- 4051 - DARK
MATTER - what simulations tell us? Dark Energy is the mysterious force that is
expanding the Universe causing all matter not held by gravity to accelerate
apart. Dark matter is the invisible
material that makes up the vast majority of the universe's mass, it may collect
itself to form atoms.
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------------------ 4051 - DARK MATTER - what simulations tell us?
- Those "dark
matter atoms" might radically alter the evolution of galaxies and the
formation of stars, giving astronomers a new opportunity to understand this
mysterious substance.
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- Dark matter makes
up over 80% of the mass of every galaxy and cluster of galaxies in the
universe. All of our observations suggest that dark matter is some new kind of
particle, one that does not interact with normal matter or even with light. We
can identify dark matter only through its gravitational interactions with
everything else. Whatever dark matter is, it is beyond our current understanding
of physics. But it still has mass, so it still has gravity.
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- We do not yet know
if dark matter is simple or complex. It may be made of only one kind of
particle that dominates the universe and barely interacts with even itself. Or
it may be made of multiple types of particles, with as rich a variety as we see
in normal matter.
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- We know of only
four fundamental forces of nature: gravity, electromagnetism, the strong
nuclear force and the weak nuclear force. But there may be additional forces
that operate only among the dark matter particles and do not interfere with
normal matter at all.
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- The concept of
additional dark matter particles and dark forces isn't as far-fetched as it may
seem. Our understanding of physics is built on symmetries, which are deep
mathematical relationships between particles. It could very well be that there
are additional symmetries in the laws of nature that make dark matter a twin of
normal matter and that, for every kind of interaction that normal matter can participate
in, there is a counterpart in the dark sector.
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- For example, with
normal matter, we can build simple atoms: a proton and an electron bound
together, with the photon, the carrier of the electromagnetic force, mediating
the interaction. We could also have a dark matter version of that same
structure, with a dark proton bound to dark electrons via dark photons: dark
atoms.
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- Atomic dark matter
would behave much differently than dark matter composed of only a single
particle. Most importantly, simple dark matter would have a very difficult time
clumping up, only doing so slowly over hundreds of millions of years.
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- Normal matter
collects in those smooth pools of dark matter to form galaxies, but otherwise,
the two lead separate lives. Atomic dark matter, however, could form its own
shadowy galaxies, disk-like structures that mimic the size and layout of
visible galaxies.
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- Astrophysicists
used this intriguing possibility to simulate the evolution of galaxies and see
what observable differences might arise. They allowed the atomic dark matter to
evolve according to its own forces and then examined how those new structures
would affect visible galaxies through the new arrangement of gravity.
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- The researchers
found that even a small amount of atomic dark matter, as little as 6% of all
the dark matter in the universe, leaving the rest to be simple, was enough to
radically alter the evolution of galaxies. Because the atomic dark matter could
interact, it could easily clump together by losing energy through the emission
of some form of dark radiation. The simulations revealed that a "dark
disk" quickly appeared within each galaxy, with the spin of the disk
closely matching that of the visible, normal components.
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- From there, the
atomic dark matter continued to clump, just like normal gas clumps into clouds
and, eventually, stars. In the simulation, the atomic dark matter formed dark
stars of its own and could even trigger the formation of its own black holes.
Those clumps then sank into the core of the galaxy, where the density
increased.
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- With all that
extra gravity, star formation in the cores of galaxies kicked into overdrive,
producing stars at a much faster rate than in galaxies with simple dark matter.
These simulations actually ruled out some models of atomic dark matter, because
those models caused their galaxies to run out of new material for making stars
far too quickly.
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- But some models
survived current observational limits, allowing for the continued possibility
of atomic dark matter. The researchers hope that further theoretical and
experimental studies will shed light on the plausibility of this intriguing
form of exotic matter. Because atomic dark matter clumps so efficiently, we
might be able to spot dense, star-like clumps with upcoming gravitational
microlensing studies.
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June 12, 2023 DARK MATTER
- what simulations tell us? 4051
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Tuesday, June 13, 2023 ---------------------------------
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