Observations show more disk galaxies than theory allows

(ORDO NEWS) — The Standard Cosmological Model describes the formation and evolution of the universe since the Big Bang. The new work simulated the evolution of galaxies in accordance with this model and found significant discrepancies with real observations.

Most of the galaxies visible from Earth are flat disks with a thickened central part. According to the Standard Cosmological Model, however, such disks should form quite rarely. The fact is that in this model, each galaxy is surrounded by a halo of dark matter.

This halo is invisible, but has a powerful gravitational effect on nearby galaxies because it is massive. “That’s why we keep seeing mergers between galaxies in the ‘model universe’,” explains University of Bonn professor Dr. Pavel Kroupa.

These collisions entail two types of consequences. First, the penetration of galaxies into each other leads to a distortion of the shape of the disks. Secondly, the total angular momentum of a new galaxy formed as a result of the merger decreases.

In other words, there is a decrease in the speed of rotation of the galaxy. Typically, the rotational movement causes the formation of a new disk as a result of the action of centrifugal forces. However, if the angular momentum is too small, the disk does not form at all.

In their new study, Kroupa and his team simulated the evolution of the universe on a supercomputer to the present day, according to the Standard Cosmological Model, and then compared the resulting set of galaxies with real observations. As a result, a significant discrepancy between forecasts and reality was found.

In the real Universe, there were many more disk galaxies than the theory predicted. However, even on modern supercomputers, simulation resolution remains limited.

Therefore, there is a possibility that the estimate of the number of disk galaxies forming in accordance with the Standard Model turned out to be underestimated. However, taking into account this factor can only somewhat reduce the discrepancy, but not eliminate it, the authors emphasize.

According to the authors, their results testify in favor of the well-known MOND hypothesis, which excludes the concept of dark matter.

According to this scenario, galaxies do not grow by merging with each other, but are formed by condensation of rotating gas clouds. Collisions between formed galaxies in this hypothesis are very rare, the authors explained.

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