Observational properties of massive black hole binary progenitors

Abstract

The first directly detected gravitational waves (GW 150914) were emitted by two coalescing black holes (BHs) with masses of ~36Msun and ~29Msun. Several scenarios have been proposed to put this detection into an astrophysical context. The evolution of an isolated massive binary system is among commonly considered models. Various groups have performed detailed binary-evolution calculations that lead to BH merger events. However, the question remains open as to whether binary systems with the predicted properties really exist. The aim of this paper is to help observers to close this gap by providing spectral characteristics of massive binary BH progenitors during a phase where at least one of the companions is still non-degenerate. Stellar evolution models predict fundamental stellar parameters. Using these as input for our stellar atmosphere code (PoWR), we compute a set of models for selected evolutionary stages of massive merging BH progenitors at different metallicities. The synthetic spectra obtained from our atmosphere calculations reveal that progenitors of massive BH merger events start their lives as O2-3V stars that evolve to early-type blue supergiants before they undergo core-collapse during the Wolf-Rayet phase. When the primary has collapsed, the remaining system will appear as a wind-fed high-mass X-ray binary. We provide feedback parameters, broad band magnitudes, and spectral templates that should help to identify such binaries in the future. Comparisons of empirically determined mass-loss rates with those assumed by evolution calculations reveal significant differences. The consideration of the empirical mass-loss rates in evolution calculations will possibly entail a shift of the maximum in the predicted binary-BH merger rate to higher metallicities, that is, more candidates should be expected in our cosmic neighborhood than previously assumed.

64 pages, 30 figures, accepted for publication in Astronomy & Astrophysics, v2: typos corrected

References in corpus (27)

• Pulsational pair instability as an explanation for the most luminous supernovae
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• The effect of massive binaries on stellar populations and supernova progenitors
• Double Compact Objects III: Gravitational Wave Detection Rates
• The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
• The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars
• Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined Halpha, IR and radio analysis
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
• The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence
• On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
• Towards a unified view of inhomogeneous stellar winds in isolated supergiant stars and supergiant high mass X-ray binaries
• Wolf-Rayet stars in the Small Magellanic Cloud: I. Analysis of the single WN stars
• The extended HeII4686-emitting region in IZw18 unveiled: clues for peculiar ionizing sources
• Constraints on Core Collapse from the Black Hole Mass Function
• Properties of WNh stars in the Small Magellanic Cloud: evidence for homogeneous evolution
• Direct spectroscopic observations of clumping in O-star winds
• A spectroscopic study of blue supergiant stars in the Sculptor galaxy NGC 55: chemical evolution and distance
• Winds of low-metallicity OB-type stars: HST-COS spectroscopy in IC1613
• No breakdown of the radiatively-driven wind theory in low-metallicity environments
• Stellar Metallicity of the Extended Disk and Distance of the Spiral Galaxy NGC 3621
• A new prescription for the mass-loss rates of WC and WO stars
• Radial dependence of line profile variability in seven O9--B0.5 stars
• Discovery of X-ray Emission from the Wolf-Rayet star WR142 of oxygen subtype
• On the optical counterpart of NGC300 X-1 and the global Wolf-Rayet content of NGC300
• Stellar population of the superbubble N206 in the LMC I. Analysis of the Of-type stars
• First detection of phase-dependent colliding wind X-ray emission outside the Milky Way
• Metallicity Distribution Functions of Four Local Group dwarf galaxies

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• On the contribution of ULXs to stellar feedback: an intermediate mass black hole candidate and the population of ULXs in the low-metallicity starburst galaxy ESO 338-4
• Multi-wavelength spectroscopic analysis of the ULX Holmberg II X-1 and its nebula suggests the presence of a heavy black hole accreting from a B-type donor