Abstract
AbstractWe examine the possibility for the existence of gravitomagnetic monopole ($$n_*$$
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 $$|n_*|$$
|
n
∗
|
for a fixed Kerr parameter $$|a_*|$$
|
a
∗
|
in case of the KTN black hole, whereas for a KTN naked singularity it increases with increasing $$n_*$$
n
∗
for a fixed $$a_* > 0$$
a
∗
>
0
if $$n_* > -\cot 17^{\circ }$$
n
∗
>
-
cot
17
∘
. 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 $$n_*$$
n
∗
cannot be greater than 1.1, i.e., $$n_* \lesssim 1.1$$
n
∗
≲
1.1
for the prograde rotation ($$a_* > 0$$
a
∗
>
0
), and the lower limit of $$n_*$$
n
∗
cannot be less than $$-1.1$$
-
1.1
, i.e., $$ n_* \gtrsim -1.1$$
n
∗
≳
-
1.1
for the retrograde rotation ($$a_* < 0$$
a
∗
<
0
). Moreover, if the circularity of the shadow can be measured on a precision of $$\lesssim 1\%$$
≲
1
%
, the Kerr and KTN naked singularities can be falsified for M87*.
Funder
National Natural Science Foundation of China
Strategic Priority Program of the Chinese Academy of Sciences
National Key Program for Science and Technology Research and Development
China Postdoctoral Science Foundation
Publisher
Springer Science and Business Media LLC
Subject
Physics and Astronomy (miscellaneous),Engineering (miscellaneous)
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