Amidst the vast universe, solitary galaxies actually gather in clusters, bound together by their shared gravity. Surprisingly, at times, they even consume each other.
Put simply, larger galaxies merge with and consume smaller ones, growing even larger. The Milky Way galaxy itself cannibalized a neighboring galaxy, gaining supremacy about 10 billion years ago.
And what of the smaller galaxies being shredded by their larger counterparts? While some vanish, new research reveals that dense tiny galaxies are capable of powering through. These mighty realms maintain their cores and transform into Ultra Compact Dwarfs, or UCDs, as astronomers call them.
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Researchers recently used the Gemini North Telescope near the Mauna Kea mountain in Hawaii, and they observed galactic cannibalism near the Virgo Cluster, which is relatively close to Earth. For the first time, they saw small galaxies transitioning into UCDs. About 106 galaxies displayed far-reaching envelopes of stars, indicating that their outer layers were being torn apart by larger galaxies. However, groupings of stars in their centers suggested that their gravitational hold was strong enough to survive the merger.
Once the stars and gas in the galaxies’ outer layers are fully removed, it is expected that these tiny galaxies will become late-stage UCDs.
“It’s exciting that we can finally see this transformation in action,” said Eric Peng, an astronomer at National Optical-Infrared Astronomy Research Laboratory, in a statement. “It tells us that many of these UCDs are visible fossil remnants of ancient dwarf galaxies in galaxy clusters, and our results suggest that there are likely many more low-mass remnants to be found.”
Peng and his team first spotted these candidate UCD progenitors using images taken by the Canada–France–Hawaii Telescope, also located near the summit of Hawaii’s Mauna Kea mountain. However, discerning the target galaxies from other distant galaxies in the original images was challenging.
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Therefore, the team conducted follow-up observations using Gemini North to accurately measure galaxy distances, and they removed background galaxies to focus solely on the candidate UCDs within the Virgo Cluster. The results revealed that these UCDs were “almost exclusively near the largest galaxies,” said Kaixiang Wang, the study’s lead author and a scientist at Peking University in China. “We immediately knew that environmental transformation had to be important.”
This research was detailed in a paper published Wednesday (Nov. 8) in the journal Nature.
