Journal article
Massive star cluster formation: II. Runaway stars as fossils of subcluster mergers
Astronomy and astrophysics (Berlin), v 690, 207
01 Oct 2024
Abstract
Two main mechanisms have classically been proposed for the formation of runaway stars. In the binary supernova scenario (BSS), a massive star in a binary explodes as a supernova, ejecting its companion. In the dynamical ejection scenario, a star is ejected during a strong dynamical encounter between multiple stars. We propose a third mechanism for the formation of runaway stars: the subcluster ejection scenario (SCES), where a subset of stars from an infalling subcluster is ejected out of the cluster via a tidal interaction with the contracting gravitational potential of the assembling cluster. We demonstrate the SCES in a star-by-star simulation of the formation of a young massive cluster from a 10(6) M-circle dot gas cloud using the TORCH framework. This star cluster forms hierarchically through a sequence of subcluster mergers determined by the initial turbulent, spherical conditions of the gas. We find that these mergers drive the formation of runaway stars in our model. Late-forming subclusters fall into the central potential, where they are tidally disrupted, forming tidal tails of runaway stars that are distributed highly anisotropically. Runaways formed in the same SCES have similar ages, velocities, and ejection directions. Surveying observations, we identify several SCES candidate groups with anisotropic ejection directions. The SCES is capable of producing runaway binaries: two wide dynamical binaries in infalling subclusters were tightened through ejection. This allows for another velocity kick via subsequent via a subsequent BSS ejection. An SCES-BSS ejection is a possible avenue for the creation of hypervelocity stars unbound to the Galaxy. The SCES occurs when subcluster formation is resolved. We expect nonspherical initial gas distributions to increase the number of calculated runaway stars, bringing it closer to observed values. The observation of groups of runaway stars formed via the SCES can thus reveal the assembly history of their natal clusters.
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Details
- Title
- Massive star cluster formation: II. Runaway stars as fossils of subcluster mergers
- Creators
- Brooke Polak - American Museum of Natural HistoryMordecai-Mark Mac Low - Amer Museum Nat Hist, Dept Astrophys, New York, NY 10024 USARalf S. Klessen - Heidelberg UniversitySimon Portegies Zwart - Leiden UniversityEric P. Andersson - American Museum of Natural HistorySabrina M. Appel - Rutgers, The State University of New JerseyClaude Cournoyer-Cloutier - McMaster UniversitySimon C. O. Glover - Heidelberg UniversityStephen L. W. Mcmillan - Drexel University
- Publication Details
- Astronomy and astrophysics (Berlin), v 690, 207
- Publisher
- Edp Sciences S A
- Number of pages
- 11
- Grant note
- PHY220160 / Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program 855130 / European Research Council via the ERC Synergy 15220; 2023/ENW/01498863 / Dutch National Supercomputing Center SURF Canada Graduate Scholarship - Doctoral (CGS D) from the Natural Sciences and Engineering Research Council of Canada (NSERC); Natural Sciences and Engineering Research Council of Canada (NSERC) INST 35/1134-1 FUGG; INST 35/1314-1 FUGG / German Science Foundation (DFG); German Research Foundation (DFG) AST18-15461; AST23-07950; AST-2009679 / NSF; National Science Foundation (NSF) Paris-Saclay University's Institut Pascal 21-38259; 21-38286; 21-38307; 21-37603; 21-38296 / National Science Foundation; National Science Foundation (NSF) 50OO2206 / German Ministry for Economic Affairs and Climate Action in project "MAINN" 80NSSC24K0935 / NASA Astrophysical Theory
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Physics
- Web of Science ID
- WOS:001331676100016
- Scopus ID
- 2-s2.0-85206810573
- Other Identifier
- 991022202092804721