Pair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave Implications
The detection of the gravitational-wave (GW) event GW190521 raises questions about the formation of black holes (BHs) within the pair-instability mass gap (PIBHs). We propose that Population III star clusters significantly contribute to events similar to GW190521. We perform N -body simulations and...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/add1df |
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| author | Weiwei Wu Long Wang Shuai Liu Yining Sun Ataru Tanikawa Michiko Fujii |
| author_facet | Weiwei Wu Long Wang Shuai Liu Yining Sun Ataru Tanikawa Michiko Fujii |
| author_sort | Weiwei Wu |
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| description | The detection of the gravitational-wave (GW) event GW190521 raises questions about the formation of black holes (BHs) within the pair-instability mass gap (PIBHs). We propose that Population III star clusters significantly contribute to events similar to GW190521. We perform N -body simulations and find that PIBHs can form from stellar collisions or binary black hole (BBH) mergers, with the latter accounting for 90% of the contributions. Due to GW recoil during BBH mergers, approximately 10%–50% of PIBHs formed via BBH mergers that escaped from clusters, depending on BH spins and cluster escape velocities. The remaining PIBHs can participate in secondary and multiple BBH formation events, contributing to GW events. Assuming Population III stars form in massive clusters (initially 100,000 M _⊙ ) with a top-heavy initial mass function, the average merger rates for GW events involving PIBHs with 0% and 100% primordial binaries are 0.005 and 0.017 yr ^−1 Gpc ^−3 , respectively, with maximum values of 0.030 and 0.106 yr ^−1 Gpc ^−3 . If Population III stars form in low-mass clusters (initial mass of 1000 M _⊙ and 10,000 M _⊙ ), the merger rate is comparable with a 100% primordial binary fraction but significantly lower without primordial binaries. We also calculate the characteristic strains of the GW events in our simulations and find that about 43.4% (LISA), 97.8% (Taiji), and 66.4% (Tianqin) of these events could potentially be detected by space-borne detectors, including LISA, Taiji, and TianQin. Next-generation GW detectors such as DECIGO, the Einstein Telescope, and Cosmic Explorer can nearly cover all these signals. |
| format | Article |
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| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-511e754c88a249d0902562d9becf23d12025-08-20T03:45:24ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01986216310.3847/1538-4357/add1dfPair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave ImplicationsWeiwei Wu0Long Wang1https://orcid.org/0000-0001-8713-0366Shuai Liu2Yining Sun3Ataru Tanikawa4https://orcid.org/0000-0002-8461-5517Michiko Fujii5School of Physics and Astronomy, Sun Yat-sen University , Daxue Road, Zhuhai, 519082, People’s Republic of China ; wanglong8@sysu.edu.cnSchool of Physics and Astronomy, Sun Yat-sen University , Daxue Road, Zhuhai, 519082, People’s Republic of China ; wanglong8@sysu.edu.cn; CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area , Zhuhai, 519082, People’s Republic of ChinaSchool of Electronic and Electrical Engineering, Zhaoqing University , Zhaoqing 526061, People’s Republic of ChinaSchool of Physics and Astronomy, Sun Yat-sen University , Daxue Road, Zhuhai, 519082, People’s Republic of China ; wanglong8@sysu.edu.cnCenter for Information Science, Fukui Prefectural University , 4-1-1 Matsuoka Kenjojima, Eiheiji-cho, Fukui 910-1195, JapanDepartment of Astronomy, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JapanThe detection of the gravitational-wave (GW) event GW190521 raises questions about the formation of black holes (BHs) within the pair-instability mass gap (PIBHs). We propose that Population III star clusters significantly contribute to events similar to GW190521. We perform N -body simulations and find that PIBHs can form from stellar collisions or binary black hole (BBH) mergers, with the latter accounting for 90% of the contributions. Due to GW recoil during BBH mergers, approximately 10%–50% of PIBHs formed via BBH mergers that escaped from clusters, depending on BH spins and cluster escape velocities. The remaining PIBHs can participate in secondary and multiple BBH formation events, contributing to GW events. Assuming Population III stars form in massive clusters (initially 100,000 M _⊙ ) with a top-heavy initial mass function, the average merger rates for GW events involving PIBHs with 0% and 100% primordial binaries are 0.005 and 0.017 yr ^−1 Gpc ^−3 , respectively, with maximum values of 0.030 and 0.106 yr ^−1 Gpc ^−3 . If Population III stars form in low-mass clusters (initial mass of 1000 M _⊙ and 10,000 M _⊙ ), the merger rate is comparable with a 100% primordial binary fraction but significantly lower without primordial binaries. We also calculate the characteristic strains of the GW events in our simulations and find that about 43.4% (LISA), 97.8% (Taiji), and 66.4% (Tianqin) of these events could potentially be detected by space-borne detectors, including LISA, Taiji, and TianQin. Next-generation GW detectors such as DECIGO, the Einstein Telescope, and Cosmic Explorer can nearly cover all these signals.https://doi.org/10.3847/1538-4357/add1dfPopulation III starsN-body simulationsSupernova remnantsGravitational wave astronomy |
| spellingShingle | Weiwei Wu Long Wang Shuai Liu Yining Sun Ataru Tanikawa Michiko Fujii Pair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave Implications The Astrophysical Journal Population III stars N-body simulations Supernova remnants Gravitational wave astronomy |
| title | Pair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave Implications |
| title_full | Pair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave Implications |
| title_fullStr | Pair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave Implications |
| title_full_unstemmed | Pair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave Implications |
| title_short | Pair-instability Gap Black Holes in Population III Star Clusters: Pathways, Dynamics, and Gravitational-wave Implications |
| title_sort | pair instability gap black holes in population iii star clusters pathways dynamics and gravitational wave implications |
| topic | Population III stars N-body simulations Supernova remnants Gravitational wave astronomy |
| url | https://doi.org/10.3847/1538-4357/add1df |
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