A collection of Hubble Space Telescope images shows distant supernovas, the death explosions of massive stars. The top photos show each region before the explosion. The bottom row shows the explosions' aftermaths

According to NASA, "Hubble played a key role in discovering that a mysterious form of energy called dark energy is acting like a cosmic gas pedal, accelerating the universe's expansion rate. Dark energy shoves galaxies away from each other at ever-increasing speeds and works in opposition to gravity." Hubble's observations of supernovas helped reveal that the mysterious energy is a constant presence in the universe.

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