Does the gravitomagnetic monopole exist? A clue from a black hole x-ray binary

The gravitomagnetic monopole is the proposed gravitational analogue of Dirac’s magnetic monopole. However, an observational evidence of this aspect of fundamental physics was elusive. Here, we employ a technique involving three primary X-ray observational methods used to measure a black hole spin to search for the gravitomagnetic monopole. These independent methods give significantly different spin values for an accreting black hole. We demonstrate that the inclusion of one extra parameter due to the gravitomagnetic monopole not only makes the spin and other parameter values inferred from the three methods consistent with each other but also makes the inferred black hole mass consistent with an independently measured value. We argue that this first indication of the gravitomagnetic monopole, within our paradigm, is not a result of fine tuning.

Figure 1

NUT parameter ($n/M$) versus the spin parameter ($a/M$) space, which is divided into a black hole region and a naked singularity region (see text) by the black dashed line. The $n/M$ versus $a/M$ constraints for GRO J1655–40 are given by (1) the green dotted curve (using only the RPM timing method), (2) the red dotted curve (using the RPM timing and line spectrum methods), and (3) the blue solid curve (using the RPM timing and continuum spectrum methods). A zoomed-in version of the latter two is shown in the inset for clarity. This figure shows that there is a range of $n/M$ and $a/M$ values for GRO J1655–40 allowed by all three methods.

Figure 2

LT precession frequency (dotted line), periastron precession frequency (dashed line), and orbital frequency (dot-dashed line) as a function of the distance ($r$) around a KTN collapsed object as predicted by the RPM. The lines are drawn for $M=6.83M_{\odot }$, $a=2.12M$, and $n=1.86M$. The observed QPO frequencies (red, black, and green points in the plot) are from Table 1 of Motta et al. [21]. This plot may be compared with Fig. 5 of Motta et al. [21] (see Sec. 5).

Figure 3

NUT parameter ($n/M$) versus the spin parameter ($a/M$) space, which is divided into a black hole region and a naked singularity region by the black dashed line. The $n/M$ versus $a/M$ constraints for GRO J1655–40 are given by (1) the green dotted curve (using only the RPM timing method), (2) the red dotted curve (using the RPM timing and line spectrum methods), and (3) the blue solid curve (using the RPM timing and continuum spectrum methods). A zoomed-in version of the latter two is shown in the inset for clarity. This figure (for the second set of the parameter values; see Sec. 5) shows that there is no range of $n/M$ and $a/M$ values for GRO J1655–40 allowed by all three methods, unlike Fig. 1.