Distant galaxies and the true nature of dark matter

Date:
February 11, 2022
Source:
Scuola Internazionale Superiore di Studi Avanzati
Summary:
In conflict with the current prevailing theory used to describe the
universe, a new study suggests the existence of a direct interaction
between the elementary particles that make up the dark matter halo
and those that make up ordinary matter.



FULL STORY ==========================================================================
At the centre of spiral galaxies -- those near to us but also those
billions of light-years away -- there is a vast spherical region made up
of dark matter particles. This region has two defining characteristics:
a density that is constant out to a certain radius that amazingly expands
over time, while the density decreases. This suggests the existence
of a direct interaction between the elementary particles that make up
the dark matter halo and those that make up ordinary matter -- protons, electrons, neutrons, and photons. We anticipate that this hypothesis is
in direct conflict with the current prevailing theory used to describe
the universe -- known as Lambda-Cold Dark Matter -- which posits that
particles of cold dark matter are inert and do not interact with any
other particle except gravitationally.


========================================================================== These important findings have been reported in a new study, recently
published in the prestigious Astronomy and Astrophysics journal,
that studied a large number of distant galaxies, some seven billion
light-years away. The study, conducted by Gauri Sharma and Paolo
Salucci from SISSA, together with Glen Van de Ven from the University
of Vienna, took a new look at one of the greatest mysteries of modern
physics. According to the authors, this new research represents a step
forward in our understanding of dark matter, the elusive element in our universe which has been theorised based on its demonstrable effects on
heavenly bodies, but which is yet to be directly proven. This is despite
any number of targeted astrophysical observations and experiments set
up for the purpose in dedicated underground laboratories.

Studying dark matter in distant galaxies Dark matter makes up
approximately 84% of the mass in the cosmos: "Its dominant presence
throughout the galaxies arises from the fact that the stars and hydrogen
gas are moving as if governed by an invisible element" explains Gauri
Sharma. Up until now, attempts to study it have focused on galaxies near
to our own: "In this study, however," she explains, "for the first time,
we were seeking to observe and determine the distribution of the mass
of spiral galaxies with the same morphology of those nearby, but much
further away and therefore earlier by some seven billion years. The
idea is essentially that these progenitors of spiral galaxies like
our own could offer fundamental clues into the nature of the particle
at the heart of the mystery of dark matter." Paolo Salucci adds: "By
studying the movement of stars in approximately 300 distant galaxies, we discovered that these objects also had a halo of dark matter, and that,
by starting out from the centre of a galaxy, this halo effectively has
a region in which its density is constant." This trait had already been observed in studies examining nearby galaxies, some of which were also
the work of SISSA.

The new research has revealed, however, that this central region had
something that was wholly unexpected within the context of the so-called "standard model of cosmology." Sharma says that "as a result of the
contrast between the properties of nearby and distant spiral galaxies --
that is, between today's galaxies and their forebears from seven billion
years earlier, we could see that not only is there an unexplained region
with a constant density of dark matter, but also that its dimensions
increase over time as if being subjected to a process of ongoing expansion
and dilution." This evidence is very difficult to be explained if the
dark matter particles did not interact, as posited in the Lambda-CDM
model. "In the research we recently published," says Sharma, "we offer
evidence of direct interaction between dark matter and ordinary matter,
that over time slowly builds up a region of consistent density from the
centre of the galaxy outwards." But there's more.

A slow yet inexorable process "Amazingly, the above region with constant density expands over time. It's a very slow process, but one that is inexorable" states Salucci. One possible explanation? "The simplest is
that, in the beginning, when the galaxy was formed, the distribution
of dark matter in the spherical halo was as predicted by the Lambda-CDM
theory, with a density peak in the centre. Later on, the galactic disc
that characterises spiral galaxies is formed, surrounded by a halo of
extremely dense dark matter particles. As time passed, the effect of the interaction that we have posited meant that the particles were captured
by the stars or expelled into the outer reaches of the galaxy." This
process would create a spherical region of consistent density within the
dark matter halo, with dimensions that increase proportionately over time
and finally reach those of the galactic stellar disc, as described in
the article in "Astronomy and Astrophysics." "The results of the study
pose important questions for alternative scenarios that describe dark
matter particles (aside from Lambda- CDM), such as Warm Dark Matter, Self-Interacting Dark Matter and Ultra Light Dark Matter" says Sharma.

"These models must also account for the clear time evolution registered
of the above region. The properties of very distant galaxies in
space and time offer cosmologists a genuine gateway to understanding
the mysteries of dark matter." It is interesting to note, "that,
in line with Nietzsche's philosophy, the truth of this mystery may be
revealed not by detailing the most beautiful scenario -- the one that
is mathematically most elegant, simple and anticipated as an expansion
of long-verified theories -- but rather through an "ugly" scenario
determined by an inelegant and complicated observational phenomenology,
from a neglected physical theory that is completely unrelated to that
which is familiar to us," says Salucci.

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


========================================================================== Journal Reference:
1. G. Sharma, P. Salucci, G. van de Ven. Observational evidence
of evolving
dark matter profiles since z 1. Astronomy & Astrophysics, 2022;
DOI: 10.1051/0004-6361/202141822 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220211102628.htm

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