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> Close Encounters of the Galactic Kind

JULY 2008

Close Encounters of the Galactic Kind

An array of 59 interacting galaxies
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Interacting galaxies gallery

Astronomy textbooks typically present galaxies as calm, solitary, and majestic island worlds of glittering stars. Astronomers, however, know that this is not the case. These 59 new Hubble images support the well-known idea that galaxies are dynamic and energetic. This new Hubble atlas dramatically illustrates how galaxy collisions produce a remarkable variety of intricate structures in never-before-seen detail.

When galaxies collide

Butterfly-shaped merging galaxies
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Butterfly: Two small galaxies merge


Dolphin-shaped pair of overlapping galaxies
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Leaping dolphin: Two edge-on galaxies overlap

Interacting galaxies are found throughout the universe, sometimes as dramatic collisions that trigger bursts of star formation, on other occasions as mergers that result in new galaxies. These interactions occur when gravity causes the galaxies to tug and pull on each other creating wondrous new shapes, including mergers that look like a butterfly, a leaping dolphin, an owl in flight, and even a toothbrush. They also offer a preview of our own galaxy’s fate a few billion years from now, when it merges with the nearby Andromeda Galaxy. The future resulting elliptical galaxy has already been dubbed “Milkomeda.”

Building bigger galaxies

Colliding galaxies resembling an owl in flight
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Owl in flight:
Two former disk galaxies collide

Astronomers observe about one out of a thousand galaxies in the nearby universe in the act of colliding. Galaxy interactions are short-lived, lasting a few hundred million years, while the lifespan of a typical galaxy is roughly 10 billion years. However, most, if not all galaxies, have likely undergone collisions or mergers in their past. In fact, scientists believe that is how the big galaxies we see today got started -- through the merger of smaller clusters of stars and small galaxies going back to the earliest moments of the evolution of the universe.

A toothbrush-shaped galaxy has been in a collision
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Toothbrush:
A collision gave this galaxy an odd shape

Astronomers study how gravity choreographs the motion of galaxies in the game of celestial bumper cars and try to observe them in action. These observations help astronomers understand the evolution of galaxies over time.

 

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