Astronomers observed the deteriorating remnants of 100 dwarf galaxies violently stripped of stars by larger counterparts, revealing a crucial link in the evolution of ultra-compact dwarf galaxies (UCDs).
This finding indicates that UCDs, known for their extreme stellar density, are essentially fossilized remnants of ordinary dwarf galaxies destroyed in intense gravitational interactions with larger galaxies.
What Are Ultra-Compact Dwarf Galaxies?
UCDs, a recently identified class of stellar systems found in the central regions of nearby galaxy clusters, boast aging stellar populations and surpass the size, brightness, and mass of the largest Milky Way globular clusters (GCs), yet exhibit greater compactness compared to typical dwarf galaxies of similar luminosity.
Discovered over two decades ago, UCDs have perplexed astronomers due to their smaller size compared to ordinary dwarf galaxies and larger size than closely resembling star clusters. While scientists initially theorized that UCDs were remnants of destroyed dwarf galaxies, the absence of an intermediate galaxy hindered confirmation of this transition.
Recent investigations show that UCDs have a mass-to-light ratio (M/L) that is twice as large as GCs with similar metal content. It suggests that many UCDs have M/L ratios higher than what standard stellar mass functions predict, indicating the presence of stellar populations with extreme mass distributions or that UCDs might be small-scale concentrations of dark matter. This finding provides new opportunities for investigating how dark matter particles cluster together.
Transforming Dwarf Galaxies in Virgo Cluster Illuminates Cosmic Evolution Mysteries
Using the Gemini North telescope in Hawai'i, astronomers explored the home of over 2,000 galaxies from 65 million light-years away known as the Virgo Cluster.
In their research, titled "An evolutionary continuum from nucleated dwarf galaxies to star clusters" published in the journal Nature, the team reported dozens of dwarf galaxies amid a transformation, shedding light on a class of galaxies discovered almost 25 years ago.
Eric Peng, an astronomer at the Kavli Institute for Astronomy and Astrophysics at Peking University, explained that the findings offer a comprehensive view of the origin of these mysterious galaxies, establishing a continuum bridging the size gap between star clusters and galaxies.
The newly identified galaxies in the Virgo Cluster appear to be in the early stages of forming UCDs and are situated near massive galaxies. The gravitational influence of these nearby giants seems to be stripping the smaller cosmic objects of their stars and gas.
Observations also revealed objects within the Virgo Cluster exhibiting stretched and diffuse envelopes of gas and stars, indicating ongoing gravitational influence. Lead author Laixiang Wang, a scientist at Peking University, emphasized the significance of environmental transformation in this process, highlighting the exclusive proximity of these transition galaxies to the largest galaxies in the cluster.
By arranging the observations into a time sequence, the astronomers obtained a glimpse into the evolving story of these galaxies losing stars. Peng expressed excitement about witnessing this transformation, suggesting that many UCDs are visible remnants of ancient dwarf galaxies within galaxy clusters. The findings imply the likelihood of discovering numerous additional low-mass remnants in the future.
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