Answer Happy

For the first two targets of the Event Horizon Telescope, astronomers selected Sag A* in the Milky Way, and the central black hole in galaxy M87. Why did astronomers choose these two distant candidates, when we know of black holes far closer to Earth? Select one: a. Because the black holes closer to Earth are shrouded in galactic dust, and the radio waves used to observe them are strongly absorbed. Ob. Because these distant black holes are so massive, and even at great distances, the angular size of their event horizons appears larger. oc. Because nearby black holes are almost always in binary systems, and this makes the radio light from these systems impossible to observe. d. Because only supermassive black holes are massive enough to have a true event horizon.