Question

1. Determine the diameter D of the smallest telescope needed to resolve an “invisible” gravitational lens with a mass and radius the same as Earth. Assume the lensed object (e.g., a star) is directly behind the lens and is observed at a wavelength of 500 nm. 2. Suppose the Sun turns into a black hole. Ignoring the disastrous climatic consequences that would doom the inhabitants of Earth, how large would the Sun appear in arcseconds if you could “see” its event horizon? 3. Suppose a photon with 20 = 500 nm escapes the vicinity of a solar-mass black hole. If the photon starts 2 Schwarschild radii from the center, what is the wavelength of the observed photon af at infinity?