https://doi.org/10.1140/epjc/s10052-021-09696-3
Regular Article - Theoretical Physics
Investigating the existence of gravitomagnetic monopole in M87*
1
National Astronomical Observatories, Chinese Academy of Sciences, 100101, Beijing, China
2
School of Astronomy, Institute for Research in Fundamental Sciences, 19395-5531, Tehran, Iran
3
Kavli Institute for Astronomy and Astrophysics, Peking University, 100871, Beijing, China
4
Depatment of Physics, Indian Institute of Science, 560012, Bengaluru, India
5
School of Astronomy and Space Science, University of Chinese Academy of Sciences, 100049, Beijing, China
Received:
10
August
2021
Accepted:
28
September
2021
Published online:
23
October
2021
We examine the possibility for the existence of gravitomagnetic monopole (
) 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 
for a fixed Kerr parameter 
in case of the KTN black hole, whereas for a KTN naked singularity it increases with increasing for a fixed 
if 
. 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 cannot be greater than 1.1, i.e., 
for the prograde rotation (), and the lower limit of cannot be less than 
, i.e., 
for the retrograde rotation (
). Moreover, if the circularity of the shadow can be measured on a precision of 
, the Kerr and KTN naked singularities can be falsified for M87*.
© The Author(s) 2021
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