According to a study led by Dr Marcel Pawlowski of Case Western Reserve University in Ohio, dwarf galaxies that orbit our Milky Way Galaxy and the Andromeda Galaxy defy the accepted model of galaxy formation. The study raises questions about the accuracy of the standard model of cosmology, which is the widely accepted paradigm for the origin and evolution of the Universe.
The theory says that satellite dwarf galaxies in the Milky Way and Andromeda are expected to behave a certain way – the galaxies would form in halos of dark matter, be widely distributed and would have to move in random directions.
“The model predicts that dwarf galaxies should form inside of small clumps of dark matter and that these clumps should be distributed randomly about their parent galaxy,” Prof David Merritt of Rochester Institute of Technology, a co-author of the study accepted for publication in the Monthly Notices of the Royal Astronomical Society (arXiv pre-print).
“But what is observed is very different. The dwarf galaxies belonging to the Milky Way and Andromeda are seen to be orbiting in huge, thin disk-like structures.”
In the Milky Way, the dwarf galaxies and accompanying star clusters and streams of stars are in what’s called the Magellanic plane, or what the astronomers call the Vast Polar Structure; and in Andromeda, half of the satellites are in the Great Plane of Andromeda.
“We see the satellite galaxies are in a huge disk and moving in the same direction within this disk, like the planets in our Solar System moving in a thin plane in one direction around the Sun. That’s unexpected and could be a real problem,” Dr Pawlowski added.
The review study critiques three recent papers by different international teams that concluded the planar distributions of galaxies fit the standard model. The critique found ‘serious issues’ with all three studies.
“When we compared simulations using their data to what is observed by astronomers, we found a very substantial mismatch,” Dr Pawlowski said.
Prof Merritt added: “the earlier papers found structures in the simulations that no one would say really looked very much like the observed planar structures.”
“Either the selection of model satellites is different from that of the observed ones, or an incomplete set of observational constraints has been considered, or the observed satellite distribution is inconsistent with basic assumptions. Once these issues have been addressed, the conclusions are different: features like the observed planar structures are very rare,” the authors said.
“The standard model contains various putative ingredients— such as dark matter and dark energy —which were introduced because the model wasn’t consistent with observations,” said study co-author Dr Benoit Famaey from the University of Strasbourg, France.
The authors of this study are among a small but growing number of astrophysicists who find the standard model fails to replicate what’s observed and therefore they seek alternatives.
They suggest an alternative and older explanation for the satellite dwarf galaxies: an ancient collision between two large galaxies.
The collision may have ripped material from the galaxies and thrown it a great distance, much like tides on Earth. The resulting tidal dwarf galaxies are formed from the debris.
The scientists will continue to study these tidal dwarf galaxies and the clues they may reveal about galaxy formation.
Marcel S. Pawlowski et al. 2014. Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies. MNRAS, accepted for publication; arXiv: 1406.1799