These Ghost-Town Galaxies Only Contain Super Old Stars, Meaning Something Mysterious Happened To Them In The Early Universe
Astronomers have investigated three ultra-faint dwarf galaxies that are located in a region of space far away from the influence of larger planetary objects.
The investigation was made possible by data from the DESI Legacy Imaging Surveys and the Gemini South telescope.
The galaxies were located in the direction of the spiral galaxy NGC 300 and only contained ancient stars, which backs up the theory that events in the early universe abruptly stopped star formation in the smallest galaxies.
Ultra-faint dwarf galaxies are the faintest types of galaxies in the universe. They usually contain a few hundred to a thousand stars, compared to the hundreds of billions that make up the Milky Way. These small structures tend to hide among the brighter galaxies in the sky.
Previously, astronomers have had the most luck detecting them near our own galaxy, the Milky Way. However, this doesn’t help improve their understanding of ultra-faint dwarf galaxies.
The Milky Way’s heat and gravitational forces can eradicate the dwarf galaxies’ gas and mess with how they evolve.
Beyond the Milky Way, ultra-faint dwarf galaxies have become too spread out for astronomers and traditional computer algorithms to uncover.
So, a manual search by eye was necessary to identify three faint and ultra-faint dwarf galaxies near NGC 300 and the Sculptor constellation.
“It was during the pandemic. I was watching TV and scrolling through the DESI Legacy Survey viewer, focusing on areas of the sky that I knew hadn’t been searched before. It took a few hours of casual searching, and then boom! They just popped out,” said David Sand, an astronomer from the University of Arizona.
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They were named the Sculptor galaxies. They are one of the first ultra-faint dwarf galaxies to be found in an isolated environment away from the influence of the Milky Way or other large structures.
The research team used the Gemini South telescope to examine the three galaxies in more detail. An analysis of the data revealed that they were devoid of gas and only contained super old stars, suggesting that their star formation was restrained a very long time ago.
The finding supports existing theories that ultra-faint dwarf galaxies are “stellar ghost towns” because their star formation was cut off sometime in the early universe.
Gas is required to trigger the formation of a new star, but ultra-faint dwarf galaxies don’t have enough gravity to hold onto the gas.
The Sculptor galaxies are far away from any larger galaxies, so no giant neighbors are around to steal their gas.
“We’ve found three of these galaxies, but that isn’t enough. It would be nice if we had 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 said.
The team is now working on training an artificial intelligence system to identify more galaxies of this kind. Hopefully, this tool will accelerate discoveries.
The study was published in Astrophysical Journal Letters.
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