Shadow of Kottler black hole in the presence of plasma for a co-moving observer

Abstract

Abstract In this paper, we discussed the shadow of a static, spherically symmetric black hole geometry in presence of a positive cosmological constant <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Λ</mml:mi> <mml:mo>&gt;</mml:mo> <mml:mn>0</mml:mn> </mml:math> . We analysed the black hole shadow both in absence and presence of plasma. Then we study the black hole shadow from the point of view of a comoving observer. We display the plots for the angular shadow size as measured by a comoving observer. The effects of the cosmological constant Λ and plasma parameter k on the angular size of the black hole shadow have been investigated in detail. Finally, by using the observed angular size of M87 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi/> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> and Sgr A <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi/> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> black hole, we constrain the value of the plasma parameter k with a specific observational value of the cosmological constant Λ (or the Hubble constant H 0 ).