Abstract
We develop a new technique for finding black hole solutions in modified gravity that have "stealth" hair, i.e., hair whose only gravitational effect is to tune the cosmological constant. We consider scalar-tensor theories in which gravitational waves propagate at the speed of light, and show that Einstein metrics can be painted with stealth hair provided there exists a family of geodesics always normal to spacelike surfaces. We also present a novel scalar-dressed rotating black hole that has finite scalar field at both the black hole and cosmological event horizons.
Highlights
We develop a new technique for finding black hole solutions in modified gravity that have “stealth” hair, i.e., hair of which the only gravitational effect is to tune the cosmological constant
We consider scalartensor theories in which gravitational waves propagate at the speed of light and show that, subject to a parametric constraint we specify, Einstein metrics can be painted with stealth hair, provided there exists a family of geodesics always normal to spacelike surfaces
The most important is the Kerr solution that describes the rotating black hole; most astrophysical black holes are believed to be rotating, and, the first detection of gravitational waves was from the merger of two spinning Kerr black holes [1]
Summary
The most important is the Kerr solution that describes the rotating black hole; most astrophysical black holes are believed to be rotating, and, the first detection of gravitational waves was from the merger of two spinning Kerr black holes [1] Another key objective in gravity is to explain our Universe. We focus on a particular family of modified scalar-tensor theories of gravity, developing a new technique to find, for the first time, astrophysically realistic rotating black hole solutions with a nontrivial scalar field, or stealth hair. We prove that a GR solution can be a solution to modified gravity if the scalar field is the Hamilton-Jacobi potential for a geodesic congruence in the spacetime in question This allows for a wide range of physically interesting stealth solutions; in particular, we present examples of rotating black holes with stealth hair. We will focus on the subset of theories where gravitational waves propagate at the speed of light, cT 1⁄4 1, in accord with the recent multimessenger neutron star binary merger observation [9]
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