Black hole shadow with a cosmological constant for cosmological observers. (arXiv:1905.07378v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Firouzjaee_J/0/1/0/all/0/1">Javad T. Firouzjaee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Allahyari_A/0/1/0/all/0/1">Alireza Allahyari</a>
We investigate the effect cosmological constant on the angular size of a
black hole shadow. It is known that the cosmological acceleration which is
created by a cosmological constant changes the angular size of the black hole
shadow for static observers. However, the shadow size must be calculated for
the appropriate cosmological observes. We calculate the angular size of the
shadow seen by cosmological comoving observers by projecting the shadow angle
to this observer rest frame. We show that the shadow size tends to zero as the
observer approaches the cosmological horizon. We estimate the angular size of
the shadow for a typical supermassive black hole, e.g M87. It is found that the
angular radius of the shadow for cosmological observers and static observers is
approximately the same.
We investigate the effect cosmological constant on the angular size of a
black hole shadow. It is known that the cosmological acceleration which is
created by a cosmological constant changes the angular size of the black hole
shadow for static observers. However, the shadow size must be calculated for
the appropriate cosmological observes. We calculate the angular size of the
shadow seen by cosmological comoving observers by projecting the shadow angle
to this observer rest frame. We show that the shadow size tends to zero as the
observer approaches the cosmological horizon. We estimate the angular size of
the shadow for a typical supermassive black hole, e.g M87. It is found that the
angular radius of the shadow for cosmological observers and static observers is
approximately the same.
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