The effect of pair-instability mass loss on black-hole mergers

¹ Astronomical Observatory, Warsaw University, Ujazdowskie 4, 00-478 Warsaw, Poland
e-mail: chrisbelczynski@gmail.com
² Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, Victoria 3800, Australia
³ School of Physics & Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
⁴ Center for Nuclear Astrophysics, Department of Physics and Astronomy, Shanghai Jiao-Tong University, Shanghai 200240, PR China
⁵ Joint Institute for Nuclear Astrophysics, 1 Cyclotron Laboratory, National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321, USA
⁶ Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia
⁷ ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), 2006 New south Wales, Australia
⁸ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
⁹ Enrico Fermi Institute, Department of Physics, Department of Astronomy and Astrophysics, and Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
¹⁰ Center for Computational Relativity and Gravitation, Rochester Institute of Technology, Rochester, New York 14623, USA
¹¹ CCS-2, MSD409, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
¹² Department of Physics and Astronomy, The University of Mississippi, University, MS 38677, USA
¹³ CENTRA, Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais 1, 1049 Lisboa, Portugal

Received: 22 May 2016
Accepted: 17 July 2016

Abstract

Context. Mergers of two stellar-origin black holes are a prime source of gravitational waves and are under intensive investigation. One crucial ingredient in their modeling has been neglected: pair-instability pulsation supernovae with associated severe mass loss may suppress the formation of massive black holes, decreasing black-hole-merger rates for the highest black-hole masses.

Aims. We demonstrate the effects of pair-instability pulsation supernovae on merger rate and mass using populations of double black-hole binaries formed through the isolated binary classical evolution channel.

Methods. The mass loss from pair-instability pulsation supernova is estimated based on existing hydrodynamical calculations. This mass loss is incorporated into the StarTrack population synthesis code. StarTrack is used to generate double black-hole populations with and without pair-instability pulsation supernova mass loss.

Results. The mass loss associated with pair-instability pulsation supernovae limits the Population I/II stellar-origin black-hole mass to 50 M_⊙, in tension with earlier predictions that the maximum black-hole mass could be as high as 100 M_⊙. In our model, neutron stars form with mass 1−2 M_⊙. We then encounter the first mass gap at 2−5 M_⊙ with the compact object absence due to rapid supernova explosions, followed by the formation of black holes with mass 5−50 M_⊙, with a second mass gap at 50−135 M_⊙ created by pair-instability pulsation supernovae and by pair-instability supernovae. Finally, black holes with masses above 135 M_⊙ may potentially form to arbitrarily high mass limited only by the extent of the initial mass function and the strength of stellar winds. Suppression of double black-hole-merger rates by pair-instability pulsation supernovae is negligible for our evolutionary channel. Our standard evolutionary model, with the inclusion of pair-instability pulsation supernovae and pair-instability supernovae, is fully consistent with the Laser Interferometric Gravitational-wave Observatory (LIGO) observations of black-hole mergers: GW150914, GW151226, and LVT151012. The LIGO results are inconsistent with high (≳ 400 km s^-1) black hole (BH) natal kicks. We predict the detection of several, and up to as many as ~60, BH-BH mergers with a total mass of 10−150 M_⊙ (most likely range: 20−80 M_⊙) in the forthcoming ~60 effective days of the LIGO O2 observations, assuming the detectors reach the optimistic target O2 sensitivity.