Evidence of star cluster migration and merger in dwarf galaxies
Poulain, Mélina; Smith, Rory; Duc, Pierre-Alain; Marleau, Francine R.; Habas, Rebecca; Durrell, Patrick R.; Fensch, Jérémy; Lim, Sungsoon; Müller, Oliver; Paudel, Sanjaya; Sánchez-Janssen, Rubén (2025-04-09)
Springer Nature
09.04.2025
Poulain, M., Smith, R., Duc, PA. et al. Evidence of star cluster migration and merger in dwarf galaxies. Nature 640, 902–906 (2025). https://doi.org/10.1038/s41586-025-08783-9.
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© The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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© The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:oulu-202504112527
https://urn.fi/URN:NBN:fi:oulu-202504112527
Tiivistelmä
Abstract
Nuclear star clusters (NSCs) are the densest stellar systems in the Universe. These clusters can be found at the centre of all galaxy types but tend to favour galaxies of intermediate stellar mass around 109\(M_⊙\) (refs.\(^{1,2}\)). At present, two main processes are under debate to explain their formation: in situ star formation from gas infall\(^3\) and migration and merging of globular clusters (GCs) caused by dynamical friction\(^4\). Studies\(^{5,6,7,8,9}\) of NSC stellar populations suggest that the former predominates in massive galaxies, whereas the latter prevails in dwarf galaxies, and both contribute equally at intermediate mass. However, until now, no ongoing merger of GCs has been observed to confirm this scenario. Here we report the serendipitous discovery of five dwarf galaxies with complex nuclear regions, characterized by multiple nuclei and tidal tails, using high-resolution images from the Hubble Space Telescope. These structures have been reproduced in complementary \(N\)-body simulations, supporting the interpretation that they result from migrating and merging of star clusters. The small detection rate and short simulated timescales (below 100 Myr) of this process may explain why this has not been observed previously. This study highlights the need for large surveys with high resolution to fully map the migration scenario steps.
Nuclear star clusters (NSCs) are the densest stellar systems in the Universe. These clusters can be found at the centre of all galaxy types but tend to favour galaxies of intermediate stellar mass around 109\(M_⊙\) (refs.\(^{1,2}\)). At present, two main processes are under debate to explain their formation: in situ star formation from gas infall\(^3\) and migration and merging of globular clusters (GCs) caused by dynamical friction\(^4\). Studies\(^{5,6,7,8,9}\) of NSC stellar populations suggest that the former predominates in massive galaxies, whereas the latter prevails in dwarf galaxies, and both contribute equally at intermediate mass. However, until now, no ongoing merger of GCs has been observed to confirm this scenario. Here we report the serendipitous discovery of five dwarf galaxies with complex nuclear regions, characterized by multiple nuclei and tidal tails, using high-resolution images from the Hubble Space Telescope. These structures have been reproduced in complementary \(N\)-body simulations, supporting the interpretation that they result from migrating and merging of star clusters. The small detection rate and short simulated timescales (below 100 Myr) of this process may explain why this has not been observed previously. This study highlights the need for large surveys with high resolution to fully map the migration scenario steps.
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