L. Magrini

Sometimes you find a movie ticket from three years ago in the pocket of an old jacket. You can't reconstruct the time from it, but you can figure out where the owner went. The same goes for hot subdwarfs — tiny stars in the late stages of life that shine mostly in ultraviolet. Their light is like that ticket: it tells you about the past, but reading it is tricky.

Wide binary stars are like two dancers holding hands but standing at opposite ends of the hall. Their bond is weak, and any passerby can break them apart. Astronomers found 26 such pairs and tested how tightly they hold on. It turned out that 12 pairs dance by Newton's rules: their orbits can be calculated like those of planets around the Sun. But three pairs move too fast.