scholarly journals Binary black holes in the pair instability mass gap

2020 ◽  
Vol 497 (1) ◽  
pp. 1043-1049 ◽  
Author(s):  
Ugo N Di Carlo ◽  
Michela Mapelli ◽  
Yann Bouffanais ◽  
Nicola Giacobbo ◽  
Filippo Santoliquido ◽  
...  
Keyword(s):  
Black Holes ◽  
Formation Rate ◽  
Star Clusters ◽  
Design Sensitivity ◽  
Young Star ◽  
Binary Black Holes ◽  
Single Star ◽  
Mass Gap ◽  
Young Star Clusters ◽  
Stellar Mergers

ABSTRACT Pair instability (PI) and pulsational PI prevent the formation of black holes (BHs) with mass ≳60 M⊙ from single star evolution. Here, we investigate the possibility that BHs with mass in the PI gap form via stellar mergers and multiple stellar mergers, facilitated by dynamical encounters in young star clusters. We analyse 104 simulations, run with the direct N-body code nbody6++gpu coupled with the population synthesis code mobse. We find that up to ∼6 per cent of all simulated BHs have mass in the PI gap, depending on progenitor’s metallicity. This formation channel is strongly suppressed in metal-rich (Z = 0.02) star clusters because of stellar winds. BHs with mass in the PI gap are initially single BHs but can efficiently acquire companions through dynamical exchanges. We find that ∼21 per cent, 10 per cent, and 0.5 per cent of all binary BHs have at least one component in the PI mass gap at metallicity Z = 0.0002, 0.002, and 0.02, respectively. Based on the evolution of the cosmic star formation rate and metallicity, and under the assumption that all stars form in young star clusters, we predict that ∼5 per cent of all binary BH mergers detectable by advanced LIGO and Virgo at their design sensitivity have at least one component in the PI mass gap.

scholarly journals Intermediate-mass black holes from stellar mergers in young star clusters

2021 ◽  
Vol 507 (4) ◽  
pp. 5132-5143
Author(s):  
Ugo N Di Carlo ◽  
Michela Mapelli ◽  
Mario Pasquato ◽  
Sara Rastello ◽  
Alessandro Ballone ◽  
...  
Keyword(s):  
Black Holes ◽  
Star Clusters ◽  
Mass Range ◽  
Young Star ◽  
Intermediate Mass ◽  
Stellar Collisions ◽  
Low Metallicity ◽  
Young Star Clusters ◽  
Stellar Mergers ◽  
Intermediate Mass Black Holes

ABSTRACT Intermediate-mass black holes (IMBHs) in the mass range $10^2\!-\!10^5\, \mathrm{M_{\odot }}$ bridge the gap between stellar black holes (BHs) and supermassive BHs. Here, we investigate the possibility that IMBHs form in young star clusters via runaway collisions and BH mergers. We analyse 104 simulations of dense young star clusters, featuring up-to-date stellar wind models and prescriptions for core collapse and (pulsational) pair instability. In our simulations, only nine IMBHs out of 218 form via binary BH mergers, with a mass ∼100–140 M⊙. This channel is strongly suppressed by the low escape velocity of our star clusters. In contrast, IMBHs with masses up to ∼438 M⊙ efficiently form via runaway stellar collisions, especially at low metallicity. Up to ∼0.2 per cent of all the simulated BHs are IMBHs, depending on progenitor’s metallicity. The runaway formation channel is strongly suppressed in metal-rich (Z = 0.02) star clusters, because of stellar winds. IMBHs are extremely efficient in pairing with other BHs: ∼70 per cent of them are members of a binary BH at the end of the simulations. However, we do not find any IMBH–BH merger. More massive star clusters are more efficient in forming IMBHs: ∼8 per cent (∼1 per cent) of the simulated clusters with initial mass 104–3 × 104 M⊙ (103–5 × 103 M⊙) host at least one IMBH.

scholarly journals Binary black holes in young star clusters: the impact of metallicity

2020 ◽  
Vol 498 (1) ◽  
pp. 495-506 ◽  
Author(s):  
Ugo N Di Carlo ◽  
Michela Mapelli ◽  
Nicola Giacobbo ◽  
Mario Spera ◽  
Yann Bouffanais ◽  
...  
Keyword(s):  
Black Holes ◽  
Initial Density ◽  
Star Clusters ◽  
Young Star ◽  
Binary Black Holes ◽  
Binary Evolution ◽  
Merger Rate ◽  
The Masses ◽  
The Impact ◽  
Young Star Clusters

ABSTRACT Young star clusters are the most common birthplace of massive stars and are dynamically active environments. Here, we study the formation of black holes (BHs) and binary black holes (BBHs) in young star clusters, by means of 6000 N-body simulations coupled with binary population synthesis. We probe three different stellar metallicities (Z = 0.02, 0.002, and 0.0002) and two initial-density regimes (density at the half-mass radius ρh ≥ 3.4 × 104 and ≥1.5 × 102 M⊙ pc−3 in dense and loose star clusters, respectively). Metal-poor clusters tend to form more massive BHs than metal-rich ones. We find ∼6, ∼2, and <1 per cent of BHs with mass mBH > 60 M⊙ at Z = 0.0002, 0.002, and 0.02, respectively. In metal-poor clusters, we form intermediate-mass BHs with mass up to ∼320 M⊙. BBH mergers born via dynamical exchanges (exchanged BBHs) can be more massive than BBH mergers formed from binary evolution: the former (latter) reach total mass up to ∼140 M⊙ (∼80 M⊙). The most massive BBH merger in our simulations has primary mass ∼88 M⊙, inside the pair-instability mass gap, and a mass ratio of ∼0.5. Only BBHs born in young star clusters from metal-poor progenitors can match the masses of GW 170729, the most massive event in first and second observing run (O1 and O2), and those of GW 190412, the first unequal-mass merger. We estimate a local BBH merger rate density ∼110 and ∼55 Gpc−3 yr−1, if we assume that all stars form in loose and dense star clusters, respectively.

scholarly journals Constraining the Fraction of Binary Black Holes Formed in Isolation and Young Star Clusters with Gravitational-wave Data

2019 ◽  
Vol 886 (1) ◽  
pp. 25 ◽  
Author(s):  
Yann Bouffanais ◽  
Michela Mapelli ◽  
Davide Gerosa ◽  
Ugo N. Di Carlo ◽  
Nicola Giacobbo ◽  
...  
Keyword(s):  
Black Holes ◽  
Gravitational Wave ◽  
Star Clusters ◽  
Young Star ◽  
Binary Black Holes ◽  
Wave Data ◽  
Young Star Clusters

scholarly journals Formation of nuclear rings of barred galaxies and star formation therein

2013 ◽  
Vol 9 (S303) ◽  
pp. 43-53 ◽  
Author(s):  
Woong-Tae Kim ◽  
Woo-Young Seo ◽  
Yonghwi Kim
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Star Clusters ◽  
Young Star ◽  
Centrifugal Barrier ◽  
Barred Galaxies ◽  
Contact Points ◽  
Nuclear Ring ◽  
Substructure Formation ◽  
Young Star Clusters

AbstractBarred galaxies contain substructures such as a pair of dust lanes and nuclear rings, with the latter being sites of intense star formation. We study the substructure formation as well as star formation in nuclear rings using numerical simulations. We find that nuclear rings form not by the Lindblad resonances, as previously thought, but by the centrifugal barrier that inflowing gas along dust lanes cannot overcome. This predicts a smaller ring in a more strongly barred galaxy, consistent with observations. Star formation rate (SFR) in a nuclear ring is determined primarily by the mass inflow rate to the ring. In our models, the SFR typically shows a short strong burst associated with the rapid gas infall and stays very small for the rest of the evolution. When the SFR is low, ages of young star clusters exhibit an azimuthal gradient along the ring since star formation takes place mostly near the contact points between the dust lanes and the nuclear ring. When the SFR is large, on the other hand, star formation is widely distributed throughout the whole length of the ring, with no apparent age gradient of star clusters. Since observed ring star formation appears long-lived with episodic bursts, our results suggest that the bar region should be replenished continually with fresh gas from outside.

scholarly journals Intermediate-mass Black Holes from High Massive-star Binary Fractions in Young Star Clusters

2021 ◽  
Vol 908 (2) ◽  
pp. L29 ◽  
Author(s):  
Elena González ◽  
Kyle Kremer ◽  
Sourav Chatterjee ◽  
Giacomo Fragione ◽  
Carl L. Rodriguez ◽  
...  
Keyword(s):  
Black Holes ◽  
Massive Star ◽  
Star Clusters ◽  
Young Star ◽  
Intermediate Mass ◽  
Star Binary ◽  
Young Star Clusters ◽  
Intermediate Mass Black Holes

scholarly journals GW190521 formation via three-body encounters in young massive star clusters

2021 ◽  
Author(s):  
Marco Dall’Amico ◽  
Michela Mapelli ◽  
Ugo N Di Carlo ◽  
Yann Bouffanais ◽  
Sara Rastello ◽  
...  
Keyword(s):  
Black Hole ◽  
First Generation ◽  
Massive Star ◽  
Second Generation ◽  
Star Clusters ◽  
Young Star ◽  
Mass Gap ◽  
Stellar Collisions ◽  
Three Body ◽  
Young Star Clusters

Abstract GW190521 is the most massive binary black hole (BBH) merger observed to date, and its primary component lies in the pair-instability (PI) mass gap. Here, we investigate the formation of GW190521-like systems via three-body encounters in young massive star clusters. We performed 2× 105 simulations of binary-single interactions between a BBH and a massive ≥60 M⊙ black hole (BH), including post-Newtonian terms up to the 2.5 order and a prescription for relativistic kicks. In our initial conditions, we take into account the possibility of forming BHs in the PI mass gap via stellar collisions. If we assume that first-generation BHs have low spins, $\sim {0.17}{{\ \rm per\ cent}}$ of all the simulated BBH mergers have component masses, effective and precessing spin, and remnant mass and spin inside the $90{{\ \rm per\ cent}}$ credible intervals of GW190521. Seven of these systems are first-generation exchanged binaries, while five are second-generation BBHs. We estimate a merger rate density $\mathcal {R}_{\rm GW190521}\sim {0.03}\,$Gpc−3 yr−1 for GW190521-like binaries formed via binary-single interactions in young star clusters. This rate is extremely sensitive to the spin distribution of first-generation BBHs. Stellar collisions, second-generation mergers and dynamical exchanges are the key ingredients to produce GW190521-like systems in young star clusters.

scholarly journals Merging black holes in young star clusters

2019 ◽  
Vol 487 (2) ◽  
pp. 2947-2960 ◽  
Author(s):  
Ugo N Di Carlo ◽  
Nicola Giacobbo ◽  
Michela Mapelli ◽  
Mario Pasquato ◽  
Mario Spera ◽  
...  
Keyword(s):  
Black Holes ◽  
Star Clusters ◽  
Young Star ◽  
Young Star Clusters
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