Astronomy, always seeking the deepest mysteries of the cosmos, has taken a significant new step with the discovery of three ultra-faint dwarf galaxies. This breakthrough, the result of collaboration between powerful telescopes in Chile and an international team of scientists, sheds light on events in the early Universe that influenced star formation in the smallest galaxies.
Ultra-faint dwarf galaxies are, as their name suggests, the faintest structures in the cosmos. They contain only hundreds or thousands of stars—a negligible number compared to the hundreds of billions of stars that make up galaxies like the Milky Way. These tiny galaxies are often hidden among the brighter objects in the sky, making their detection a real challenge. Until now, most of these objects had been identified near the Milky Way, where gravitational forces and interaction with its galactic halo significantly influence their evolution.
The recent discovery is remarkable because the identified galaxies are located in an isolated region, far from the gravitational influence of larger structures. These galaxies, called Sculptor galaxies, were detected through manual analysis by David Sand, an astronomer at the University of Arizona, who examined sky images captured by the DECam Legacy Survey (DECaLS). This meticulous effort led to the identification of these galaxies in the direction of the Sculptor constellation, near the spiral galaxy NGC 300.
The role of the telescopes at Cerro Tololo and Pachón was crucial to this finding. The Gemini South telescope and the Dark Energy Camera (DECam), installed on the Víctor Blanco Telescope, provided high-quality data that enabled detailed analysis of the galaxies. Instruments such as the Gemini South Multi-Object Spectrograph (GMOS) delivered images confirming that these galaxies are composed solely of very old stars and lack gas, an essential element for forming new stars.
The discovery supports the hypothesis that events in the early Universe, such as the Epoch of Reionization, may have disrupted star formation in small galaxies. During this period, intense ultraviolet radiation heated and dispersed gas in many young galaxies, leaving ultra-faint dwarf galaxies as cosmic “ghost towns”. Another possible explanation is that early supernova explosions expelled the gas needed to form new stars.
If reionization is the culprit, these galaxies could offer a window into studying the early Universe: We don’t know how powerful or uniform this reionization effect was, but it could be that reionization was irregular and didn’t occur everywhere at the same time. We’ve found three galaxies of this kind, but it’s not enough. It would be great to have hundreds of them. If we knew what fraction was affected by reionization, that would tell us something about the early Universe that is very difficult to probe otherwise, Sand explained.
To advance in this field, Sand’s team is training artificial intelligence systems to identify more ultra-faint dwarf galaxies in the vast catalogs of astronomical data. This approach promises to accelerate discoveries and open new windows into the study of the early Universe.
SOURCES
David J. Sand et al., Three Quenched, Faint Dwarf Galaxies in the Direction of NGC 300: New Probes of Reionization and Internal Feedback. ApJL 977 L5. DOI 10.3847/2041-8213/ad927c
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