scholarly journals Populating the Black Hole Mass Gaps in Stellar Clusters: General Relations and Upper Limits

2021 ◽  
Vol 923 (1) ◽  
pp. 126
Author(s):  
Johan Samsing ◽  
Kenta Hotokezaka
Keyword(s):  
Black Holes ◽  
Globular Clusters ◽  
Compact Object ◽  
Compact Objects ◽  
Stellar Clusters ◽  
Lower Mass ◽  
Single Star ◽  
Mass Gap ◽  
Star Models ◽  
Binary Mergers

Abstract Theory and observations suggest that single-star evolution is not able to produce black holes with masses in the range 3–5M ⊙ and above ∼45M ⊙, referred to as the lower mass gap and the upper mass gap, respectively. However, it is possible to form black holes in these gaps through mergers of compact objects in, e.g., dense clusters. This implies that if binary mergers are observed in gravitational waves with at least one mass-gap object, then either clusters are effective in assembling binary mergers, or our single-star models have to be revised. Understanding how effective clusters are at populating both mass gaps have therefore major implications for both stellar and gravitational wave astrophysics. In this paper we present a systematic study of how efficient stellar clusters are at populating both mass gaps through in-cluster mergers. For this, we derive a set of closed form relations for describing the evolution of compact object binaries undergoing dynamical interactions and mergers inside their cluster. By considering both static and time-evolving populations, we find in particular that globular clusters are clearly inefficient at populating the lower mass gap in contrast to the upper mass gap. We further describe how these results relate to the characteristic mass, time, and length scales associated with the problem.

scholarly journals Cosmological black holes are not described by the Thakurta metric: LIGO-Virgo bounds on PBHs remain unchanged

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Gert Hütsi ◽  
Tomi Koivisto ◽  
Martti Raidal ◽  
Ville Vaskonen ◽  
Hardi Veermäe
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Compact Object ◽  
Compact Objects ◽  
Primordial Black Hole ◽  
Mass Growth ◽  
Black Hole Binaries ◽  
Physical Conditions ◽  
Accretion Physics

AbstractWe show that the physical conditions which induce the Thakurta metric, recently studied by Bœhm et al. in the context of time-dependent black hole masses, correspond to a single accreting compact object in the entire Universe filled with isotropic non-interacting dust. In such a case, accretion physics is not local but tied to the properties of the whole Universe. We show that radiation, primordial black holes or particle dark matter cannot produce the specific energy flux required for supporting the mass growth of the compact objects described by the Thakurta metric. In particular, this solution does not apply to black hole binaries. We conclude that compact dark matter candidates and their mass growth cannot be described by the Thakurta metric, and thus existing constraints on the primordial black hole abundance from the LIGO-Virgo and the CMB measurements remain valid.

scholarly journals Black hole, neutron star, and white dwarf merger rates in AGN discs

2020 ◽  
Vol 498 (3) ◽  
pp. 4088-4094 ◽  
Author(s):  
B McKernan ◽  
K E S Ford ◽  
R O’Shaughnessy
Keyword(s):  
Black Hole ◽  
Compact Object ◽  
Relative Number ◽  
Expected Number ◽  
Lower Mass ◽  
Strong Function ◽  
Mass Gap ◽  
Mass Segregation ◽  
The Hill ◽  
Mass Functions

ABSTRACT Advanced LIGO and Advanced Virgo are detecting a large number of binary stellar origin black hole (BH) mergers. A promising channel for accelerated BH merger lies in active galactic nucleus (AGN) discs of gas around supermasssive BHs. Here, we investigate the relative number of compact object (CO) mergers in AGN disc models, including BH, neutron stars (NS), and white dwarfs, via Monte Carlo simulations. We find the number of all merger types in the bulk disc grows ∝ t1/3 which is driven by the Hill sphere of the more massive merger component. Median mass ratios of NS–BH mergers in AGN discs are $\tilde{q}=0.07\pm 0.06(0.14\pm 0.07)$ for mass functions (MF) M−1(− 2). If a fraction fAGN of the observed rate of BH–BH mergers (RBH–BH) come from AGN, the rate of NS–BH (NS–NS) mergers in the AGN channel is ${R}_{\mathrm{ BH}\!-\!\mathrm{ NS}} \sim f_{\mathrm{ AGN}}[10,300]\, \rm {Gpc}^{-3}\, \rm {yr}^{-1},({\mathit{ R}}_{NS\!-\!NS} \le \mathit{ f}_{AGN}400\, \rm {Gpc}^{-3}\, \rm {yr}^{-1}$). Given the ratio of NS–NS/BH–BH LIGO search volumes, from preliminary O3 results the AGN channel is not the dominant contribution to observed NS–NS mergers. The number of lower mass gap events expected is a strong function of the nuclear MF and mass segregation efficiency. CO merger ratios derived from LIGO can restrict models of MF, mass segregation, and populations embedded in AGN discs. The expected number of electromagnetic (EM) counterparts to NS–BH mergers in AGN discs at z < 1 is $\sim [30,900]\, {\rm {yr}}^{-1}(f_{\mathrm{ AGN}}/0.1)$. EM searches for flaring events in large AGN surveys will complement LIGO constraints on AGN models and the embedded populations that must live in them.

scholarly journals Accretion onto Relativistic Objects

1974 ◽  
Vol 64 ◽  
pp. 194-212
Author(s):  
M. J. Rees
Keyword(s):  
Black Holes ◽  
Interstellar Medium ◽  
Neutron Stars ◽  
Binary Systems ◽  
Compact Object ◽  
Stellar Mass ◽  
Supermassive Black Holes ◽  
Compact Objects ◽  
X Ray ◽  
Intergalactic Space

The physics of spherically symmetrical accretion onto a compact object is briefly reviewed. Neither neutron stars nor stellar-mass black holes are likely to be readily detectable if they are isolated and accreting from the interstellar medium. Supermassive black holes in intergalactic space may however be detectable. The effects of accretion onto compact objects in binary systems are then discussed, with reference to the phenomena observed in variable X-ray sources.

scholarly journals Effect of Compact Objects Near Be Stars

1987 ◽  
Vol 92 ◽  
pp. 516-518
Author(s):  
Krishna M.V. Apparao ◽  
S.P. Tarafdar
Keyword(s):  
Black Holes ◽  
Neutron Star ◽  
Rotation Period ◽  
Compact Object ◽  
Compact Objects ◽  
X Rays ◽  
Be Stars ◽  
Eccentric Orbit ◽  
X Ray ◽  
Be Star

Several Be stars are identified with bright X-ray sources. (Rappaport and Van den Heuvel, 1982). The bright X-ray emission and observed periodicities indicate the existence of compact objects (white dwarfs, neutron stars or black holes) near the Be stars. A prime example is the brightest X-ray source A0538-66 in LMC, which contains a neutron star with a rotation period of 59 ms. Apparao (1985) explained the X-ray emission, which occurs in periodic flares, by considering an inclined eccentric orbit for the neutron star around the assumed Be-star. The neutron star when it enters a gas ring (around the Be-star) accreting matter giving out X-rays.The X-ray emission from the compact objects, when the gas ring from the Be-star envelopes the objects, has interesting consequences. The X-ray emission produces an ionized region (compact object Stromgren sphere or COSS) in the gas surrounding the compact object (CO).

scholarly journals Further evidence for the non-existence of a unified hoop conjecture

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
Shahar Hod
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Critical Mass ◽  
Compact Object ◽  
Compact Objects ◽  
Necessary Condition ◽  
Adm Mass ◽  
Black Hole Spacetimes ◽  
Opposite Inequality ◽  
Hoop Conjecture

AbstractThe hoop conjecture, introduced by Thorne almost five decades ago, asserts that black holes are characterized by the mass-to-circumference relation $$4\pi {\mathcal {M}}/{\mathcal {C}}\ge 1$$ 4 π M / C ≥ 1 , whereas horizonless compact objects are characterized by the opposite inequality $$4\pi {\mathcal {M}}/{\mathcal {C}}<1$$ 4 π M / C < 1 (here $${\mathcal {C}}$$ C is the circumference of the smallest ring that can engulf the self-gravitating compact object in all azimuthal directions). It has recently been proved that a necessary condition for the validity of this conjecture in horizonless spacetimes of spatially regular charged compact objects is that the mass $${\mathcal {M}}$$ M be interpreted as the mass contained within the engulfing sphere (and not as the asymptotically measured total ADM mass). In the present paper we raise the following physically intriguing question: is it possible to formulate a unified version of the hoop conjecture which is valid for both black holes and horizonless compact objects? In order to address this important question, we analyze the behavior of the mass-to-circumference ratio of Kerr–Newman black holes. We explicitly prove that if the mass $${\mathcal {M}}$$ M in the hoop relation is interpreted as the quasilocal Einstein–Landau–Lifshitz–Papapetrou and Weinberg mass contained within the black-hole horizon, then these charged and spinning black holes are characterized by the sub-critical mass-to-circumference ratio $$4\pi {\mathcal {M}}/{\mathcal {C}}<1$$ 4 π M / C < 1 . Our results provide evidence for the non-existence of a unified version of the hoop conjecture which is valid for both black-hole spacetimes and spatially regular horizonless compact objects.

scholarly journals Black hole and neutron star mergers in galactic nuclei

2019 ◽  
Vol 488 (1) ◽  
pp. 47-63 ◽  
Author(s):  
Giacomo Fragione ◽  
Evgeni Grishin ◽  
Nathan W C Leigh ◽  
Hagai B Perets ◽  
Rosalba Perna
Keyword(s):  
Black Holes ◽  
Semimajor Axis ◽  
Galactic Nuclei ◽  
Mass Function ◽  
Compact Objects ◽  
Star Formation History ◽  
Large Numbers ◽  
Formation History ◽  
Binary Mergers ◽  
First Time

Abstract Nuclear star clusters surrounding supermassive black holes (SMBHs) in galactic nuclei contain large numbers of stars, black holes (BHs), and neutron stars (NSs), a fraction of which are likely to form binaries. These binaries were suggested to form a triple system with the SMBH, which acts as a perturber and may enhance BH and NS mergers via the Lidov–Kozai mechanism. We follow-up previous studies, but for the first time perform an extensive statistical study of BH–BH, NS–NS, and BH–NS binary mergers by means of direct high-precision regularized N-body simulations, including post-Newtonian (PN) terms up to order PN2.5. We consider different SMBH masses, slopes for the BH mass function, binary semimajor axis and eccentricity distributions, and different spatial distributions for the binaries. We find that the merger rates are a decreasing function of the SMBH mass and are in the ranges ∼0.17–0.52, ∼0.06–0.10, and ∼0.04–0.16 Gpc−3 yr−1 for BH–BH, BH–NS, and NS–NS binaries, respectively. However, the rate estimate from this channel remains highly uncertain and depends on the specific assumptions regarding the star formation history in galactic nuclei and the supply rate of compact objects (COs). We find that ${\sim } 10\!-\!20{{\ \rm per\ cent}}$ of the mergers enter the LIGO band with eccentricities ≳0.1. We also compare our results to the secular approximation, and show that N-body simulations generally predict a larger number of mergers. Finally, these events can also be observable via their electromagnetic counterparts, thus making these CO mergers especially valuable for cosmological and astrophysical purposes.

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 Evolution of binaries with compact objects in globular clusters

2014 ◽  
Vol 10 (S312) ◽  
pp. 203-212
Author(s):  
Natalia Ivanova
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Stars ◽  
Globular Clusters ◽  
Compact Objects ◽  
Stellar Systems ◽  
Stellar Objects ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

AbstractDynamical interactions that take place between objects in dense stellar systems lead to frequent formation of exotic stellar objects, unusual binaries, and systems of higher multiplicity. They are most important for the formation of binaries with neutron stars and black holes, which are usually observationally revealed in mass-transferring binaries. Here we review the current understanding of compact object's retention, of the metallicity dependence on the formation of low-mass X-ray binaries with neutron stars, and how mass-transferring binaries with a black hole and a white dwarf can be formed. We discuss as well one old unsolved puzzle and two new puzzles posed by recent observations: what descendants do ultra-compact X-ray binaries produce, how are very compact triples formed, and how can black hole low-mass X-ray binaries acquire non-degenerate companions?

scholarly journals Image of the thin accretion disk around compact objects in the Einstein–Gauss–Bonnet gravity

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
Galin Gyulchev ◽  
Petya Nedkova ◽  
Tsvetan Vetsov ◽  
Stoytcho Yazadjiev
Keyword(s):  
Black Holes ◽  
Accretion Disk ◽  
Physical Mechanism ◽  
Compact Object ◽  
Ring Structure ◽  
Compact Objects ◽  
Schwarzschild Black Hole ◽  
Naked Singularities ◽  
Bonnet Gravity ◽  
Light Ring

AbstractWe study the optical appearance of a thin accretion disk around compact objects within the Einstein–Gauss–Bonnet gravity. Considering static spherically symmetric black holes and naked singularities we search for characteristic signatures which can arise in the observable images due to the modification of general relativity. While the images of the Gauss–Bonnet black holes closely resemble the Schwarzschild black hole, naked singularities possess a distinctive feature. A series of bright rings are formed in the central part of the images with observable radiation $$10^3$$ 10 3 times larger than the rest of the flux making them observationally significant. We elucidate the physical mechanism, which causes the appearance of the central rings, showing that the image is determined by the light ring structure of the spacetime. In a certain region of the parametric space the Gauss–Bonnet naked singularities possess a stable and an unstable light ring. In addition the gravitational field becomes repulsive in a certain neighbourhood of the singularity. This combination of features leads to the formation of the central rings implying that the effect is not specific for the Einstein–Gauss–Bonnet gravity but would also appear for any other compact object with the same characteristics of the photon dynamics.

scholarly journals Modeling the outcome of supernova explosions in binary population synthesis using the stellar compactness

2021 ◽  
Author(s):  
Maciej Dabrowny ◽  
Nicola Giacobbo ◽  
Davide Gerosa
Keyword(s):  
Black Holes ◽  
Neutron Stars ◽  
Binary Stars ◽  
Compact Objects ◽  
Population Synthesis ◽  
Subsequent Formation ◽  
Compact Binaries ◽  
Mass Gap ◽  
Supernova Explosions

AbstractFollowing the collapse of their cores, some of the massive binary stars that populate our Universe are expected to form merging binaries composed of black holes and neutron stars. Gravitational-wave observations of the resulting compact binaries can reveal precious details on the inner workings of the supernova mechanism and the subsequent formation of compact objects. Within the framework of the population-synthesis code mobse, we present the implementation of a new supernova model that relies on the compactness of the collapsing star. The model has two free parameters, namely the compactness threshold that separates the formation of black holes and that of neutron stars, and the fraction of the envelope that falls back onto the newly formed black holes. We compare this model extensively against other prescriptions that are commonly used in binary population synthesis. We find that the cleanest signatures of the role of the pre-supernova stellar compactness are (1) the relative formation rates of the different kinds of compact binaries, which mainly depend on the compactness threshold parameter, and (2) the location of the upper edge of the mass gap between the lightest black holes and the heaviest neutron stars, which mainly depends on the fallback fraction.

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