Abstract
Palomar 5 is one of the sparsest star clusters in the Galactic halo and is best known for its spectacular tidal tails, spanning over 20° across the sky. With N-body simulations, we show that both distinguishing features can result from a stellar-mass black hole population, comprising ~20% of the present-day cluster mass. In this scenario, Palomar 5 formed with a ‘normal’ black hole mass fraction of a few per cent, but stars were lost at a higher rate than black holes, such that the black hole fraction gradually increased. This inflated the cluster, enhancing tidal stripping and tail formation. A billion years from now, the cluster will dissolve as a 100% black hole cluster. Initially denser clusters end up with lower black hole fractions, smaller sizes and no observable tails. Black hole-dominated, extended star clusters are therefore the likely progenitors of the recently discovered thin stellar streams in the Galactic halo.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 digital issues and online access to articles
$119.00 per year
only $9.92 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
A snapshot of the wBH-1 model is published on Zenodo (https://doi.org/10.5281/zenodo.4739181). All N-body data are available upon request from the corresponding author.
Code availability
NBODY6++GPU is available from https://github.com/nbodyx/Nbody6ppGPU. LIMEPY is available from https://github.com/mgieles/limepy.
References
Bernard, E. J. et al. A synoptic map of halo substructures from the Pan-STARRS1 3π survey. Mon. Not. R. Astron. Soc. 463, 1759–1768 (2016).
Shipp, N. et al. Stellar streams discovered in the dark energy survey. Astrophys. J. 862, 114 (2018).
Malhan, K., Ibata, R. A. & Martin, N. F. Ghostly tributaries to the Milky Way: charting the halo’s stellar streams with the Gaia DR2 catalogue. Mon. Not. R. Astron. Soc. 481, 3442–3455 (2018).
Ibata, R. A., Malhan, K. & Martin, N. F. The streams of the gaping abyss: a population of entangled stellar streams surrounding the inner galaxy. Astrophys. J. 872, 152 (2019).
Koposov, S. E., Rix, H.-W. & Hogg, D. W. Constraining the Milky Way potential with a six-dimensional phase-space map of the GD-1 stellar stream. Astrophys. J. 712, 260–273 (2010).
de Boer, T. J. L., Erkal, D. & Gieles, M. A closer look at the spur, blob, wiggle, and gaps in GD-1. Mon. Not. R. Astron. Soc. 494, 5315–5332 (2020).
Baumgardt, H. & Makino, J. Dynamical evolution of star clusters in tidal fields. Mon. Not. R. Astron. Soc. 340, 227–246 (2003).
Kuzma, P. B., Da Costa, G. S. & Mackey, A. D. The outer envelopes of globular clusters. II. NGC 1851, NGC 5824 and NGC 1261*. Mon. Not. R. Astron. Soc. 473, 2881–2898 (2018).
Myeong, G. C., Evans, N. W., Belokurov, V., Sanders, J. L. & Koposov, S. E. The sausage globular clusters. Astrophys. J. Lett. 863, L28 (2018).
Odenkirchen, M. et al. Detection of massive tidal tails around the globular cluster Palomar 5 with Sloan Digital Sky Survey commissioning data. Astrophys. J. Lett. 548, L165–L169 (2001).
Ibata, R. A., Lewis, G. F., Thomas, G., Martin, N. F. & Chapman, S. Feeling the pull: a study of natural galactic accelerometers. II. Kinematics and mass of the delicate stellar stream of the Palomar 5 globular cluster. Astrophys. J. 842, 120 (2017).
Dehnen, W., Odenkirchen, M., Grebel, E. K. & Rix, H.-W. Modeling the disruption of the globular cluster Palomar 5 by galactic tides. Astron. J. 127, 2753–2770 (2004).
Smith, G. H., Sneden, C. & Kraft, R. P. A study of abundances of four giants in the low-mass globular cluster Palomar 5. Astron. J. 123, 1502–1508 (2002).
Elmegreen, B. G. Globular cluster formation at high density: a model for elemental enrichment with fast recycling of massive-star debris. Astrophys. J. 836, 80 (2017).
Gieles, M. et al. Concurrent formation of supermassive stars and globular clusters: implications for early self-enrichment. Mon. Not. R. Astron. Soc. 478, 2461–2479 (2018).
Gieles, M., Heggie, D. C. & Zhao, H. The life cycle of star clusters in a tidal field. Mon. Not. R. Astron. Soc. 413, 2509–2524 (2011).
Abbott, B. P. et al. Observation of gravitational waves from a binary black hole merger. Phys. Rev. Lett. 116, 061102 (2016).
Rodriguez, C. L., Chatterjee, S. & Rasio, F. A. Binary black hole mergers from globular clusters: masses, merger rates, and the impact of stellar evolution. Phys. Rev. D 93, 084029 (2016).
Antonini, F. & Gieles, M. Merger rate of black hole binaries from globular clusters: theoretical error bars and comparison to gravitational wave data from GWTC-2. Phys. Rev. D 102, 123016 (2020).
Fryer, C. L. & Kalogera, V. Theoretical black hole mass distributions. Astrophys. J. 554, 548–560 (2001).
Fryer, C. L. et al. Compact remnant mass function: dependence on the explosion mechanism and metallicity. Astrophys. J. 749, 91 (2012).
Merritt, D., Piatek, S., Portegies Zwart, S. & Hemsendorf, M. Core formation by a population of massive remnants. Astrophys. J. Lett. 608, L25–L28 (2004).
Mackey, A. D., Wilkinson, M. I., Davies, M. B. & Gilmore, G. F. Black holes and core expansion in massive star clusters. Mon. Not. R. Astron. Soc. 386, 65–95 (2008).
Giersz, M. et al. MOCCA survey data base- I. Dissolution of tidally filling star clusters harbouring black hole subsystems. Mon. Not. R. Astron. Soc. 487, 2412–2423 (2019).
Wang, L. The survival of star clusters with black hole subsystems. Mon. Not. R. Astron. Soc. 491, 2413–2423 (2020).
Strader, J., Chomiuk, L., Maccarone, T. J., Miller-Jones, J. C. A. & Seth, A. C. Two stellar-mass black holes in the globular cluster M22. Nature 490, 71–73 (2012).
Chomiuk, L. et al. A radio-selected black hole X-ray binary candidate in the milky way globular cluster M62. Astrophys. J. 777, 69 (2013).
Giesers, B. et al. A detached stellar-mass black hole candidate in the globular cluster NGC 3201. Mon. Not. R. Astron. Soc. 475, L15–L19 (2018).
Wang, L. et al. NBODY6++GPU: ready for the gravitational million-body problem. Mon. Not. R. Astron. Soc. 450, 4070–4080 (2015).
Banerjee, S. et al. BSE versus StarTrack: Implementations of new wind, remnant-formation, and natal-kick schemes in NBODY7 and their astrophysical consequences. Astron. Astrophys. 639, A41 (2020).
Hurley, J. R. Ratios of star cluster core and half-mass radii: a cautionary note on intermediate-mass black holes in star clusters. Mon. Not. R. Astron. Soc. 379, 93–99 (2007).
Peuten, M., Zocchi, A., Gieles, M., Gualandris, A. & Hénault-Brunet, V. A stellar-mass black hole population in the globular cluster NGC 6101? Mon. Not. R. Astron. Soc. 462, 2333–2342 (2016).
Breen, P. G. & Heggie, D. C. Dynamical evolution of black hole subsystems in idealized star clusters. Mon. Not. R. Astron. Soc. 432, 2779–2797 (2013).
Erkal, D., Koposov, S. E. & Belokurov, V. A sharper view of Pal 5’s tails: discovery of stream perturbations with a novel non-parametric technique. Mon. Not. R. Astron. Soc. 470, 60–84 (2017).
Banik, N. & Bovy, J. Effects of baryonic and dark matter substructure on the Pal 5 stream. Mon. Not. R. Astron. Soc. 484, 2009–2020 (2019).
Kuzma, P. B., Da Costa, G. S., Keller, S. C. & Maunder, E. Palomar 5 and its tidal tails: a search for new members in the tidal stream. Mon. Not. R. Astron. Soc. 446, 3297–3309 (2015).
Banerjee, S. & Kroupa, P. A new type of compact stellar population: dark star clusters. Astrophys. J. Lett. 741, L12 (2011).
Baumgardt, H., Parmentier, G., Gieles, M. & Vesperini, E. Evidence for two populations of Galactic globular clusters from the ratio of their half-mass to Jacobi radii. Mon. Not. R. Astron. Soc. 401, 1832–1838 (2010).
Baumgardt, H. & Hilker, M. A catalogue of masses, structural parameters, and velocity dispersion profiles of 112 Milky Way globular clusters. Mon. Not. R. Astron. Soc. 478, 1520–1557 (2018).
Elmegreen, B. G. The globular cluster mass function as a remnant of violent birth. Astrophys. J. Lett. 712, L184–L188 (2010).
Kruijssen, J. M. D. Globular clusters as the relics of regular star formation in ‘normal’ high-redshift galaxies. Mon. Not. R. Astron. Soc. 454, 1658–1686 (2015).
Spitzer, L.Jr Disruption of galactic clusters. Astrophys. J. 127, 17 (1958).
Gieles, M. et al. Star cluster disruption by giant molecular clouds. Mon. Not. R. Astron. Soc. 371, 793–804 (2006).
Gieles, M. & Renaud, F. If it does not kill them, it makes them stronger: collisional evolution of star clusters with tidal shocks. Mon. Not. R. Astron. Soc. 463, L103–L107 (2016).
Massari, D., Koppelman, H. H. & Helmi, A. Origin of the system of globular clusters in the Milky Way. Astron. Astrophys. 630, L4 (2019).
Bianchini, P., Renaud, F., Gieles, M. & Varri, A. L. The inefficiency of satellite accretion in forming extended star clusters. Mon. Not. R. Astron. Soc. 447, L40–L44 (2015).
Chatterjee, S., Rodriguez, C. L. & Rasio, F. A. Binary black holes in dense star clusters: exploring the theoretical uncertainties. Astrophys. J. 834, 68 (2017).
Kim, J.-h. et al. Formation of globular cluster candidates in merging proto-galaxies at high redshift: a view from the FIRE cosmological simulations. Mon. Not. R. Astron. Soc. 474, 4232–4244 (2018).
Kremer, K. et al. Modeling dense star clusters in the Milky Way and beyond with the CMC cluster catalog. Astrophys. J. Suppl. Ser. 247, 48 (2020).
Vesperini, E. Evolution of globular cluster systems in elliptical galaxies - II. Power-law initial mass function. Mon. Not. R. Astron. Soc. 322, 247–256 (2001).
Fall, S. M. & Zhang, Q. Dynamical evolution of the mass function of globular star clusters. Astrophys. J. 561, 751–765 (2001).
Sollima, A., Martínez-Delgado, D., Valls-Gabaud, D. & Peñarrubia, J. Discovery of tidal tails around the distant globular cluster Palomar 14. Astrophys. J. 726, 47 (2011).
Bovy, J. galpy: a Python library for galactic dynamics. Astrophys. J. Suppl. Ser. 216, 29 (2015).
Price-Whelan, A. M. et al. Kinematics of the Palomar 5 stellar stream from RR lyrae stars. Astron. J. 158, 223 (2019).
Vasiliev, E. Proper motions and dynamics of the Milky Way globular cluster system from Gaia DR2. Mon. Not. R. Astron. Soc. 484, 2832–2850 (2019).
Gravity Collaboration et al. A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty. Astron. Astrophys. 625, L10 (2019).
Navarro, J. F., Frenk, C. S. & White, S. D. M. The structure of cold dark matter halos. Astrophys. J. 462, 563 (1996).
Miyamoto, M. & Nagai, R. Three-dimensional models for the distribution of mass in galaxies. Publ. Astron. Soc. Jpn 27, 533–543 (1975).
Hernquist, L. An analytical model for spherical galaxies and bulges. Astrophys. J. 356, 359–364 (1990).
Martell, S. L., Smith, G. H. & Grillmair, C. J. A new age measurement for Palomar 5. In American Astronomical Society Meeting Abstracts Vol. 201, 07.11 (American Astronomical Society, 2002).
Dotter, A., Sarajedini, A. & Anderson, J. Globular clusters in the outer galactic halo: new Hubble Space Telescope/Advanced Camera for Surveys imaging of six globular clusters and the galactic globular cluster age-metallicity relation. Astrophys. J. 738, 74 (2011).
Xu, X. et al. New determination of fundamental properties of Palomar 5 using deep DESI imaging data. Astron. J. 161, 12 (2021).
Plummer, H. C. On the problem of distribution in globular star clusters. Mon. Not. R. Astron. Soc. 71, 460–470 (1911).
Kroupa, P. On the variation of the initial mass function. Mon. Not. R. Astron. Soc. 322, 231–246 (2001).
Aarseth, S. J. From NBODY1 to NBODY6: the growth of an industry. Publ. Astron. Soc. Pac. 111, 1333–1346 (1999).
Aarseth, S. J. Gravitational N-Body Simulations (Cambridge Univ. Press, 2003).
Ahmad, A. & Cohen, L. A numerical integration scheme for the N-body gravitational problem. J. Comput. Phys. 12, 389–402 (1973).
Makino, J. & Aarseth, S. J. On a Hermite integrator with Ahmad-Cohen scheme for gravitational many-body problems. Publ. Astron. Soc. Jpn 44, 141–151 (1992).
Hurley, J. R., Pols, O. R. & Tout, C. A. Comprehensive analytic formulae for stellar evolution as a function of mass and metallicity. Mon. Not. R. Astron. Soc. 315, 543–569 (2000).
Hurley, J. R., Tout, C. A. & Pols, O. R. Evolution of binary stars and the effect of tides on binary populations. Mon. Not. R. Astron. Soc. 329, 897–928 (2002).
Nitadori, K. & Aarseth, S. J. Accelerating NBODY6 with graphics processing units. Mon. Not. R. Astron. Soc. 424, 545–552 (2012).
Hobbs, G., Lorimer, D. R., Lyne, A. G. & Kramer, M. A statistical study of 233 pulsar proper motions. Mon. Not. R. Astron. Soc. 360, 974–992 (2005).
Belczynski, K. et al. Compact object modeling with the startrack population synthesis code. Astrophys. J. Suppl. Ser. 174, 223–260 (2008).
King, I. R. The structure of star clusters. III. Some simple dynamical models. Astron. J. 71, 64 (1966).
Ibata, R. et al. Do globular clusters possess dark matter haloes? A case study in NGC 2419. Mon. Not. R. Astron. Soc. 428, 3648–3659 (2013).
Gieles, M. & Zocchi, A. A family of lowered isothermal models. Mon. Not. R. Astron. Soc. 454, 576–592 (2015).
Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: the MCMC hammer. Publ. Astron. Soc. Pac. 125, 306–312 (2013).
Choi, J. et al. Mesa Isochrones and Stellar Tracks (MIST). I. Solar-scaled models. Astrophys. J. 823, 102 (2016).
Dotter, A. MESA Isochrones and Stellar Tracks (MIST) 0: methods for the construction of stellar isochrones. Astrophys. J. Suppl. Ser. 222, 8 (2016).
Ibata, R. A., Lewis, G. F. & Martin, N. F. Feeling the pull: a study of natural galactic accelerometers. I. Photometry of the delicate stellar stream of the Palomar 5 globular cluster. Astrophys. J. 819, 1 (2016).
Cottaar, M., Meyer, M. R. & Parker, R. J. Characterizing a cluster’s dynamic state using a single epoch of radial velocities. Astron. Astrophys. 547, A35 (2012).
Heggie, D. C. Binary evolution in stellar dynamics. Mon. Not. R. Astron. Soc. 173, 729–787 (1975).
Giesers, B. et al. A stellar census in globular clusters with MUSE: binaries in NGC 3201. Astron. Astrophys. 632, A3 (2019).
Kremer, K., Ye, C. S., Chatterjee, S., Rodriguez, C. L. & Rasio, F. A. How black holes shape globular clusters: modeling NGC 3201. Astrophys. J. Lett. 855, L15 (2018).
Alessandrini, E., Lanzoni, B., Ferraro, F. R., Miocchi, P. & Vesperini, E. Investigating the mass segregation process in globular clusters with blue straggler stars: the impact of dark remnants. Astrophys. J. 833, 252 (2016).
Weatherford, N. C., Chatterjee, S., Rodriguez, C. L. & Rasio, F. A. Predicting stellar-mass black hole populations in globular clusters. Astrophys. J. 864, 13 (2018).
Weatherford, N. C., Chatterjee, S., Kremer, K. & Rasio, F. A. A dynamical survey of stellar-mass black holes in 50 Milky Way globular clusters. Astrophys. J. 898, 162 (2020).
Askar, A., Arca Sedda, M. & Giersz, M. MOCCA-SURVEY Database I: galactic globular clusters harbouring a black hole subsystem. Mon. Not. R. Astron. Soc. 478, 1844–1854 (2018).
Rodriguez, C. L. et al. Million-body star cluster simulations: comparisons between Monte Carlo and direct N-body. Mon. Not. R. Astron. Soc. 463, 2109–2118 (2016).
Rodriguez, C. L. et al. A new hybrid technique for modeling dense star clusters. Comput. Astrophys. Cosmol. 5, 5 (2018).
Shu, Y. et al. Catalogues of active galactic nuclei from Gaia and unWISE data. Mon. Not. R. Astron. Soc. 489, 4741–4759 (2019).
Astropy Collaboration et al. Astropy: a community Python package for astronomy. Astron. Astrophys. 558, A33 (2013).
Astropy Collaboration et al. The Astropy Project: building an open-science project and status of the v2.0 core package. Astron. J. 156, 123 (2018).
Hénon, M. Sur l’évolution dynamique des amas globulaires. Ann. Astrophys. 24, 369 (1961).
Acknowledgements
M.G. and E.B. acknowledge financial support from the European Research Council (grant number ERC StG-335936, CLUSTERS) and M.G. acknowledges support from the Spanish Ministry of Science and Innovation through a Europa Excelencia grant (EUR2020-112157). F.A. acknowledges support from a Rutherford fellowship (grant number ST/P00492X/2) from the Science and Technology Facilities Council. E.B. acknowledges financial support from a Vici grant from the Netherlands Organisation for Scientific Research (NWO). M.G. thanks G. Pérez Forcadell for installing the GPU server at the ICCUB on which all the simulations were run. We thank R. Ibata for sharing the data of Pal 5’s surface density profile, Ł. Wyrzykowski for discussions on microlensing and S. Aarseth, K. Nitadori and L. Wang for maintaining NBODY6 and NBODY6++GPU and making the codes publicly available. M.G. and F.A. thank L. Wang and S. Banerjee for discussions on the recent SSE and BSE updates and the implementation in NBODY6++GPU. This research made use of ASTROPY, a community-developed core Python package for astronomy92,93 (http://www.astropy.org).
Author information
Authors and Affiliations
Contributions
M.G. ran all N-body simulations, analysed them and was in charge of the writing. D.E. was in charge of stream modelling and deriving the orbit of Pal 5 and the parameters of the MW model. F.A. contributed to the BH physics of the N-body models. E.B. converted stream models to observed quantities and J.P. contributed to the binary properties. All authors assisted in the development, analysis and writing of the paper.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Peer review information Nature Astronomy thanks the anonymous reviewers for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Supplementary Information
Supplementary Fig. 1, Table 1 and Methods.
Rights and permissions
About this article
Cite this article
Gieles, M., Erkal, D., Antonini, F. et al. A supra-massive population of stellar-mass black holes in the globular cluster Palomar 5. Nat Astron 5, 957–966 (2021). https://doi.org/10.1038/s41550-021-01392-2
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41550-021-01392-2