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Paper   IPM / Astronomy / 16779
School of Astronomy
  Title:   Investigating the existence of gravitomagnetic monopole in M87*
  Author(s): 
1.  M. Ghasemi-Nodehi
2.  Chandrachur . Chakraborty
3.  Qingjuan . Yu
4.  Youjun . Lu
  Status:   Published
  Journal: Eur. Phys. J. C
  Year:  2021
  Supported by:            ipm IPM
  Abstract:
We examine the possibility for the existence of gravitomagnetic monopole (n∗) 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 - n∗ - for a fixed Kerr parameter - a∗ - in case of the KTN black hole, whereas for a KTN naked singularity it increases with increasing n∗ for a fixed a∗>0 if n∗>−cot17∘ . 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 n∗ cannot be greater than 1.1, i.e., n∗≲1.1 for the prograde rotation (a∗>0), and the lower limit of n∗ cannot be less than −1.1, i.e., n∗≳−1.1 for the retrograde rotation (a∗<0). Moreover, if the circularity of the shadow can be measured on a precision of ≲1

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