Free Astronomy Magazine January-February 2024

30 JANUARY-FEBRUARY 2024 ASTRO PUBLISHING by NOIRLab Josie Fenske U ltra-compact dwarf galaxies (UCDs) are among the densest stellar groupings in the Uni- verse. Being more compact than other galaxies with similar mass, but larger than star clusters — the ob- jects they most closely resemble — these mystifying objects have defied classification. The missing piece to this puzzle has been a lack of suffi- cient transitional, or intermediate objects to study. A new galaxy sur- vey, however, fills in these missing pieces to show that many of these enigmatic objects are likely formed from the destruction of dwarf galaxies. The idea that UCDs are remnants of disrupted dwarf galaxies has been proposed since they were discov- ered over two decades ago. How- ever, previous searches have not revealed the large population of galaxies-in-transition that you would expect to find. So an interna- tional team of astronomers con- ducted a systematic search for these intermediate-stage objects around the Virgo Cluster, a grouping of thousands of galaxies in the direc- tion of the constellation Virgo. T his illustration shows a dwarf galaxy in the throes of transitioning to an ultra-compact dwarf galaxy as it’s stripped of its outer layers of stars and gas by a nearby larger galaxy. Ultra-compact dwarf galaxies are among the densest stellar groupings in the Universe. Being more compact than other galaxies with similar mass, but larger than star clusters — the objects they most closely resem- ble — these mystifying objects have defied classification. The missing piece to this puzzle has been a lack of sufficient transitional, or intermediate objects to study. A new galaxy survey, however, fills in these missing pieces to show that many of these enigmatic objects are likely formed from the destruction of dwarf galaxies. [NOIRLab/NSF/AURA/M. Zamani] Gemini North unveils the formation of dense dwarf galaxy ‘fossils’