June 11, 2014
Neighboring Satellite Dwarf Galaxies Do Not Fit The Standard Model
Lawrence LeBlond for redOrbit.com - Your Universe Online
An international team of scientists have found that dwarf satellite galaxies that orbit the Milky Way and neighboring Andromeda galaxy defy the standard model of galaxy formation. As well, recent attempts to fit them into the model have been flawed, raising questions about the accuracy of the standard model of cosmology, which has been the long accepted concept for the origin and evolution of the universe.
In a paper to be published in the Monthly Notices of the Royal Astronomical Society, the team explains that the standard model – also known as the lambda cold dark matter model – suggests that satellite dwarf galaxies around the Milky Way and Andromeda are expected to behave a certain way.
Study lead author Marcel Pawlowski, a postdoctoral researcher in the astronomy department at Case Western Reserve University, noted that satellite dwarf galaxies are expected to form in halos of dark matter, are widely distributed and move in random directions.
"But what astronomers see is different," Pawlowski said in a statement. "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."
Dwarf galaxies and their star clusters are found in the Magellanic plane, or Vast Polar Structure within the Milky Way. In Andromeda, about half of such galaxies and stars are in the Great Plane of Andromeda.
The study team, consisting of more than a dozen scientists from six countries, examined three recent papers that concluded the planar distributions of galaxies fit the standard model.
"When we compared simulations using their data to what is observed by astronomers, we found a very substantial mismatch," Pawlowski said.
"Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies," added David Merritt, professor of astrophysics at Rochester Institute of Technology.
"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," Merritt said. "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."
With computers, the research team simulated mock observations of thousands of Milky Way galaxies using the same data from the three analyzed research papers. They could only find one of a few thousand simulations that matched what astronomers actually observe around the Milky Way.
"But we also have Andromeda," Pawlowski said in a statement. "The chance to have two galaxies with such huge disks of satellite galaxies is less than one in 100,000."
When the team corrected the flaws found in the three papers, they could not reproduce the findings made in those studies.
"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," explained Merritt.
"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 coauthor Benoit Famaey, a senior research associate at the University of Strasbourg in France.
Dark matter is thought to be an as-yet undetected matter that provides galaxies with enough mass to prevent the speed of their rotation from pulling them apart. If present, the invisible cloud of matter would be extremely unlikely to result in the planar structures seen, explain the team.
The authors, which are among an elite but growing body of scientists who believe the standard model is flawed, suggest there is an alternative and older explanation for the satellite dwarf galaxies: a collision between two galaxies. A collision may have ripped material from the galaxies and thrown it a great distance, much like tides on Earth. Thus, the resulting tidal dwarf galaxies are formed from the debris.
"Standard galaxies must contain dark matter, but tidal galaxies cannot contain dark matter," said Pavel Kroupa, a co-author of the study and a professor at the University of Bonn in Germany. "There's a very serious conflict, and the repercussion is we do not seem to have the correct theory of gravity."
The group plans to continue its study of tidal dwarf galaxies and whether another alternative standard model – modified gravity – fits with what they observe. While science may initially balk at the idea of a new alternative standard model, it has also historically embraced challenges to accepted theories.
"When you have a clear contradiction like this, you ought to focus on it," said Merritt. "This is how progress in science is made."
FOR THE KINDLE: The History of Space Exploration: redOrbit Press