”.
Although it’s the strongest proof yet for the reionization force, more research is still needed. Researchers must ensure that their sample is representative of the entire population in the cosmic dawn and not just an anomalous cluster of dwarf galaxies, as they only examined a small portion of the sky.
Their goal is to gather a larger sample of early galactic populations by investigating additional cosmic lens regions of the sky. However, the results are extremely exciting for this single sample. Since the beginning of our knowledge of reionization, scientists have been searching for answers. Finally dispelling the fog is about to happen.
Astrophysicist Themiya Nanayakkara of Swinburne University of Technology in Australia stated, “With the JWST, we have now entered uncharted territory.”.
“This work raises more fascinating questions that we must address in order to map out the evolutionary history of our origins. “.”.
Nature has published the study.
This article was first published in March 2024.
