Scientists discover ‘alternative’ dwarf galaxy challenges classic dwarf formation theory

In the early hours of November 26th, the international scientific journal Nature Astronomy published an important finding by our astronomers: They found that there was a special class of dwarf galaxies in the adjacent universe, which, within a radius of tens of thousands of light-years, were made up mainly of heavy matter, which was only a small part of it. This contradicts the theoretical prediction of dwarf galaxy formation under the current standard cosmology model, thus questioning the nature of cold and dark matter and challenging the classical dwarf galaxy formation theory. The work was led by the scientific research team of the National Observatory of the Chinese Academy of Sciences, and was carried out jointly by the scientific research teams of Peking University and Tsinghua University.

Scientists discover 'alternative' dwarf galaxy challenges classic dwarf formation theory

Figure 1: Dark matter dominates the formation of structures, and galaxies form and evolve in dark halos dominated by dark matter. The illustration shows the formation of a structure simulated by a supercomputer with a side length of about 200 million light-years. The changes in density from black, green, yellow, pink to white show the low to high density, and the halo corresponds to the high density area of white.

Under the standard cosmological model, dominated by dark energy and cold and dark matter, galaxies form and evolve in dark matter halos. In large-mass systems, the proportion of heavy sons can reach the average of the universe, which decreases rapidly as the mass of the halo decreases. Because of the weak ability of low-mass systems to bind heavy sons, it is generally assumed that the content of the weight is very small relative to dark matter in the system of dwarf galaxies, which is also confirmed in the satellite galaxies of our Milky Way and this cluster. Unlike large galaxies, these satellite galaxies are dominated by dark matter, even within a half-light radius. Unfortunately, because dwarf galaxies have very dark luminal light, current research on the dynamics of dwarf galaxies can only be confined to very close-neighbored universes, mostly within or around the clusters of galaxies.

Scientists discover 'alternative' dwarf galaxy challenges classic dwarf formation theory

Figure 2: One of the newly discovered strange dwarf galaxies, UGC7920. Photo credit: DECaLS-DR8

The team, led by Researcher Guo Wei of the National Observatory of the Chinese Academy of Sciences, combined with the results of Sloan’s Digital Optical Survey and Arecibo’s Neutral Hydrogen Survey, conducted the first statistical study of the dynamics of the dwarf galaxy outside the cluster. They found a particular class of dwarf galaxies, unlike previous observations and numerical simulations, which are dominated by heavy matter in areas covered by HI. The neutral hydrogen-covered region is usually tens of thousands of light-years away, and in a typical dwarf galaxy system, the dark matter mass in this area is ten to several hundred times the mass of heavy matter. In particular, most of the dwarf galaxies they found were isolated systems that were not affected by the outside environment. Currently, there are no theoretical or numerical simulations in standard cosmological models that can explain the formation of such galaxies.

The discovery raises serious questions about the standard cosmological model, as well as the theory of galaxy formation under it, prompting a re-examination of the nature of dark matter, which is easier to explain in the formation of such dwarf galaxies. On the other hand, the weight ingress under extreme conditions also provides a possible explanation. Answering these questions will require further use of more advanced telescopes.

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