How do astronomers know a galaxy has merged with another galaxy in the past?
Quick Answer
They look for streams of stars, disturbed shapes, unusual star motions, and leftover gas or shells. These are the fossil traces of ancient collisions.
The Full Story
Galaxy mergers leave signatures that can remain visible for billions of years. Astronomers find tidal streams, loops, shells, and warped disks that indicate one galaxy has torn apart another. They also use stellar chemistry and motion patterns to identify groups of stars with a common origin. The Milky Way contains several such remnants, including evidence from the Gaia-Enceladus event and the Sagittarius dwarf galaxy. These clues show that galaxies grow by swallowing smaller systems over cosmic time.
Key Facts
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Suggested video title for this topic:
"The cosmic scars left by galaxy collisions"
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