Testing the Kerr nature of stellar-mass black hole candidates by combining the continuum-fitting method and the power estimate of transient ballistic jets

Astrophysical black hole candidates are thought to be the Kerr black holes predicted by General Relativity, as these objects cannot be explained otherwise without introducing new physics. However, there is no observational evidence that the space-time around them is really described by the Kerr solution. The Kerr black hole hypothesis can be tested with the already available X-ray data by extending the continuum-fitting method, a technique currently used by astronomers to estimate the spins of stellar-mass black hole candidates. In general, we cannot put a constraint on possible deviations from the Kerr geometry, but only on some combination between these deviations and the spin. The measurement of the radio power of transient jets in black hole binaries can potentially break this degeneracy, thus allowing for testing the Kerr-nature of these objects.

Figure 1

Braneworld-inspired black holes of Eq. (3). Plots of the jet power $P_{\mathrm{jet}}$ against the BH angular frequency ${\Omega }_H$. The top left panel shows the data in the case of the familiar Kerr background and the dotted line corresponds to $P_{\mathrm{jet}}\sim {\Omega }_H^2$, the theoretical scaling derived in Ref. 22.

Figure 2

Braneworld-inspired black holes of Eq. (3). Accretion efficiency $\eta =1-E_{\mathrm{ISCO}}$ (left panel) and BH angular frequency ${\Omega }_H$ (right panel) as a function of the spin parameter $a_{*}$ for different values of $\beta /M^2$.

Figure 3

Braneworld-inspired black holes of Eq. (3). Allowed regions in the parameter space $(a_{*},\beta /M^2)$ for the BH candidates GRS 1915+105 and XTE J1550-564 (left panel) and GRO J1655-40 and A0620-00 (right panel). The solid curve separates BHs from naked singularities. See text for details.

Figure 4

JP black holes of Eq. (6) with deformation parameter ${ϵ}_3$ and ${ϵ}_i=0$ for $i\ne 3$. Accretion efficiency $\eta =1-E_{\mathrm{ISCO}}$ as a function of the spin parameter $a_{*}$ for different values of ${ϵ}_3$.

Figure 5

JP black holes of Eq. (6) with deformation parameter ${ϵ}_3$ and ${ϵ}_i=0$ for $i\ne 3$. Allowed regions in the parameter space $(a_{*},{ϵ}_3)$ for the BH candidates GRS 1915+105 and XTE J1550-564 (left panel) and GRO J1655-40 and A0620-00 (right panel). See text for details.

Figure 6

JP black holes of Eq. (6) with deformation parameter ${ϵ}_3$ and ${ϵ}_i=0$ for $i\ne 3$. Plots of the jet power $P_{\mathrm{jet}}$ against the BH spin parameter $a_{*}$. The top left panel shows the data in the case of the familiar Kerr background and the dotted curve corresponds to $P_{\mathrm{jet}}\sim {\Omega }_H^2$, the theoretical scaling derived in Ref. 22.