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Study says early galaxies had less dark matter

rotating disc galaxies A schematic illustration showing how differences in the distribution of dark matter (red) alter the spin rates of modern-day spiral galaxies (left) and spiral galaxies from the early universe (right). Modern spiral galaxies tend to spin faster than their counterparts in the distant, earlier universe due to greater concentrations of dark matter near their centers. Credit: ESO/L. Calçada

New observations of young, distant galaxies reveal that dark matter wielded surprisingly little influence in much of the early universe.

According to EarthSky, a new study conducted using the European Southern Observatory (ESO) Very Large Telescope in Chile has shown that dark matter affected the movement of the universe’s first galaxies less than expected.

Dark matter is thought to comprise the bulk of the universe’s mass, although it is not directly detectable.  Scientists theorize that dark matter exists to explain the motion of galaxies, which move in a way that cannot be explained by the mass of their visible matter alone.

The new study finds that distant – and therefore younger to the Earth-based observer – galaxies show a slower rotation rate at their outer edges than do older galaxies.

Dark matter is used to explain why stars at the edges of local galaxies, such as Andromeda, move as fast as stars at the galactic center.  The slower movement of outer stars in ancient galaxies suggests that dark matter was much less influential in the early universe.

The research team looked at six huge, star-forming galaxies dating from a period of widespread galaxy formation that occurred about 10 billion years ago.

“Surprisingly, the rotation velocities are not constant, but decrease further out in the galaxies,” Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics said in a statement.  “There are probably two causes for this. Firstly, most of these early massive galaxies are strongly dominated by normal matter, with dark matter playing a much smaller role than in the Local Universe. Secondly, these early discs were much more turbulent than the spiral galaxies we see in our cosmic neighborhood.”

ESO scientists suggest that dark matter in the early universe was too spread out to have the influence it has today.  Over billions of years, dark matter could have coalesced around galaxies to cause the movement patterns observed in local galaxies.

The study was published in the journal Nature.

Kathy Fey

Kathy Fey

Staff Writer
Kathy Fey is a freelance writer with a creative writing degree from Mount Holyoke College. She is an active blogger and erstwhile facilitator of science and engineering programs for children.
About Kathy Fey (623 Articles)
Kathy Fey is a freelance writer with a creative writing degree from Mount Holyoke College. She is an active blogger and erstwhile facilitator of science and engineering programs for children.