The M87 black hole is at the centre, more or less, of an elliptical galaxy of 1 trillion or more stars. So certainly there are stars and other light emitting objects (emission nebula e.g.) in the intervening 53 million light years between earth and the black hole.
How is it that the centre of the black hole image is perfectly dark, as if it is being observed directly, with not one point of light between the black hole and earth? I appreciate that space is mostly empty, but do we really have an unobscured line of sight to a black hole in the centre of an enormous elliptical galaxy?
Does it have something to do with the type of light being observed?