Compact Object Modeling in the Globular Cluster 47 Tucanae

Ye, Claire S.; Kremer, Kyle; Rodriguez, Carl L.; Rui, Nicholas Z.; Weatherford, Newlin C.; Chatterjee, Sourav; Fragione, Giacomo; Rasio, Frederic A.

doi:10.48550/arxiv.2110.05495

Cited by 4 publications

(11 citation statements)

References 108 publications

(177 reference statements)

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“…These clusters are of particular interest because they lie in front of the rich stellar backgrounds of the SMC and the Galactic bulge, respectively. We base our microlensing rate estimates for these GCs on our models of 47 Tuc (Ye et al 2021) and M22 (Kremer et al 2019) that best match these clusters' observed surface brightness and velocity dispersion profiles, as determined by the χ 2 fitting methodology described by Kremer et al (2019) and Rui et al (2021a).…”

Section: Tuc and M22mentioning

confidence: 99%

“…To match 47 Tuc, Ye et al (2021) vary the initial number of stars, density profile, binary fraction, virial radius, tidal radius, and IMF. The density profile of the bestfitting model is an Elson profile (Elson et al 1987) with γ = 2.1.…”

Section: Tuc and M22mentioning

confidence: 99%

“…In addition to predicting microlensing rates for compact objects, we also estimate the rates for M dwarfs, which usually dominate the cluster mass function in our models. In the rate analysis, we give additional attention to the clusters 47 Tuc (Ye et al 2021) andM22 (Kremer et al 2019) given the higher potential for microlensing events provided by these clusters' densely-populated backgrounds on the sky, i.e., the Small Magellanic Cloud (SMC) and the Galactic bulge, respectively. This paper is structured as follows.…”

Section: Introductionmentioning

confidence: 99%

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Gravitational Microlensing Rates in Milky Way Globular Clusters

Kıroğlu,

Weatherford,

Kremer

et al. 2021

Preprint

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Many recent observational and theoretical studies suggest globular clusters (GCs) host compact object populations large enough to play dominant roles governing their overall dynamical evolution. Yet direct detection, particularly of black holes and neutron stars, remains rare and limited to special cases, such as when these objects reside in close binaries with bright companions. Here we examine the potential of microlensing detections to further constrain these dark populations. Based on stateof-the-art GC models from the CMC Cluster Catalog, we estimate the microlensing event rates for black holes, neutron stars, white dwarfs, and, for comparison, also for M dwarfs in Milky Way GCs, as well as the effects of different initial conditions on these rates. Among compact objects, we find that white dwarfs dominate the microlensing rates, simply because they dominate by numbers. We show that microlensing detections are in general more likely in GCs with higher initial densities, especially in clusters that undergo core-collapse where the lenses are white dwarfs. We also estimate microlensing rates in the specific cases of M22 and 47 Tuc using our best-fitting models for these GCs. Because their positions on the sky lie near the rich stellar backgrounds of the Galactic bulge and the Small Magellanic Cloud, respectively, these clusters are among the Galactic GCs best-suited for dedicated microlensing surveys.

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Section: Tuc and M22mentioning

confidence: 99%

Section: Tuc and M22mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gravitational Microlensing Rates in Milky Way Globular Clusters

Kıroğlu,

Weatherford,

Kremer

et al. 2021

Preprint

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“…It is now routine to create entire grids of 𝑁-body star cluster models with > 10 6 stars and binaries covering a realistic range of initial conditions that can reproduce GCs and other massive star clusters in the local universe. But while this approach has had great success creating models of individual star clusters in the MW (e.g., van der Marel et al 1997;Hurley et al 2001;Baumgardt et al 2003;Heggie & Giersz 2014;Heggie 2014;Wang et al 2016a;Kremer et al 2018;Ye et al 2021), near every study of galactic and extra-galactic GC systems has started from idealized grids of initial conditions designed only to reproduce MW GCs. While this method allows us to create one-to-one mappings between individual MW clusters and 𝑁-body models (e.g., Baumgardt & Hilker 2018;Weatherford et al 2020;Rui et al 2021b), it neglects the wealth of information that cosmological models of star cluster formation can provide, such as the cluster initial mass function (CIMF), initial radii, metallicities, ages, galactic tidal fields, and more.…”

Section: Introductionmentioning

confidence: 99%

Great Balls of FIRE II: The evolution and destruction of star clusters across cosmic time in a Milky Way-mass galaxy

Rodriguez,

Hafen,

Grudić

et al. 2022

Preprint

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The current generation of galaxy simulations can resolve individual giant molecular clouds, the progenitors of dense star clusters. But the evolutionary fate of these young massive clusters (YMCs), and whether they can become the old globular clusters (GCs) observed in many galaxies, is determined by a complex interplay of internal dynamical processes and external galactic effects. We present the first star-by-star 𝑁-body models of massive (𝑁 ∼ 10 5 − 10 7 ) star clusters formed in a FIRE-2 MHD simulation of a Milky Way-mass galaxy, with all of the relevant initial conditions and galactic tidal effects extracted directly from the cosmological simulation. We randomly select 895 (∼ 30%) of the YMCs with > 6 × 10 4 𝑀 from Grudić et al. 2022 and integrate them to the present day using the Cluster Monte Carlo Code, CMC. This procedure predicts a MW-like system with 148 GCs, most of which were formed during the early, bursty mode of star formation in the galaxy. Our GCs are younger, less massive, and more core collapsed than clusters in the Milky Way or M31. This is a direct result of the assembly history and age-metallicity relationship of the GCs' host galaxy: younger clusters are preferentially born in stronger galactic tidal fields and initially retain fewer stellar-mass black holes, causing them to lose mass faster and reach core collapse sooner than their older counterparts. Our results suggest that the masses and core/half-light radii of GCs are shaped not only by internal dynamical processes, but by the specific evolutionary history of their host galaxies as well. These results emphasize that 𝑁-body studies with realistic stellar physics are crucial to understanding the evolution and present-day properties of galactic GC systems.

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“…The high densities within the centers of core-collapsed clusters lead naturally to an increased rate of close stellar encounters of these objects, and therefore, an increased rate of stellar collisions and tidal disruptions (e.g., Heggie & Hut 2003). A number of studies have shown that close tidal interactions involving specifically neutron stars and stars may lead to the formation of compact binaries (e.g., Fabian et al 1975;Ray et al 1987;Ivanova et al 2005;Ye et al 2021). Even closer encounters inevitably lead to collisions of neutron stars and stars (e.g., Krolik et al 1984;Rasio & Shapiro 1991;Lombardi et al 2006;Perets et al 2016;Kremer et al 2019b).…”

mentioning

confidence: 99%

Formation of Low-mass Black Holes and Single Millisecond Pulsars in Globular Clusters

Kremer,

Ye,

Kıroğlu

et al. 2022

Preprint

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Close encounters between neutron stars and main-sequence stars occur in globular clusters and may lead to various outcomes. Here we study encounters resulting in tidal disruption of the star. Using N -body models, we predict the typical stellar masses in these disruptions and the dependence of the event rate on host cluster properties. We find that tidal disruption events occur most frequently in core-collapsed globular clusters and that roughly 25% of the disrupted stars are merger products (i.e., blue straggler stars). Using hydrodynamic simulations, we model the tidal disruptions themselves (over timescales of days) to determine the mass bound to the neutron star and the properties of the remnant disks formed. Depending on the impact parameter and mass of the disrupted star, we find disk masses ranging from roughly 0.1 − 1 M and typical radii of a few R . Additionally, we find that neutron stars receive impulsive kicks of up to about 20 km/s as a result of the asymmetry of unbound ejecta; these kicks place these neutron stars on elongated orbits within their host cluster, with apocenter distances well outside the cluster core. Finally, we model the evolution of the (hypercritical) accretion disks on longer timescales (days to years after disruption) to estimate the accretion rate onto the neutron stars and accompanying spin-up. As long as 1% of the bound mass accretes onto the neutron star, millisecond spin periods can be attained. We argue the growing numbers of isolated millisecond pulsars observed in globular clusters may have formed, at least in part, through this mechanism. In the case of significant mass growth, some of these neutron stars may collapse to form low-mass ( 3 M ) black holes.

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Compact Object Modeling in the Globular Cluster 47 Tucanae

Cited by 4 publications

References 108 publications

Gravitational Microlensing Rates in Milky Way Globular Clusters

Gravitational Microlensing Rates in Milky Way Globular Clusters

Great Balls of FIRE II: The evolution and destruction of star clusters across cosmic time in a Milky Way-mass galaxy

Formation of Low-mass Black Holes and Single Millisecond Pulsars in Globular Clusters

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