Galaxies hide invisible matter
Unexpectedly fast-spinning galaxies reveal the presence of invisible dark matter, a mysterious substance making up most of the universe's mass and shaping its structure.
Galaxies spin in a way that reveals a cosmic secret: most of their mass is invisible. In the 1970s, astronomer Vera Rubin observed stars at the edges of spiral galaxies orbiting just as fast as those closer to the center. This defied expectations, as Newtonian physics predicted outer stars should slow down, much like planets further from the Sun.
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