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Paper IPM / Astronomy / 16779  


Abstract:  
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 KerrTaubNUT (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 nonzero 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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