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| Paper IPM / Astronomy / 16779 |
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We examine the possibility for the existence of gravitomagnetic monopole (nâ) in M87* by using the results obtained from its first Event Horizon Telescope image. By numerically deducing the shadow sizes in Kerr-Taub-NUT (KTN) spacetime, we show that the shadow size increases with increasing - nâ - for a fixed Kerr parameter - aâ - in case of the KTN black hole, whereas for a KTN naked singularity it increases with increasing nâ for a fixed aâ>0 if nâ>âcot17â . In general, the asymmetry of shadow shape increases if the central dark object in M87 is a KTN/Kerr naked singularity instead of a KTN/Kerr black hole. We find that a non-zero gravitomagnetic monopole is still compatible with the current EHT observations, in which case the upper limit of nâ cannot be greater than 1.1, i.e., nââ²1.1 for the prograde rotation (aâ>0), and the lower limit of nâ cannot be less than â1.1, i.e., nââ³â1.1 for the retrograde rotation (aâ<0). Moreover, if the circularity of the shadow can be measured on a precision of â²1
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