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 cloud of invisible dark matter, though, gravity from the invisible matter can explain the high stellar velocities. Using stars’ orbital velocities in nearby galaxies as a reference, astronomers expected that stars in galaxies farther away would behave similarly. “Turns out that is not the case,” says study coauthor Stijn Wuyts of the University of Bath in England.
The plot of stars’ velocities relative to their distances from a galaxy’s center is called a galactic rotation curve. In the new paper (and others posted online at arXiv.org), the team presents rotation curves measured with the Very Large Telescope in Chile for more than 100 distant galaxies, some seen as they were just a few billion years after the Big Bang, 13.8 billion years ago.
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 cloud of invisible dark matter, though, gravity from the invisible matter can explain the high stellar velocities. Using stars’ orbital velocities in nearby galaxies as a reference, astronomers expected that stars in galaxies farther away would behave similarly. “Turns out that is not the case,” says study coauthor Stijn Wuyts of the University of Bath in England.
The plot of stars’ velocities relative to their distances from a galaxy’s center is called a galactic rotation curve. In the new paper (and others posted online at arXiv.org), the team presents rotation curves measured with the Very Large Telescope in Chile for more than 100 distant galaxies, some seen as they were just a few billion years after the Big Bang, 13.8 billion years ago.
