Abbas Askar

Abbas Askar

Lunds Universitet

H-index: 24

Europe-Sweden

About Abbas Askar

Abbas Askar, With an exceptional h-index of 24 and a recent h-index of 22 (since 2020), a distinguished researcher at Lunds Universitet, specializes in the field of stellar dynamics, globular clusters, black holes, binary stars, gravitational waves.

His recent articles reflect a diverse array of research interests and contributions to the field:

New Parameters for Star Cluster Dynamics: the role of clusters initial conditions

Interpretable machine learning for finding intermediate-mass black holes

Astrophysics with the laser interferometer space antenna

Intermediate-Mass Black Holes in Star Clusters and Dwarf Galaxies

MOCCA-Survey Database: extra galactic globular clusters–III. The population of black holes in Milky Way and Andromeda-like galaxies

MOCCA-survey data base: extra galactic globular clusters–II. Milky Way and Andromeda

Preparing the next gravitational million-body simulations: evolution of single and binary stars in nbody6++gpu, mocca, and mcluster

MOCCA survey database I. BHs in star clusters

Abbas Askar Information

University

Lunds Universitet

Position

Postdoctoral Researcher

Citations(all)

3362

Citations(since 2020)

3037

Cited By

1582

hIndex(all)

24

hIndex(since 2020)

22

i10Index(all)

36

i10Index(since 2020)

34

Email

University Profile Page

Lunds Universitet

Abbas Askar Skills & Research Interests

stellar dynamics

globular clusters

black holes

binary stars

gravitational waves

Top articles of Abbas Askar

New Parameters for Star Cluster Dynamics: the role of clusters initial conditions

Authors

Bhavana Bhat,Barbara Lanzoni,Enrico Vesperini,Francesco R Ferraro,Francisco I Aros,Abbas Askar,Arkadiusz Hypki

Journal

arXiv preprint arXiv:2404.06992

Published Date

2024/4/10

We recently introduced three new parameters that describe the shape of the normalized cumulative radial distribution (nCRD) of the innermost stars in globular clusters and trace the clusters dynamical evolution. Here we extend our previous investigations to the case of a large set of Monte Carlo simulations of globular clusters, started from a broad range of initial conditions. All the models are analyzed at the same age of 13 Gyr, when they have reached different evolutionary phases. The sample of models is well representative of the structural properties of the observed population of Galactic globular clusters. We confirm that the three nCRD parameters are powerful tools to distinguish systems in early stages of dynamical evolution, from those that already experienced core collapse. They might also help disentangle clusters hosting a low-mass intermediate-mass black hole of a few hundred solar masses, from cases with large concentrations of dark remnants in their centers. With respect to other dynamical indicators, the nCRD parameters offer the advantage of being fully empirical and easier to measure from observational data.

Interpretable machine learning for finding intermediate-mass black holes

Authors

Mario Pasquato,Piero Trevisan,Abbas Askar,Pablo Lemos,Gaia Carenini,Michela Mapelli,Yashar Hezaveh

Journal

The Astrophysical Journal

Published Date

2024/4/9

Definitive evidence that globular clusters (GCs) host intermediate-mass black holes (IMBHs) is elusive. Machine-learning (ML) models trained on GC simulations can in principle predict IMBH host candidates based on observable features. This approach has two limitations: first, an accurate ML model is expected to be a black box due to complexity; second, despite our efforts to simulate GCs realistically, the simulation physics or initial conditions may fail to reflect reality fully. Therefore our training data may be biased, leading to a failure in generalization to observational data. Both the first issue—explainability/interpretability—and the second—out of distribution generalization and fairness—are active areas of research in ML. Here we employ techniques from these fields to address them: we use the anchors method to explain an Extreme Gradient Boosting (XGBoost) classifier; we also independently train a natively …

Astrophysics with the laser interferometer space antenna

Authors

Pau Amaro-Seoane,Jeff Andrews,Manuel Arca Sedda,Abbas Askar,Quentin Baghi,Razvan Balasov,Imre Bartos,Simone S Bavera,Jillian Bellovary,Christopher PL Berry,Emanuele Berti,Stefano Bianchi,Laura Blecha,Stéphane Blondin,Tamara Bogdanović,Samuel Boissier,Matteo Bonetti,Silvia Bonoli,Elisa Bortolas,Katelyn Breivik,Pedro R Capelo,Laurentiu Caramete,Federico Cattorini,Maria Charisi,Sylvain Chaty,Xian Chen,Martyna Chruślińska,Alvin JK Chua,Ross Church,Monica Colpi,Daniel D’orazio,Camilla Danielski,Melvyn B Davies,Pratika Dayal,Alessandra De Rosa,Andrea Derdzinski,Kyriakos Destounis,Massimo Dotti,Ioana Duţan,Irina Dvorkin,Gaia Fabj,Thierry Foglizzo,Saavik Ford,Jean-Baptiste Fouvry,Alessia Franchini,Tassos Fragos,Chris Fryer,Massimo Gaspari,Davide Gerosa,Luca Graziani,Paul Groot,Melanie Habouzit,Daryl Haggard,Zoltan Haiman,Wen-Biao Han,Alina Istrate,Peter H Johansson,Fazeel Mahmood Khan,Tomas Kimpson,Kostas Kokkotas,Albert Kong,Valeriya Korol,Kyle Kremer,Thomas Kupfer,Astrid Lamberts,Shane Larson,Mike Lau,Dongliang Liu,Nicole Lloyd-Ronning,Giuseppe Lodato,Alessandro Lupi,Chung-Pei Ma,Tomas Maccarone,Ilya Mandel,Alberto Mangiagli,Michela Mapelli,Stéphane Mathis,Lucio Mayer,Sean McGee,Berry McKernan,M Coleman Miller,David F Mota,Matthew Mumpower,Syeda S Nasim,Gijs Nelemans,Scott Noble,Fabio Pacucci,Francesca Panessa,Vasileios Paschalidis,Hugo Pfister,Delphine Porquet,John Quenby,Angelo Ricarte,Friedrich K Röpke,John Regan,Stephan Rosswog,Ashley Ruiter,Milton Ruiz,Jessie Runnoe,Raffaella Schneider,Jeremy Schnittman,Amy Secunda,Alberto Sesana,Naoki Seto,Lijing Shao,Stuart Shapiro,Carlos Sopuerta,Nicholas C Stone,Arthur Suvorov,Nicola Tamanini,Tomas Tamfal,Thomas Tauris,Karel Temmink,John Tomsick,Silvia Toonen,Alejandro Torres-Orjuela,Martina Toscani,Antonios Tsokaros,Caner Unal,Verónica Vázquez-Aceves,Rosa Valiante,Maurice van Putten,Jan van Roestel,Christian Vignali,Marta Volonteri,Kinwah Wu,Ziri Younsi,Shenghua Yu,Silvia Zane,Lorenz Zwick,Fabio Antonini,Vishal Baibhav,Enrico Barausse,Alexander Bonilla Rivera,Marica Branchesi,Graziella Branduardi-Raymont,Kevin Burdge,Srija Chakraborty,Jorge Cuadra,Kristen Dage,Benjamin Davis,Selma E de Mink,Roberto Decarli,Daniela Doneva,Stephanie Escoffier,Poshak Gandhi,Francesco Haardt,Carlos O Lousto,Samaya Nissanke,Jason Nordhaus

Published Date

2023/3/14

The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio …

Intermediate-Mass Black Holes in Star Clusters and Dwarf Galaxies

Authors

Abbas Askar,Vivienne F Baldassare,Mar Mezcua

Journal

arXiv preprint arXiv:2311.12118

Published Date

2023/11/20

Black holes with masses between 100 to 100,000 times the mass of the Sun are classified as intermediate-mass black holes, the possible missing link between stellar-mass and supermassive black holes. Stellar-mass black holes are endpoints of the evolution of stars initially more massive than roughly 20 and generally weigh about 10 to 100 . Supermassive black holes are found in the centre of many galaxies and weigh between to . The origin of supermassive black holes remains an unresolved problem in astrophysics, with many viable pathways suggesting that they undergo an intermediate-mass phase. Whether intermediate-mass black holes really stand as an independent category of black holes or rather they represent the heaviest stellar mass and the lightest supermassive black holes is still unclear, mostly owing to the lack of an observational smoking gun. The first part of this chapter summarises proposed formation channels of intermediate-mass black holes by focusing on their formation and growth in dense stellar environments like globular and nuclear star clusters. Also, it highlights how the growth of intermediate-mass black holes through mergers with other black holes is important from the point of view of gravitational waves and seeding of supermassive black holes in our Universe. The second part of the chapter focuses on the multi-wavelength observational constraints on intermediate-mass black holes in dense star clusters and dwarf galactic nuclei and the possible aid that future GW detectors can bring to unravel the mystery of intermediate-mass black holes.

MOCCA-Survey Database: extra galactic globular clusters–III. The population of black holes in Milky Way and Andromeda-like galaxies

Authors

A Leveque,M Giersz,Abbas Askar,M Arca-Sedda,A Olejak

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2023/4

This work investigates the black hole (BH) population of globular clusters (GCs) in Milky Way- and Andromeda-like galaxies. We combine the population synthesis code MASinGa and the MOCCA-Survey Database I to infer the properties of GCs harbouring a stellar-mass BH subsystem (BHS), an intermediate-mass BH (IMBH), or neither of those. We find that the typical number of GCs with a BHS, an IMBH, or none become comparable in the galactic outskirts, whilst the inner galactic regions are dominated by GCs without a significant dark component. We retrieve the properties of binary BHs (BBHs) that have either merged in the last 3 Gyr or survived in their parent cluster until present-day. We find that around 80 per cent of the merging BBHs form due to dynamical interactions while the remaining originate from evolution of primordial binaries. The inferred merger rate for both in-cluster and ejected mergers is …

MOCCA-survey data base: extra galactic globular clusters–II. Milky Way and Andromeda

Authors

A Leveque,M Giersz,M Arca-Sedda,Abbas Askar

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2022/8

A comprehensive study of the co-evolution of globular cluster systems (GCS) in galaxies requires the ability to model both the large-scale dynamics (0.01–10 kpc) regulating their orbital evolution, and the small-scale dynamics (sub-pc – au) regulating the internal dynamics of each globular cluster (GC). In this work, we present a novel method that combine semi-analytic models of GCS with fully self-consistent Monte Carlo models to simultaneously evolve large GCSs. We use the population synthesis code MASinGa and the MOCCA-Survey Database I to create synthetic GC populations aimed at representing the observed features of GCs in the Milky Way (MW) and Andromeda (M31). Our procedure enables us to recover the spatial and mass distribution of GCs in such galaxies, and to constrain the amount of mass that GCs left either in the halo as dispersed debris, or in the galactic centre, where they can …

Preparing the next gravitational million-body simulations: evolution of single and binary stars in nbody6++gpu, mocca, and mcluster

Authors

AWH Kamlah,A Leveque,R Spurzem,M Arca Sedda,A Askar,S Banerjee,P Berczik,M Giersz,J Hurley,D Belloni,L Kühmichel,L Wang

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2022/4

We present the implementation of updated stellar evolution recipes in the codes nbody6++gpu, mocca, and mcluster. We test them through numerical simulations of star clusters containing 1.1 × 105 stars (with 2.0 × 104 in primordial hard binaries) performing high-resolution direct N-body (nbody6++gpu) and Monte Carlo (mocca) simulations to an age of 10 Gyr. We compare models implementing either delayed or core-collapse supernovae mechanisms, a different mass ratio distribution for binaries, and white dwarf (WD) natal kicks enabled/disabled. Compared to nbody6++gpu, the mocca models appear to be denser, with a larger scatter in the remnant masses, and a lower binary fraction on average. The mocca models produce more black holes (BHs) and helium WDs, while nbody6++gpu models are characterized by a much larger amount of WD–WD binaries. The remnant kick velocity and escape speed …

MOCCA survey database I. BHs in star clusters

Authors

Mirek Giersz,Abbas Askar,Jakub Klencki,Jakub Morawski

Published Date

2022

We briefly describe and discuss the set-up of the project Mocca Survey Database I. The database contains more than 2000 Monte Carlo models of evolution of real star cluster performed with the Mocca code. Then, we very briefly discuss results of analysis of the database regarding the following projects: formation of intermediate mass black holes, abrupt cluster dissolution harboring black hole subsystems, retention fraction of black hole - black hole mergers, and tidal disruption events with intermediate mass black holes.

MOCCA-SURVEY data base II–Properties of intermediate mass black holes escaping from star clusters

Authors

Konrad Maliszewski,Mirek Giersz,Dorota Gondek-Rosinska,Abbas Askar,Arkadiusz Hypki

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2022/8

In this work, we investigate properties of intermediate-mass black holes (IMBHs) that escape from star clusters due to dynamical interactions. The studied models were simulated as part of the preliminary second survey carried out using the MOCCA code (MOCCA-SURVEY Database II), which is based on the Monte Carlo N-body method and does not include gravitational wave recoil kick prescriptions of the binary black hole merger product. We have found that IMBHs are more likely to be formed and ejected in models where both initial central density and central escape velocities have high values. Most of our studied objects escape in a binary with another black hole (BH) as their companion and have masses between 100 and . Escaping IMBHs tend to build-up mass most effectively through repeated mergers in a binary with BHs due to gravitational wave emission. Binaries play a key role in their …

mocca: dynamics and evolution of single and binary stars of multiple stellar populations in tidally filling and underfilling globular star clusters

Authors

Arkadiusz Hypki,Mirek Giersz,Jongsuk Hong,Agostino Leveque,Abbas Askar,Diogo Belloni,Magdalena Otulakowska-Hypka

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2022/12

We present an upgraded version of the mocca code for the study of dynamical evolution of globular clusters (GCs) and its first application to the study of evolution of multiple stellar populations. We explore initial conditions spanning different structural parameters for the first (FG) and second generation of stars (SG) and we analyse their effect on the binary dynamics and survival. Here, we focus on the number ratio of FG and SG binaries, their spatial variation, and the way their abundances are affected by various cluster initial properties. We find that present-day SG stars are more abundant in clusters that were initially tidally filling. Conversely, FG stars stay more abundant in clusters that were initially tidally underfilling. We find that the ratio between binary fractions is not affected by the way we calculate these fractions [e.g. only main-sequence binaries (MS) or observational binaries, i.e. MS stars >0.4 M⊙ mass …

MOCCA-survey data base

Authors

Agostino Leveque,Mirek Giersz,Manuel Arca Sedda,Abbas Askar

Published Date

2022/6/17

A comprehensive study of the co-evolution of globular cluster systems (GCS) in galaxies requires the ability to model both the large-scale dynamics (0.01-10 kpc) regulating their orbital evolution, and the small-scale dynamics (sub-pc-au) regulating the internal dynamics of each globular cluster (GC). In this work, we present a novel method that combine semi-analytic models of GCS with fully self-consistent Monte Carlo models to simultaneously evolve large GCSs. We use the population synthesis code MASinGa and the MOCCA-Survey Database I to create synthetic GC populations aimed at representing the observed features of GCs in the Milky Way (MW) and Andromeda (M31). Our procedure enables us to recover the spatial and mass distribution of GCs in such galaxies, and to constrain the amount of mass that GCs left either in the halo as dispersed debris, or in the galactic centre, where they can contribute to …

Influence of tidal dissipation on outcomes of binary–single encounters between stars and black holes in stellar clusters

Authors

Lucas Hellström,Abbas Askar,Alessandro A Trani,Mirek Giersz,Ross P Church,Johan Samsing

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2022/12

In the cores of dense stellar clusters, close gravitational encounters between binary and single stars can frequently occur. Using the tsunami code, we computed the outcome of a large number of binary–single interactions involving two black holes (BHs) and a star to check how the inclusion of orbital energy losses due to tidal dissipation can change the outcome of these chaotic interactions. Each interaction was first simulated without any dissipative processes and then we systematically added orbital energy losses due to gravitational wave emission [using post-Newtonian (PN) corrections] and dynamical tides and recomputed the interactions. We find that the inclusion of tides increases the number of BH–star mergers by up to 75 per cent; however, it does not affect the number of BH–BH mergers. These results highlight the importance of including orbital energy dissipation due to dynamical tides during few …

Dynamical formation of GW190521 in stellar clusters

Authors

Abbas Askar

Journal

APS April Meeting Abstracts

Published Date

2022/4

In 2020, the LIGO/Virgo Collaboration announced the discovery of GW190521 in which a 142 solar mass black hole (BH) formed from the merger of 85 solar mass and 66 solar mass BHs. This discovery provides the first concrete evidence for the existence of an intermediate-mass BH (IMBH) larger than a 100 solar mass. BHs with these masses had not been observed before and theoretical models show that they are difficult to form through isolated stellar/binary evolution of massive stars. Many stars are born in stellar clusters where the density of stars can be up to a million times higher than the density of stars in the solar neighbourhood (eg, globular clusters (GCs), nuclear stellar clusters (NSCs). Close gravitational encounters between binary stars and BHs are conducive to dynamically forming merging BBHs in these dense stellar environments. If the merged BH is retained in the cluster, then additional dynamical …

Exploring compact binary populations with the Einstein Telescope

Authors

Neha Singh,Tomasz Bulik,Krzysztof Belczynski,Abbas Askar

Journal

Astronomy & Astrophysics

Published Date

2022/11/1

The Einstein Telescope (ET), a wide-band, future third generation gravitational wave detector, is expected to have detection rates of ∼105 − 106 binary black hole (BBH) detections and ∼7 × 104 binary neutron star (BNS) detections in one year. The coalescence of compact binaries with a total mass of 20–100 M⊙, typical of BH-BH or BH-NS binaries, will be visible up to redshift z ≈ 20 and even higher, thus facilitating the understanding of the dark era of the Universe preceding the birth of the first stars. The ET will therefore be a crucial instrument for population studies. We analysed the compact binaries originating in stars from (i) Population (Pop) I+II, (ii) Pop III, and (iii) globular clusters (GCs), with the single ET instrument, using the ET-D design sensitivity for the analysis. We estimated the constraints on the chirp mass, redshift, and merger rate as function of redshift for these classes of compact object …

Formation of supermassive black holes in galactic nuclei–II. Retention and growth of seed intermediate-mass black holes

Authors

Abbas Askar,Melvyn B Davies,Ross P Church

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2022/4

In many galactic nuclei, a nuclear stellar cluster (NSC) co-exists with a supermassive black hole (SMBH). In this second one in a series of papers, we further explore the idea that the NSC forms before the SMBH through the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow by mergers and accretion to form an SMBH. To check the observable consequences of this proposed SMBH seeding mechanism, we created an observationally motivated mock population of galaxies, in which NSCs are constructed by aggregating stellar clusters that may or may not contain IMBHs. Based on several assumptions, we model the growth of IMBHs in the NSCs through gravitational wave (GW) mergers with other IMBHs and gas accretion. In the case of GW mergers, the merged BH can either be retained or ejected depending on the GW recoil kick it receives. The …

VizieR Online Data Catalog: Finding black holes with black boxes (Askar+, 2019)

Authors

A Askar,A Askar,M Pasquato,M Giersz

Journal

VizieR Online Data Catalog

Published Date

2022/10

For the purpose of this study, we used results from numerical simulations of GC models that were carried out using the MOCCA code (Hypki & Giersz 2013MNRAS. 429.1221 H; Giersz et al. 2013MNRAS. 429.1221 H) as part of the MOCCA-Survey Database I (Askar et al. 2017MNRAS. 464L.. 36A) project. MOCCA is a code for simulating star clusters based on Henon's implementation of the Monte Carlo method (Henon 1971Ap&SS.. 14.. 151H; Stodolkiewicz 1982AcA.... 32... 63S, 1986AcA.... 36... 19S) to follow the long-term dynamical evolution of spherically symmetric stellar clusters.

Using binaries in globular clusters to catch sight of intermediate-mass black holes

Authors

Francisco I Aros,Anna C Sippel,Alessandra Mastrobuono-Battisti,Paolo Bianchini,Abbas Askar,Glenn Van De Ven

Journal

Monthly Notices of the Royal Astronomical Society

Published Date

2021/12

The dynamical evolution of globular clusters (GCs) is tied to their binary population, as binaries segregate to the cluster centre, leading to an increased binary fraction in the core. This central overabundance of mainly hard binaries can serve as a source of energy for the cluster and has a significant effect on the observed kinematics, such as artificially increasing the observed line-of-sight velocity dispersion. We analyse the binary fractions and distributions of 95 simulated GCs, with and without an intermediate-mass black hole (IMBH) in their centre. We show that an IMBH will not only halt the segregation of binaries towards the cluster centre, but also, directly and indirectly, disrupt the binaries that segregate, thus, depleting binaries in the cluster core. We illustrate this by showing that clusters with an IMBH have fewer binaries and flatter radial binary distributions than their counterparts without one. These differences in …

A 4D flow cardiovascular magnetic resonance study of flow asymmetry and haemodynamic quantity correlations in the pulmonary artery

Authors

Henrike Gbinigie,Louise Coats,Jehill D Parikh,Kieren G Hollingsworth,Lian Gan

Journal

Physiological Measurement

Published Date

2021/3/5

Objective In this paper we elucidate the asymmetric flow pattern and the haemodynamic quantity distributions and correlations in the pulmonary artery (PA) vasculature in healthy adults having structurally normal hearts, to provide reference on the flow characteristics in the PA and the right ventricle. Approach Velocity data are acquired non-invasively from 18 healthy volunteers by 4D flow magnetic resonance imaging, resolved to 20 phases with spatial resolution 3× 3× 3 mm 3. Interpolation is applied to improve the accuracy in quantifying haemodynamic quantities including kinetic energy, rotational energy, helicity and energy dissipation rate. These quantities are volumetrically normalised to remove size dependency, representing densities or local intensity. Main results Flow asymmetry in the PA is quantified in terms of all the flow dynamic quantities and their correlations. The right PA has larger diameter and …

Single-single gravitational-wave captures in globular clusters: Eccentric deci-Hertz sources observable by DECIGO and Tian-Qin

Authors

Johan Samsing,Daniel J D’Orazio,Kyle Kremer,Carl L Rodriguez,Abbas Askar

Journal

Physical Review D

Published Date

2020/6/9

We study the formation rate of binary black hole mergers formed through gravitational-wave emission between unbound, single black holes in globular clusters. While the formation of these binaries in very dense systems such as galactic nuclei has been well studied, we show here that this process can operate in lower-density stellar systems as well, forming binaries at a rate similar to other proposed pathways for creating eccentric mergers. Recent advances in post-Newtonian cluster dynamics indicate that a large fraction of dynamically assembled binary black holes merge inside their host clusters during weak and strong binary-single and binary-binary interactions, and that these systems may retain measurable eccentricities as they travel through the LIGO and LISA sensitivity bands. Using an analytic approach to modeling binary black holes from globular clusters, we show that the formation of merging binaries …

Evolutionary roads leading to low effective spins, high black hole masses, and O1/O2 rates for LIGO/Virgo binary black holes

Authors

K Belczynski,J Klencki,CE Fields,A Olejak,E Berti,G Meynet,CL Fryer,DE Holz,R O’Shaughnessy,DA Brown,T Bulik,SC Leung,K Nomoto,P Madau,R Hirschi,E Kaiser,S Jones,S Mondal,M Chruslinska,P Drozda,D Gerosa,Z Doctor,M Giersz,S Ekstrom,C Georgy,A Askar,V Baibhav,D Wysocki,T Natan,WM Farr,G Wiktorowicz,M Coleman Miller,B Farr,J-P Lasota

Journal

Astronomy & Astrophysics

Published Date

2020/4/1

All ten LIGO/Virgo binary black hole (BH-BH) coalescences reported following the O1/O2 runs have near-zero effective spins. There are only three potential explanations for this. If the BH spin magnitudes are large, then: (i) either both BH spin vectors must be nearly in the orbital plane or (ii) the spin angular momenta of the BHs must be oppositely directed and similar in magnitude. Then there is also the possibility that (iii) the BH spin magnitudes are small. We consider the third hypothesis within the framework of the classical isolated binary evolution scenario of the BH-BH merger formation. We test three models of angular momentum transport in massive stars: a mildly efficient transport by meridional currents (as employed in the Geneva code), an efficient transport by the Tayler-Spruit magnetic dynamo (as implemented in the MESA code), and a very-efficient transport (as proposed by Fuller et al.) to calculate natal …

See List of Professors in Abbas Askar University(Lunds Universitet)

Abbas Askar FAQs

What is Abbas Askar's h-index at Lunds Universitet?

The h-index of Abbas Askar has been 22 since 2020 and 24 in total.

What are Abbas Askar's top articles?

The articles with the titles of

New Parameters for Star Cluster Dynamics: the role of clusters initial conditions

Interpretable machine learning for finding intermediate-mass black holes

Astrophysics with the laser interferometer space antenna

Intermediate-Mass Black Holes in Star Clusters and Dwarf Galaxies

MOCCA-Survey Database: extra galactic globular clusters–III. The population of black holes in Milky Way and Andromeda-like galaxies

MOCCA-survey data base: extra galactic globular clusters–II. Milky Way and Andromeda

Preparing the next gravitational million-body simulations: evolution of single and binary stars in nbody6++gpu, mocca, and mcluster

MOCCA survey database I. BHs in star clusters

...

are the top articles of Abbas Askar at Lunds Universitet.

What are Abbas Askar's research interests?

The research interests of Abbas Askar are: stellar dynamics, globular clusters, black holes, binary stars, gravitational waves

What is Abbas Askar's total number of citations?

Abbas Askar has 3,362 citations in total.

What are the co-authors of Abbas Askar?

The co-authors of Abbas Askar are M.B.N. Kouwenhoven, Johan Samsing, Magdalena Szkudlarek.

Co-Authors

H-index: 28
M.B.N. Kouwenhoven

M.B.N. Kouwenhoven

Xi'an Jiaotong-Liverpool University

H-index: 24
Johan Samsing

Johan Samsing

Princeton University

H-index: 4
Magdalena Szkudlarek

Magdalena Szkudlarek

Uniwersytet Zielonogórski

academic-engine