Our Galaxy is a grand highway where stars race along their paths. Just as a driver gauges their speed by watching neighboring cars, astronomers determined the trajectory of the Sun from the motion of nearly 1,200 ultrafast stars. For each one, they measured the velocity along the line of sight (spectroscopy) and the shift on the sky, assembling a complete 3D picture. An unexpected twist: some of these stars are accelerated so powerfully by the central black hole that they are flung off the galactic “road” forever.

But the key is that these “runaways” reveal the invisible skeleton of the Galaxy. Their trajectories betray the pull of dark matter — the mysterious mass that doesn’t shine but holds the stars together. This method of “weighing” the cosmos was first proposed by Fritz Zwicky and Vera Rubin, who noticed that visible matter alone cannot explain the speeds of stars and galaxies.