Iron K$\alpha$ line of Kerr black holes with scalar hair

Abstract

Recently, a family of hairy black holes in 4-dimensional Einstein gravity minimally coupled to a complex, massive scalar field was discovered~\cite{hbh}. Besides the mass $M$ and spin angular momentum $J$, these objects are characterized by a Noether charge $Q$, measuring the amount of scalar hair, which is not associated to a Gauss law and cannot be measured at spatial infinity. Introducing a dimensionless scalar hair parameter $q$, ranging from 0 to 1, we recover (a subset of) Kerr black holes for $q=0$ and a family of rotating boson stars for $q=1$. In the present paper, we explore the possibility of measuring $q$ for astrophysical black holes with current and future X-ray missions. We study the iron K$\alpha$ line expected in the reflection spectrum of such hairy black holes and we simulate observations with Suzaku and eXTP. As a proof of concept, we point out, by analyzing a sample of hairy black holes, that current observations can already constrain the scalar hair parameter $q$, because black holes with $q$ close to 1 would have iron lines definitively different from those we observe in the available data. We conclude that a detailed scanning of the full space of solutions, together with data from the future X-ray missions, like eXTP, will be able to put relevant constraints on the astrophysical realization of Kerr black holes with scalar hair.

1+18 pages, 9 figures. v2: refereed version

References in corpus (17)

• Can environmental effects spoil precision gravitational-wave astrophysics?
• Constraining Black Hole Spin Via X-ray Spectroscopy
• Apparent shape of super-spinning black holes
• Kerr-Newman scalar clouds
• A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates
• Kerr-Newman black holes with stationary charged scalar clouds
• Testing the space-time geometry around black hole candidates with the analysis of the broad K$\alpha$ iron line
• Probing the space-time geometry around black hole candidates with the resonance models for high-frequency QPOs and comparison with the continuum-fitting method
• Constraints on the spacetime geometry around 10 stellar-mass black hole candidates from the disk's thermal spectrum
• A new spin on black hole hair
• Scalarized Hairy Black Holes
• Broad K$\alpha$ iron line from accretion disks around traversable wormholes
• The large-mass limit of cloudy black holes
• Using iron line reverberation and spectroscopy to distinguish Kerr and non-Kerr black holes
• Note on the effect of a massive accretion disk in the measurements of black hole spins
• Construction and physical properties of Kerr black holes with scalar hair
• Ergo-spheres, ergo-tori and ergo-Saturns for Kerr black holes with scalar hair

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