Too many disk galaxies than theory allows

Date:
February 4, 2022
Source:
University of Bonn
Summary:
The Standard Model of Cosmology describes how the universe came
into being according to the view of most physicists. Researchers
have now studied the evolution of galaxies within this model,
finding considerable discrepancies with actual observations.



FULL STORY ==========================================================================
The Standard Model of Cosmology describes how the universe came into being according to the view of most physicists. Researchers at the University of
Bonn have now studied the evolution of galaxies within this model, finding considerable discrepancies with actual observations. The University of St.

Andrews in Scotland and Charles University in the Czech Republic were
also involved in the study. The results have now been published in the Astrophysical Journal.


==========================================================================
Most galaxies visible from Earth resemble a flat disk with a thickened
center.

They are therefore similar to the sports equipment of a discus thrower.

According to the Standard Model of Cosmology, however, such disks
should form rather rarely. This is because in the model, every galaxy is surrounded by a halo of dark matter. This halo is invisible, but exerts a strong gravitational pull on nearby galaxies due to its mass. "That's why
we keep seeing galaxies merging with each other in the model universe," explains Prof. Dr. Pavel Kroupa of the Helmholtz Institute for Radiation
and Nuclear Physics at the University of Bonn.

This crash has two effects, the physicist explains: "First, the galaxies penetrate in the process, destroying the disk shape. Second, it reduces
the angular momentum of the new galaxy created by the merger." Put simply,
this greatly decreases its rotational speed. The rotating motion normally ensures that the centrifugal forces acting during this process cause a
new disk to form. However, if the angular momentum is too small, a new
disk will not form at all.

Large discrepancy between prediction and reality In the current study,
Kroupa's doctoral student, Moritz Haslbauer, led an international research group to investigate the evolution of the universe using the latest supercomputer simulations. The calculations are based on the Standard
Model of Cosmology; they show which galaxies should have formed by today
if this theory were correct. The researchers then compared their results
with what is currently probably the most accurate observational data of
the real Universe visible from Earth.

"Here we encountered a significant discrepancy between prediction and
reality," Haslbauer says: "There are apparently significantly more flat
disk galaxies than can be explained by theory." However, the resolution
of the simulations is limited even on today's supercomputers. It may
therefore be that the number of disk galaxies that would form in the
Standard Model of Cosmology has been underestimated. "However, even if we
take this effect into account, there remains a serious difference between theory and observation that cannot be remedied," Haslbauer points out.

The situation is different for an alternative to the Standard Model,
which dispenses with dark matter. According to the so-called MOND theory
(the acronym stands for "MilgrOmiaN Dynamics), galaxies do not grow
by merging with each other. Instead, they are formed from rotating
gas clouds that become more and more condensed. In a MOND universe,
galaxies also grow by absorbing gas from their surroundings. However,
mergers of full-grown galaxies are rare in MOND.

"Our research group in Bonn and Prague has uniquely developed the methods
to do calculations in this alternative theory," says Kroupa, who is
also a member of the Transdisciplinary Research Units "Modelling" and
"Matter" at the University of Bonn. "MOND's predictions are consistent
with what we actually see." Challenge for the Standard Model However,
the exact mechanisms of galaxy growth are not yet fully understood,
even with MOND. Additionally, in MOND, Newton's laws of gravity do
not apply under certain circumstances, but need to be replaced by the
correct ones. This would have far-reaching consequences for other areas
of physics. "Nevertheless, the MOND theory solves all known extragalactic cosmological problems despite being originally formulated to address
galaxies only," says Dr. Indranil Banik, who was involved in this
research. "Our study proves that young physicists today still have the opportunity to make significant contributions to fundamental physics,"
Kroupa adds.

========================================================================== Story Source: Materials provided by University_of_Bonn. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Moritz Haslbauer, Indranil Banik, Pavel Kroupa, Nils Wittenburg,
Behnam
Javanmardi. The High Fraction of Thin Disk Galaxies Continues to
Challenge LCDM Cosmology. The Astrophysical Journal, 2022; 925
(2): 183 DOI: 10.3847/1538-4357/ac46ac ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220204123542.htm

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