Using data from the James Webb Space Telescope (JWST), astronomers have discovered a population of dozens of small galaxies. They played a key role in the cosmic “renewal” that transformed the early Universe into the one we know today.
For most of its first billion years, the Universe was shrouded in a fog of neutral hydrogen. Today, this gas is ionized — devoid of electrons. Astronomers, who call this transformation reionization, have long wondered what types of objects are most responsible for it: large galaxies, small galaxies, or supermassive black holes in active galaxies.
To answer this question, researchers used the JWST. However, there was one problem. Even the capabilities of the JWST are insufficient to see the tiny galaxies that existed at the dawn of the Universe. Therefore, astronomers used a gravitational lens — the Abell 2744 galaxy cluster, located about 4 billion light-years away in the southern constellation Sculptor. Its powerful gravity amplified the brightness of more distant background objects, enabling JWST to see them.
The scientists focused on small galaxies demonstrating processes of intense star formation. For this purpose, they searched for strong light sources of a specific wavelength that indicate the presence of high-energy processes: the green line emitted by oxygen atoms that have lost two electrons. Originally emitted as visible light in the early Universe, the green glow from doubly ionized oxygen stretched into the infrared range as it passed through the expanding Universe, eventually reaching the JWST instruments.
This approach enabled the discovery of 83 small galaxies with explosive star formation that existed when the Universe was 800 million years old, or about 6% of its current age. They are so small that it would take between 2,000 and 200,000 such galaxies to create a stellar mass equivalent to that of our Milky Way.
According to researchers, such types of galaxies in the modern Universe emit about 25% of their ionizing ultraviolet radiation into the surrounding space. If low-mass galaxies with flares of star formation in the past produced a similar amount, they could well have provided all the ultraviolet radiation necessary to convert neutral hydrogen into its ionized form. So, these objects were the ones that played a key role in the Cosmic Dawn era, when the Universe got its current look.
Earlier, we reported that scientists had proposed an alternative explanation for the nature of relic radiation.
According to NASA
