Study on black hole shadows in asymptotically de Sitter spacetimes

Previous works on black hole shadows have been primarily focused on studying shadows in asymptotically flat and anti-de Sitter space times. In the present work, we find general expressions for asymptotically de Sitter black hole shadow as seen by static and comoving observers, for any spherically symmetric black hole solution, in any space time dimension in generic theories of gravity. As test cases, we use the derived general expressions to study the shadow of three different black hole solutions: the four dimensional Reissner-Nordstrom de Sitter black hole, the recently proposed four dimensional Gauss Bonnet de Sitter black hole and the five dimensional Gauss Bonnet de Sitter black hole.