Dwarf Galaxies Could Put a New Spin on Ideas of Dark Matter

Dark matter may be the source of much of the unseen “stuff” in the Universe, but cosmological models surrounding it may need to be revised, according to a new study published in the journal Science. If these findings are confirmed, this discovery could radically change the known laws of physics surrounding the mysterious mass permeating the Universe.

Dwarf galaxies are relatively small families of stars orbiting larger galaxies. According to current thinking, these companions should be found in random locations around their parent bodies. However, observations of these bodies, seen orbiting the galaxy Centaurus A, show dwarf galaxies orbiting in regular planes around their larger companion. Of the dwarf galaxies studied, 14 of 16 showed coherent movement, revolving around a plane set at right angles to the disc of stars within the main body.

“Coherent movement seems to be a universal phenomenon that demands new explanations,” said Oliver Müller from the physics department at the University of Basel in Switzerland.

The Milky Way Galaxy, in which our solar system is located, has its own family of dwarf galaxies, as does our galactic neighbor, Andromeda. Several years ago, astronomers noticed these smaller companions following regular planes of travel as they revolve around their larger companion. Since this observation did not match with predictions regarding the behavior of stars interacting with dark matter, most researchers believed our own galactic family to be an anomaly.

Oliver Müller and his team found, however, that other dwarf galaxies also exhibit similar behavior, suggesting similar movements may be more common than believed. Current models for the behavior of dark matter suggest that only one in 200 dwarf galaxies should behave in the manner seen around the Milky Way and Centaurus A.

Centaurus A and attendant Dwarf Galaxies
Centaurus A surrounded by dwarf galaxies. Seen in the center is a lane of dark dust. University of Basel / Christian Wolf and SkyMapper Team/Australian National University

“This is inconsistent with more than 99% of comparable galaxies in simulations. Centaurus A, the Milky Way, and Andromeda all have highly statistically unlikely satellite systems. This observational evidence suggests that something is wrong with standard cosmological simulations,” reported the researchers in the article examining the study.

Although traditional thinking on the nature of galaxy formation is unable to explain these observations, it is possible that dwarf galaxies may form from the collision of pairs of galaxies, releasing stars which gather together into these smaller galactic bodies.

Dark matter cannot be seen, as it does not reflect or emit energy, giving the mysterious “stuff” its name. However, it has a significant gravitational effect, containing more than five times as much mass as all the regular matter in the Universe. It was first observed between galaxies by Fritz Zwicky in 1933, and later confirmed within galaxies by Vera Rubin working at Kitt Peak Observatory outside Tucson, Arizona.

The telescope at Kitt Peak Observatory used by Vera Rubin in her studies of galaxies.
The telescope at Kitt Peak observatory where Vera Rubin discovered the effects of dark matter between stars in galaxies. Photo by James Maynard/The Cosmic Companion, released to Creative Commons – Reuse permitted with proper attribution.

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