Testing Hořava-Lifshitz gravity using thin accretion disk properties

Recently, a renormalizable gravity theory with higher spatial derivatives in four dimensions was proposed by Hořava. The theory reduces to Einstein gravity with a nonvanishing cosmological constant in IR, but it has improved UV behaviors. The spherically symmetric black hole solutions for an arbitrary cosmological constant, which represent the generalization of the standard Schwarzschild–(anti) de Sitter solution, have also been obtained for the Hořava-Lifshitz theory. The exact asymptotically flat Schwarzschild-type solution of the gravitational field equations in Hořava gravity contains a quadratic increasing term, as well as the square root of a fourth order polynomial in the radial coordinate, and it depends on one arbitrary integration constant. The IR-modified Hořava gravity seems to be consistent with the current observational data, but in order to test its viability more observational constraints are necessary. In the present paper we consider the possibility of observationally testing Hořava gravity by using the accretion disk properties around black holes. The energy flux, the temperature distribution, the emission spectrum, as well as the energy conversion efficiency are obtained, and compared to the standard general relativistic case. Particular signatures can appear in the electromagnetic spectrum, thus leading to the possibility of directly testing Hořava gravity models by using astrophysical observations of the emission spectra from accretion disks.

Figure 1

The effective potential $V_{\mathrm{eff}}(r)$ of the orbiting particles for the Kehagias-Sfetsos solution and for the Schwarzschild black hole with the same total mass $M$ for the specific angular momentum $\tilde{L}=4M$. The parameter $\omega$ of the Kehagias-Sfetsos solution is set to $0.5M^{-2}$, $1M^{-2}$, and $5M^{-2}$, respectively.

Figure 2

The energy radiated by a disk around the Kehagias-Sfetsos and Schwarzschild black holes with the same total mass $M$. The parameter $\omega$ of the Kehagias-Sfetsos solution is set to $0.5M^{-2}$, $1M^{-2}$, and $5M^{-2}$, respectively, and the flux values are normalized by $F_{\max }=1.37\times {10}^{-5}{\dot{M}}_0/M^2$, the maximal flux value for the Schwarzschild black hole.

Figure 3

The disk temperature for Kehagias-Sfetsos and Schwarzschild black holes with the same total mass $M$. The parameter $\omega$ of the Kehagias-Sfetsos solution is set to $0.5M^{-2}$, $1M^{-2}$, and $5M^{-2}$, respectively.

Figure 4

Disk spectra for Kehagias-Sfetsos and Schwarzschild black holes with the same total mass $M$. The parameter $\omega$ of the Kehagias-Sfetsos solution is set to $0.5M^{-2}$, $1M^{-2}$, and $5M^{-2}$, respectively. Here $M=1M_{\odot }$ and ${\dot{M}}_0={10}^{-12}{M}_{\odot }/\mathrm{yr}$.