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#### The fingerprints of black holes-shadows and their degeneracies

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1710.02402.pdf

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CQG_AccMan.pdf

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##### Citation

Mars, M., Paganini, C., & Oancea, M. A. (2018). The fingerprints of black holes-shadows
and their degeneracies.* Classical and quantum gravity,* *35*(2):
025005. doi:10.1088/1361-6382/aa97ff.

Cite as: https://hdl.handle.net/11858/00-001M-0000-002E-86F7-4

##### Abstract

We show that, away from the axis of symmetry, no continuous degeneration

exists between the shadows of observers at any point in the exterior region of

any Kerr-Newman black hole spacetime of unit mass. Therefore, except possibly

for discrete changes, an observer can, by measuring the black holes shadow,

determine the angular momentum and the charge of the black hole under

observation, as well as the observer's radial position and angle of elevation

above the equatorial plane. Furthermore, his/her relative velocity compared to

a standard observer can also be measured. On the other hand, the black hole

shadow does not allow for a full parameter resolution in the case of a

Kerr-Newman-Taub-NUT black hole, as a continuous degeneration relating specific

angular momentum, electric charge, NUT charge and elevation angle exists in

this case.

exists between the shadows of observers at any point in the exterior region of

any Kerr-Newman black hole spacetime of unit mass. Therefore, except possibly

for discrete changes, an observer can, by measuring the black holes shadow,

determine the angular momentum and the charge of the black hole under

observation, as well as the observer's radial position and angle of elevation

above the equatorial plane. Furthermore, his/her relative velocity compared to

a standard observer can also be measured. On the other hand, the black hole

shadow does not allow for a full parameter resolution in the case of a

Kerr-Newman-Taub-NUT black hole, as a continuous degeneration relating specific

angular momentum, electric charge, NUT charge and elevation angle exists in

this case.