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Distant galaxies lack dark matter, study suggests

Star velocities defy expectations based on standard theory

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2:00pm, March 15, 2017
hydrogen signatures of galaxies

SLUGGISH STARS  A hydrogen signature reveals the structure of six galaxies (top, bright regions appear red) observed with the Very Large Telescope in Chile. The signature also shows the velocities (bottom) of stars in the galaxies (blue regions are moving toward the telescope; red areas, away). Stars farther from the galactic center unexpectedly appear to move more slowly than stars closer in.

Very distant galaxies have surprisingly little dark matter, the invisible stuff thought to make up the bulk of matter in the universe, new observations suggest.

Stars in the outer regions of some far-off galaxies move more slowly than stars closer to the center, indicating a lack of dark matter, astronomer Reinhard Genzel and colleagues report online March 15 in Nature. If confirmed, the result could lead astronomers to reconsider the role dark matter played in early galaxy evolution and might also offer clues to how nearby elliptical galaxies evolved.

In contrast with these distant galaxies, stars orbiting on the outskirts of the Milky Way and other nearby galaxies move too fast for their velocities to result only from the gravity of gas and stars closer to the galactic center. If visible galactic matter is embedded in a

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