John Tonry

Astronomers have discovered a close pair of stars whose orbital dance is speeding up year after year. These are white dwarfs — superdense, cooled remnants of stars, roughly the size of Earth, where matter is compressed to a degenerate state.

If a supermassive black hole lives at the center of a galaxy, it heats the infalling gas to incredible temperatures. That gas glows, and we see it as a quasar — the brightest beacon in the universe. But how do you measure the size of the light source itself?