Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1
Owing to sparse spectroscopic observations, the classification of faint satellites as either dark-matter-dominated dwarf galaxies or self-gravitating star clusters remains unresolved. The recently discovered Ursa Major III/UNIONS 1 (UMa3/U1) object, with its measured velocity dispersion, provides a...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/2041-8213/adf320 |
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| author | Ali Rostami-Shirazi Hosein Haghi Akram Hasani Zonoozi Pavel Kroupa |
| author_facet | Ali Rostami-Shirazi Hosein Haghi Akram Hasani Zonoozi Pavel Kroupa |
| author_sort | Ali Rostami-Shirazi |
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| description | Owing to sparse spectroscopic observations, the classification of faint satellites as either dark-matter-dominated dwarf galaxies or self-gravitating star clusters remains unresolved. The recently discovered Ursa Major III/UNIONS 1 (UMa3/U1) object, with its measured velocity dispersion, provides a rare observational anchor in this regime. Despite its cluster-like compactness, its inferred dynamical mass-to-light ratio ( M _Dyn / L ) suggests a dark-matter-dominated nature, prompting interpretations of UMa3/U1 as a microgalaxy, though current measurements remain inconclusive. Thousand-level M _Dyn / L values are not unique to galaxies; self-gravitating dark star clusters (DSCs) can reach comparable levels via energy injection driven by a centrally segregated black hole subsystem (BHSub), which accelerates the evaporation of luminous stars and leads to a supervirial appearance with elevated velocity dispersion. To assess whether UMa3/U1 is a DSC, we conducted direct N -body simulations and identified a model that successfully reproduces both its compact structure and elevated M _Dyn / L , supporting a self-gravitating cluster origin. We find the cluster entered the DSC phase around 4 Gyr ago, with its luminous stars expected to be depleted within the next 1 Gyr, followed by the gradual disruption of the central BHSub over the subsequent Gyr. We broaden our analysis by mapping DSC evolutionary tracks in the size versus total luminosity ( L ) and M _Dyn / L – L spaces, showing that DSCs occupy a region overlapping with faint, ambiguous satellites. In the M _Dyn / L – L diagram, DSCs trace a transitional channel bridging globular clusters and dwarf galaxies as they rise from M _Dyn / L ≈ 2 to 10 ^4 M _⊙ / L _⊙ . |
| format | Article |
| id | doaj-art-59faaeb712e44faf9b6bcd3fb944f781 |
| institution | Kabale University |
| issn | 2041-8205 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-59faaeb712e44faf9b6bcd3fb944f7812025-08-20T03:41:11ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019891L1410.3847/2041-8213/adf320Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1Ali Rostami-Shirazi0https://orcid.org/0009-0001-8222-9436Hosein Haghi1https://orcid.org/0000-0002-9058-9677Akram Hasani Zonoozi2https://orcid.org/0000-0002-0322-9957Pavel Kroupa3https://orcid.org/0000-0002-7301-3377Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS) , 444 Prof. Sobouti Blvd., Zanjan 45137-66731, Iran ; a.rostami@iasbs.ac.ir, Haghi@iasbs.ac.irDepartment of Physics, Institute for Advanced Studies in Basic Sciences (IASBS) , 444 Prof. Sobouti Blvd., Zanjan 45137-66731, Iran ; a.rostami@iasbs.ac.ir, Haghi@iasbs.ac.ir; Helmholtz-Institut für Strahlen-und Kernphysik (HISKP) , Universität Bonn, Nussallee 14-16, D-53115 Bonn, GermanyDepartment of Physics, Institute for Advanced Studies in Basic Sciences (IASBS) , 444 Prof. Sobouti Blvd., Zanjan 45137-66731, Iran ; a.rostami@iasbs.ac.ir, Haghi@iasbs.ac.ir; Helmholtz-Institut für Strahlen-und Kernphysik (HISKP) , Universität Bonn, Nussallee 14-16, D-53115 Bonn, GermanyHelmholtz-Institut für Strahlen-und Kernphysik (HISKP) , Universität Bonn, Nussallee 14-16, D-53115 Bonn, Germany; Charles University in Prague , Faculty of Mathematics and Physics, Astronomical Institute, V Holešovičkách 2, CZ-180 00 Praha 8, Czech RepublicOwing to sparse spectroscopic observations, the classification of faint satellites as either dark-matter-dominated dwarf galaxies or self-gravitating star clusters remains unresolved. The recently discovered Ursa Major III/UNIONS 1 (UMa3/U1) object, with its measured velocity dispersion, provides a rare observational anchor in this regime. Despite its cluster-like compactness, its inferred dynamical mass-to-light ratio ( M _Dyn / L ) suggests a dark-matter-dominated nature, prompting interpretations of UMa3/U1 as a microgalaxy, though current measurements remain inconclusive. Thousand-level M _Dyn / L values are not unique to galaxies; self-gravitating dark star clusters (DSCs) can reach comparable levels via energy injection driven by a centrally segregated black hole subsystem (BHSub), which accelerates the evaporation of luminous stars and leads to a supervirial appearance with elevated velocity dispersion. To assess whether UMa3/U1 is a DSC, we conducted direct N -body simulations and identified a model that successfully reproduces both its compact structure and elevated M _Dyn / L , supporting a self-gravitating cluster origin. We find the cluster entered the DSC phase around 4 Gyr ago, with its luminous stars expected to be depleted within the next 1 Gyr, followed by the gradual disruption of the central BHSub over the subsequent Gyr. We broaden our analysis by mapping DSC evolutionary tracks in the size versus total luminosity ( L ) and M _Dyn / L – L spaces, showing that DSCs occupy a region overlapping with faint, ambiguous satellites. In the M _Dyn / L – L diagram, DSCs trace a transitional channel bridging globular clusters and dwarf galaxies as they rise from M _Dyn / L ≈ 2 to 10 ^4 M _⊙ / L _⊙ .https://doi.org/10.3847/2041-8213/adf320Globular star clustersCompact dwarf galaxiesN-body simulationsDark matter |
| spellingShingle | Ali Rostami-Shirazi Hosein Haghi Akram Hasani Zonoozi Pavel Kroupa Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1 The Astrophysical Journal Letters Globular star clusters Compact dwarf galaxies N-body simulations Dark matter |
| title | Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1 |
| title_full | Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1 |
| title_fullStr | Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1 |
| title_full_unstemmed | Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1 |
| title_short | Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1 |
| title_sort | dark star clusters or ultrafaint dwarf galaxies revisiting uma3 u1 |
| topic | Globular star clusters Compact dwarf galaxies N-body simulations Dark matter |
| url | https://doi.org/10.3847/2041-8213/adf320 |
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