Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2006.10771

Populating the upper black hole mass gap through stellar collisions in young star clusters

Kyle Kremer·Mario Spera·Devin Becker·Sourav Chatterjee·Ugo N. Di Carlo·Giacomo Fragione·Carl L. Rodriguez·Claire S. Ye·Frederic A. Rasio
View original source ↗Read source document ↗Export metadata ↓

Abstract

Theoretical modeling of massive stars predicts a gap in the black hole (BH) mass function above $\sim 40-50\,M_{\odot}$ for BHs formed through single star evolution, arising from (pulsational) pair-instability supernovae. However, in dense star clusters, dynamical channels may exist that allow construction of BHs with masses in excess of those allowed from single star evolution. The detection of BHs in this so-called "upper-mass gap" would provide strong evidence for the dynamical processing of BHs prior to their eventual merger. Here, we explore in detail the formation of BHs with masses within or above the pair-instability gap through collisions of young massive stars in dense star clusters. We run a suite of 68 independent cluster simulations, exploring a variety of physical assumptions pertaining to growth through stellar collisions, including primordial cluster mass segregation and the efficiency of envelope stripping during collisions. We find that as many as $\sim20\%$ of all BH progenitors undergo one or more collisions prior to stellar collapse and up to $\sim1\%$ of all BHs reside within or above the pair-instability gap through the effects of these collisions. We show that these BHs readily go on to merge with other BHs in the cluster, creating a population of massive BH mergers at a rate that may compete with the "multiple-generation" merger channel described in other analyses. This has clear relevance for the formation of very massive BH binaries as recently detected by LIGO/Virgo in GW190521. Finally, we describe how stellar collisions in clusters may provide a unique pathway to pair-instability supernovae and briefly discuss the expected rate of these events and other electromagnetic transients.

Explore related subjects

astro-ph.HE

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Kyle Kremer, Mario Spera, Devin Becker, Sourav Chatterjee, Ugo N. Di Carlo, Giacomo Fragione, Carl L. Rodriguez, Claire S. Ye, Frederic A. Rasio. 2020-09-15. Populating the upper black hole mass gap through stellar collisions in young star clusters. https://doi.org/10.3847/1538-4357%2Fabb945

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

ExTraSS: a Domain Decomposed 3D NLTE Radiative Transfer spectral synthesis code for nebular phase transients

In the nebular phase, supernovae are powered by radioactive decay and continuously fade, while their densities have decreased enough such that the expanding nebula becomes (largely) optically thin and the entire structure contributes to the emission. Models for the nebular phase need to take Non-Local Thermodynamic Equilibrium (NLTE) effects into account, while at the same time radiative transfer effects often cannot be ignored. To account for the asymmetric morphologies of SNe, 3D input ejecta models must be used. In this work, we present the $\texttt{ExTraSS}$ (EXplosive TRAnsient Spectral Simulator) code, which has been upgraded to be fully capable of 3D NLTE radiative transfer calculations in order to generate synthetic spectra for explosive transients in the nebular phase, with a focus on supernovae. We solve a long-standing difficulty of 3D NLTE radiative transfer -- to manage generation and storage of millions of photoexcitation rates over $\gtrsim10^{5}$ of cells -- by developing a new Domain Decomposition algorithm. We describe this new methodology and general code operations in detail, and analyse convergence and accuracy for $\texttt{ExTraSS}$.

astro-ph.HE↗
arXiv2026

Searching for Black Hole Candidates in Quiescence by Using Multi-band Observations in Globular Cluster M22 (NGC 6656)

We present a multi-wavelength investigation of radio sources in the globular cluster M22 (NGC 6656) using the Karl G. Jansky Very Large Array, Chandra and Hubble Space Telescope. By cross-matching the radio and X-ray source catalogs, we identify eight radio/X-ray counterparts, of which VLA22 is the most promising stellar-mass black hole (BH) candidate. Its radio and X-ray luminosities are consistent with the established $L_{\rm X}-L_{\rm R}$ correlation for BH low-mass X-ray binaries. The observed X-ray variability supports an accreting nature. One possible optical counterpart ($M_{\mathrm{814}} \approx 16.695 \pm 0.011$ mag) is identified. Based on its inferred stellar parameters, the estimated orbital period of $P_{\rm orb} \sim 16 \pm 6~{\rm h}$ places the proposed counterpart predominantly in the BH region rather than in the NS region in the $L_{\rm X}-P_{\rm orb}$ plane. These results demonstrate the effectiveness of joint radio, X-ray, and optical observations in identifying quiescent BH candidates in globular clusters.

astro-ph.HE↗
arXiv2026

Tidal Disruption of Blanets by Supermassive Black Holes: From Test Particles to Planetary-Mass Bodies in Kerr Spacetime

Planetary-mass bodies formed in active galactic nucleus (AGN) discs, termed "blanets", may undergo tidal disruption by the central supermassive black hole (SMBH). We analyse this process in Kerr spacetime using Mino-time geodesics and the Marck tidal tensor in a parallel-transported tetrad, treating the blanet as a test particle with finite size entering through the disruption criterion. For a blanet of $100 M_{\oplus}$ and $6 R_{\oplus}$ around a $10^7 M_{\odot}$ SMBH, the tidal radius is 0.82 AU, or 8.3 gravitational radii, requiring a non-perturbative relativistic treatment. The Hills mass depends on bulk density as $M_{\rm Hills}\proptoρ_p^{-1/2}$ and is independent of blanet mass at fixed density. Rocky compositions yield a lower Hills mass than a Sun-like star, while volatile-rich compositions yield a higher value, suggesting a potential composition diagnostic. The frozen-in fallback model gives a peak time of about 15 yr and a peak luminosity of $3.7\times10^{40}$ erg/s, about $3\times10^{-5}$ of the Eddington luminosity, predicting a faint, ultraviolet-peaked transient lasting roughly a century. Scalar resonant relaxation in the surrounding nuclear star cluster may deliver blanets to disruptive orbits over $10^8$ to $10^9$ yr, implying an estimated per-AGN event rate of $10^{-7}$ to $10^{-6}$ per year. Gravitational waves from sub-Earth-mass debris fragments remain approximately nine orders of magnitude below Laser Interferometer Space Antenna sensitivity.

astro-ph.HE↗