For many years, astrophysicists have theorized that an invisible material they call “dark matter” makes up the majority of the universe’s mass. Any behavior of objects in the universe that can’t be explained by ordinary mass — such as how galaxies rotate in space — could be due to the gravitational effects dark matter.
But now, a bold new theory from European researchers suggests a startling alternative: the strange behavior of galaxies could be due to the combined mass of untold zillions of photons, each of which has just a tiny bit of mass.
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