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EI2GYB > ASTRO 10.11.25 14:11l 91 Lines 5372 Bytes #47 (0) @ WW
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Subj: Dwarf Galaxies May Hold the Answers to the Debate on Dark M
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Dwarf Galaxies May Hold the Answers to the Debate on Dark Matter
Dark Matter is one of the tenacious mysteries facing astronomers and
cosmologists today. This theoretical mass was proposed in the 1960s as a way to
explain the rotational curves of galaxies, which indicated that they had
greater mass than their stellar populations implied. Despite decades of
research and observation, scientists have yet to find any direct evidence of
this mysterious, invisible mass or what it is composed of. There are many
theories, ranging from weakly interacting massive particles (WIMPs) to
extremely low mass particles (axions).
Fortunately, we live in an era when the frontiers of astronomy are constantly
being pushed and new discoveries are being made all the time. In a recent
study, an international team of researchers led by the Leibniz Institute for
Astrophysics Potsdam (AIP) has shed light on this decades-old debate by
analyzing stellar velocities from 12 of the smallest and faintest galaxies in
the Universe. The team found that the internal gravitational fields of these
galaxies could not be explained by visible matter alone, further bolstering the
case for Dark Matter.
The team was led by researchers from the AIP, and included members from the
Institute for Physics and Astronomy at Potsdam University, University of
Surrey, the University of Bath, the School of Astronomy and Space Science at
Nanjing University, the Institute of Astrophysics and Space Sciences at the
University of Porto, the Leiden Observatory at Leiden University, and the Lund
Observatory at Lund University. The paper describing their findings recently
appeared in the journal Astronomy & Astrophysics.
For decades, scientists have debated the existence of Dark Matter (DM). On the
one hand, its existence is inferred from observations and our understanding of
gravity (as described by Einstein's Theory of General Relativity). On the other
hand, there is a lack of direct evidence, which has led to alternative
theories, such as Modified Newtonian Dynamics (MOND). This theory emerged in
the 1980s and posits that the laws of gravity change at very low accelerations
(i.e., on very large distance scales).
In addition, astronomers have long held that there is a simple relationship
between the amount of visible (baryonic) matter a galaxy contains and the
gravitational force it exerts - known as the Radial Acceleration Relation
(RAR). While this theory certainly applies to larger systems, the new study
suggests that it breaks down in the smallest galaxies. Upon examining 12 dwarf
galaxies and inferring their mass distributions, they found that MOND
predictions failed to reproduce the observed behavior, proving that their
gravitational fields could not be explained by visible matter alone.
They then compared their results with theoretical models that assume the
presence of dark matter haloes around galaxies using the DiRAC National
Supercomputer facility. The results of these simulations provided a much better
match for the observed behavior of these dwarf galaxies. According to Mariana
J£lio, a PhD student at the AIP and the lead author of the study:
The study challenges the RAR paradigm by providing better and more in-depth
analysis, allowing astronomers to properly infer the radially resolved profiles
of dwarf galaxies. They further confirm what astronomers suspected about dwarf
galaxies and how they do not conform to the expectations of their more massive
counterparts. Said co-author Professor Justin Read from the University of
Surrey:
While the findings do not address the outlying questions about DM (e.g., what
it's composed of) or confirm its existence, they do narrow the search by
helping to rule out alternative explanations. Future observations that target
even fainter and more distant galaxies will further narrow the search, and
scientists will do so with confidence that DM is still the most likely
explanation for what we see out there.
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