black hole, echo mapping, galaxies, nasa, outer space, supermassive black holes

‘Echo Mapping’ in Faraway Galaxies Could Measure Vast Cosmic Distances

When you look up at the night sky at the galaxies, how do you know whether the specks of light that you see are bright and far away, or relatively faint and close by? One way to find out is to compare how much light the object actually emits to how bright it appears. The ...