Odd galaxies found that contradict theories of formation

Chinese astronomers have discovered a special population of dwarf galaxies that mainly consist of baryons with radii of up to tens of thousands of light-years, where they are expected to be dominated by dark matter.

The discovery, made by researchers from the National Astronomical Observatories of the Chinese Academy of Sciences, Peking University and Tsinghua University, was published in the latest issue of the science journal Nature Astronomy.

The finding provides observational evidence that could challenge the formation theory of dwarf galaxies in the framework of standard cosmology, and may provide new clues to the nature of dark matter, said Guo Qi, a researcher from the NAOC and head of the research team.

In standard cosmology, the universe is dominated by cold dark matter and dark energy, while baryons only occupy 4.6 percent of outer space. Galaxies form and evolve in systems dominated by dark matter.

Statistical studies beyond the Local Group, our neighborhood in the universe, however, were hampered in the past due to the extreme faintness of the dwarf galaxies.

By analyzing the data of the Arecibo Observatory and the Sloan Digital Sky Survey, the research team found 19 dwarf galaxy candidates that are dominated by baryonic masses.

This result is difficult to explain with the standard galaxy formation model, and thus encourages people to revisit the nature of dark matter, Guo said.

Further observations are required to understand the formation of these particularly baryonic-dominated dwarf galaxies, Guo added.