After observing a binary system of two dead stars for 20 years, astronomers have detected the very subtle effect of Einstein's hand: Frame-dragging, an outcome of General Relativity where a rapidly spinning massive object literally drags the fabric of spacetime around it, winding it up like a thread around a spindle.
Every single step of this science is bizarre and astonishing and oh-so-cool. Let's go through 'em.
The binary system is a pulsar (called PSR J1141-6545) and a white dwarf orbiting each other. A white dwarf is the leftover core of a star similar to the Sun after it dies. It sheds its outer layers, revealing the hot dense core: A ball the size of the Earth but with the mass of a star.
A pulsar is similar, but colossally more violent. It's the leftover core of a much more massive star that has exploded as a supernova. The explosion ejects the outer layers rapidly and catastrophically, while the core collapses to become a ball of neutrons maybe 20 kilometers across but even more massive than a white dwarf. We call such an object a neutron star. They sometimes emit beams of radiation from their poles, and as they spin ...