Mysterious Dwarf Galaxies in the Hydra Cluster Leave Scientists Stunned: ‘We Discovered the Unexpected’

Astronomers have made an unexpected discovery about a unique type of galaxy known as Ultra-Diffuse Galaxies (UDGs), which are some of the faintest and smallest galaxies in the universe. A research team investigating these galaxies found that nearly half of the UDGs they studied exhibited unusual movements that challenge earlier ideas about how galaxies develop and change over time. Specifically, many of these dwarf galaxies were noted to have unexpected rotational motion among their stars.

The research team focused on 30 UDGs located in the Hydra galaxy cluster, which is situated more than 160 million light-years away from Earth. The findings from this study could significantly alter our understanding of how these faint galaxies come into being and evolve over time. Chiara Buttitta, a researcher from the National Institute for Astrophysics and a co-author of the study, expressed her excitement about the results, noting that not only did the team succeed in identifying the motions of stars in these very faint galaxies, but they also stumbled upon surprising observations that were not anticipated.

To obtain these results, the team used an observing program called “Looking into the faintest With MUSE,” also known as LEWIS, which utilizes the MUSE integral field spectrograph. This high-tech instrument is housed on the Very Large Telescope (VLT), the most sophisticated visible-light observatory in the world, located in Chile.

Ultra-Diffuse Galaxies were first identified in 2015, and their unusual formation and characteristics immediately posed questions for astronomers. The LEWIS project enabled the researchers to determine that UDGs exist in environments with diverse properties, including varying levels of dark matter and different behaviors and compositions of stars.

The team conducted a detailed observation of a specific UDG named UDG32, which is located at the end of a gas filament connected to a larger spiral galaxy called NGC 3314A. A theory about how UDGs form suggests they could be created from gas dragged away from larger galaxies through gravitational forces. If this gas accumulates in certain areas, it may become thick enough to collapse and form stars, leading to the birth of a UDG.

The observations through the LEWIS program confirmed that UDG32’s position in relation to NGC 3314A is not just a random coincidence. Interestingly, UDG32 also contains more heavy elements, often referred to as “metals,” compared to other UDGs within the Hydra cluster. Metals are produced in stars and released into space when they explode at the end of their life cycle, serving as the building blocks for new stars. This finding is intriguing because the stars in UDG32 are younger than those found in other UDGs in the same region, yet they possess greater metal content. This suggests that UDG32 may have formed from gas enriched by an older galaxy, supporting the idea that it originated from its neighboring spiral galaxy.

The results from this research validate the goals of the LEWIS project, which has effectively doubled the number of UDGs analyzed using spectroscopic methods. Moreover, it has provided the first comprehensive overview of these faint galaxies within a galaxy cluster that is still in the process of forming. Enrichetta Iodice, the scientific director of the LEWIS project, highlighted the program’s potential as a wealth of data, noting the importance of being able to study numerous aspects of each galaxy, including star motions and stellar populations.

By piecing together the individual findings, researchers aim to reconstruct the formation history of these galaxies, which could reveal vital information about their properties and the dark matter that may reside within them. The team’s research has been documented in two papers published in the journal Astronomy & Astrophysics.