The effects of a background potential in star cluster evolution

Reinoso, B.; Schleicher, Dominik R. G.; Fellhauer, M.; Leigh, Nathan W. C.; Klessen, Ralf S.

doi:10.1051/0004-6361/202037843

Cited by 20 publications

(10 citation statements)

References 50 publications

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“…Many other works have considered the formation of massive stars, typically in the regime of runaway collisions and in the context of the formation of the first massive black holes to form in the Universe (e.g. Devecchi & Volonteri 2009;Katz, Sijacki, & Haehnelt 2015;Sakurai et al 2017;Reinoso et al 2020). It has also been suggested that stellar collisions may be important in nuclear stellar clusters, where a massive black hole would be the inevitable outcome for very dense systems (e.g.…”

Section: Introductionmentioning

confidence: 99%

Small-N Collisional Dynamics V: Beyond the Realm of Not-So-Small-N

Barrera,

Leigh,

Reinoso

et al. 2020

Preprint

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Direct collisions between finite-sized particles occur commonly in many areas of astrophysics. Such collisions are typically mediated by chaotic, bound gravitational interactions involving small numbers of particles. An important application is stellar collisions, which occur commonly in dense star clusters, and their relevance for the formation of various types of stellar exotica. In this paper, we return to our study of the collision rates and probabilities during small-number chaotic gravitational interactions (N 10), moving beyond the small-number particle limit and into the realm of larger particle numbers (N 10 3 ) to test the extent of validity of our analytic model as a function of the particle properties and the number of interacting particles. This is done using direct N -body simulations of stellar collisions in dense star clusters, by varying the relative numbers of particles with different particle masses and radii. We compute the predicted rate of collisions using the mean free path approximation, adopting the point-particle limit and using the sticky-star approximation as our collision criterion. We evaluate its efficacy in the regime where gravitational-focusing is important by comparing the theoretical rates to numerical simulations. Using the tools developed in previous papers in this series, in particular Collision Rate Diagrams, we illustrate that our predicted and simulated rates are in excellent agreement, typically consistent with each other to within one standard deviation.

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Section: Introductionmentioning

confidence: 99%

Small-N Collisional Dynamics V: Beyond the Realm of Not-So-Small-N

Barrera,

Leigh,

Reinoso

et al. 2020

Preprint

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“…To analyze the dynamics of the protostellar cluster, we adopt the formulation of Reinoso et al (2020), who extended the framework of Spitzer (1987) to include the effect of a gas potential. The crossing time of the cluster is then given as…”

Section: Stellar Crossing and Relaxation Timementioning

confidence: 99%

Origin of supermassive black holes in massive metal-poor protoclusters

Schleicher,

Reinoso,

Latif

et al. 2022

Preprint

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While large numbers of supermassive black holes have been detected at 𝑧 > 6, their origin is still essentially unclear. Numerical simulations have shown that the conditions for the classical direct collapse scenario are very restrictive and fragmentation is very difficult to be avoided. We thus consider here a more general case of a dense massive protostar cluster at low metallicity ( 10 −3 Z ) embedded in gas. We estimate the mass of the central massive object, formed via collisions and gas accretion, considering the extreme cases of a logarithmically flat and a Salpeter-type initial mass function. Objects with masses of at least 10 4 M could be formed for inefficient radiative feedback, whereas ∼ 10 3 M objects could be formed when the accretion time is limited via feedback. These masses will vary depending on the environment and could be considerably larger, particularly due to the continuous infall of gas into the cloud. As a result, one may form intermediate mass black holes of ∼ 10 4 M or more. Upcoming observations with the James Webb Space Telescope (JWST) and other observatories may help to detect such massive black holes and their environment, thereby shedding additional light on such a formation channel.

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“…Another formation scenario involves the collisions and mergers of stars in a massive cluster with a high stellar density (Devecchi et al 2010;Katz et al 2015;Sakurai et al 2017Sakurai et al , 2019Reinoso et al 2018Reinoso et al , 2020. In particular in the context of primordial protostellar clusters, results from stellar evolution calculations suggest that collisions could play a large role, as the radii of these stars could be considerably enhanced depending on the accretion rate.…”

Section: Introductionmentioning

confidence: 99%

Stellar collisions in flattened and rotating Population III star clusters

Vergara

Schleicher

Boekholt³

et al. 2021

A&A

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Fragmentation often occurs in disk-like structures, both in the early Universe and in the context of present-day star formation. Supermassive black holes (SMBHs) are astrophysical objects whose origin is not well understood; they weigh millions of solar masses and reside in the centers of galaxies. An important formation scenario for SMBHs is based on collisions and mergers of stars in a massive cluster with a high stellar density, in which the most massive star moves to the center of the cluster due to dynamical friction. This increases the rate of collisions and mergers since massive stars have larger collisional cross sections. This can lead to a runaway growth of a very massive star which may collapse to become an intermediate-mass black hole. Here we investigate the dynamical evolution of Miyamoto-Nagai models that allow us to describe dense stellar clusters, including flattening and different degrees of rotation. We find that the collisions in these clusters depend mostly on the number of stars and the initial stellar radii for a given radial size of the cluster. By comparison, rotation seems to affect the collision rate by at most 20%. For flatness, we compared spherical models with systems that have a scale height of about 10% of their radial extent, in this case finding a change in the collision rate of less than 25%. Overall, we conclude that the parameters only have a minor effect on the number of collisions. Our results also suggest that rotation helps to retain more stars in the system, reducing the number of escapers by a factor of 2−3 depending on the model and the specific realization. After two million years, a typical lifetime of a very massive star, we find that about 630 collisions occur in a typical models with N = 104, R = 100 R⊙ and a half-mass radius of 0.1 pc, leading to a mass of about 6.3 × 103 M⊙ for the most massive object. We note that our simulations do not include mass loss during mergers or due to stellar winds. On the other hand, the growth of the most massive object may subsequently continue, depending on the lifetime of the most massive object.

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The effects of a background potential in star cluster evolution

Cited by 20 publications

References 50 publications

Small-N Collisional Dynamics V: Beyond the Realm of Not-So-Small-N

Small-N Collisional Dynamics V: Beyond the Realm of Not-So-Small-N

Origin of supermassive black holes in massive metal-poor protoclusters

Stellar collisions in flattened and rotating Population III star clusters

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