Scientists are baffled by new observations from 13 million light-years away, where a group of satellites, or dwarf galaxies, orbits the much larger elliptical galaxy Centaurus A. And while this isn’t a particularly unique phenomenon, what’s struck scientists as peculiar is how the satellites’ movements do not seem to mesh with existing theories about dark matter and how it influences the movement of galaxies in the universe.
Dark matter is the term used to describe the large mass of the universe that cannot be directly observed by astronomers. Based on the lambda cold dark matter model, the material is believed to hold together the regular matter that can be observed and detected with telescopes and other instruments. According to Ars Technica, this “regular” material takes up only about 4.6 percent of the universe’s mass. However, the behavior of the dwarf galaxies orbiting Centaurus A has raised some new questions about the model and its position on dark matter, as the smaller galaxies were observed to be making their orbits on a common plane, as opposed to the random directions and angles suggested by the standard model.
Although the lambda cold dark matter model suggests that satellite galaxies should create a “more or less spherical cloud” by darting around randomly as they orbit the central galaxy, the observation documented this week in the journal Science is not completely unique. There are multiple dwarf galaxies known to orbit the Milky Way, while all but two of Andromeda’s 15 satellites have been known to orbit in the same plane. But as a report from the Daily Galaxy stated, this is the first time such “preferentially oriented” orbits have been spotted outside the Local Group, where the Milky Way is located. In all, 14 out of Centaurus A’s 16 satellites were found to be moving in the same plane while orbiting their host galaxy.
According to study author and University of California-Irvine astrophysicist Marcel Pawlowski, there’s a chance that scientists are “missing something” with regards to their existing theories on dark matter. He believes that it may be time to consider alternative models, as there could have been some missing ingredients in previous simulations or fundamental flaws in the generally accepted lambda cold dark matter model.
“The significance of this finding is that it calls into question the validity of certain cosmological models and simulations as explanations for the distribution of host and satellite galaxies in the universe.”
Proposing a major paradigm shift or revising the standard dark matter model, however, may be easier said than done. As noted in a commentary on the new study cited by Ars Technica, many astrophysicists disagree that the standard model needs to be replaced with something that could properly justify the movements of the dwarf galaxies that orbit Centaurus A.
“It would take very strong evidence of an insurmountable problem to give up on [the lambda cold dark matter model], or at least a model that looks very much like it,” said Mike Boylan-Kolchin, an astrophysicist at the University of Texas in Austin.
Further questioning the findings revealed in the new study, Boylan-Kolchin said that there’s still sufficient cause to believe the Centaurus A satellite galaxies are, just like those orbiting the Milky Way and Andromeda, a “statistical fluke,” as Ars Technica described them. He said that the dwarf galaxies orbiting Andromeda and the Milky Way in the same plane have varying ages, masses, and chemical ingredients. This is explained by the standard model, but not by alternative theories, which make no mention of separate collisions resulting in the creation of the universe’s many galaxies.
Ars Technica pointed out another possible justification behind the unusual planar movements of Centaurus A’s dwarf galaxies, stating that the dark matter filaments that dictate the movements of galaxies might be scaled about 10 to 20 times greater than the distance separating the host galaxy from Earth. With that taken into account, this could explain the planar orbits around Centaurus A as a “quirk” that doesn’t show up in model universe simulations.
With the new findings seemingly raising more questions than providing answers with regards to the mysteries of dark matter, scientists believe more research is needed to truly dispute the theories stated within the lambda cold dark matter model. According to Pawlowski, observing more distant galaxies could help “rule out any local quirks,” and possibly prove that there are other host galaxies aside from Andromeda, the Milky Way, and Centaurus A where dwarf galaxies orbit their hosts on a shared plane.