The Milky Way contains an estimated 200 billion stars. But that’s just the bare tip of the iceberg — the Galaxy is surrounded by vast amounts of an unknown material called dark matter. Astronomers know it exists because, dynamically, the Milky Way would fly apart if dark matter didn’t keep a gravitational lid on things. Still, astronomers would like to have a precise measure of the Galaxy’s mass to better understand how the myriad galaxies...
