Dark Star Clusters or Ultra-Faint Dwarf galaxies? Revisiting UMa3/U1
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arXiv
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| Autori principali: | , , , |
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| Natura: | Preprint |
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2025
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| author | Rostami-Shirazi, Ali Haghi, Hosein Zonoozi, Akram Hasani Kroupa, Pavel |
| author_facet | Rostami-Shirazi, Ali Haghi, Hosein Zonoozi, Akram Hasani Kroupa, Pavel |
| contents | 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 super-virial 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_sun/L_sun. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_10543 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Dark Star Clusters or Ultra-Faint Dwarf galaxies? Revisiting UMa3/U1 Rostami-Shirazi, Ali Haghi, Hosein Zonoozi, Akram Hasani Kroupa, Pavel Astrophysics of Galaxies 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 super-virial 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_sun/L_sun. |
| title | Dark Star Clusters or Ultra-Faint Dwarf galaxies? Revisiting UMa3/U1 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2508.10543 |