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Questions tagged [structure-formation]

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How to call ellipse packing structures?

My research group and I are trying to figure out what is the correct terminology for two different packing structures of 2D ellipses. The two structures are displayed below as Structure A and ...
JamesKUtterback's user avatar
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Scale dependent density growth in sub-horizon scales

In standard cosmology, we use \begin{equation} \ddot{\delta} + 2 H \dot{\delta} - 4 \pi G_N \rho \delta=0 \tag{1} \end{equation} to study the structure growth in sub-horizon scales. However, at the ...
t-rex's user avatar
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Density perturbation equation

I have seen people deriving: $$\ddot{\delta} + 2 H \dot{\delta} - 4 \pi G \rho \delta=0 \ ,$$ from combining Continuity, Poisson and Euler equations. I wanted to derive it from the perturbed $00$ and ...
t-rex's user avatar
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1 vote
2 answers
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Interplay between gravity and cosmic expansion causing collapse of large-scale structures?

As far as I understand it, in the context of large structure formation, the interplay between gravity and cosmic expansion can cause certain anisotropies in voids that can make them collapse (https://...
vengaq's user avatar
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Voids blueshifting CMB photons (in certain cases)?

I have some questions about this interesting work (https://iopscience.iop.org/article/10.1086/517603/pdf) where the authors analysed the effects of voids in the CMB radiation (particularly through the ...
vengaq's user avatar
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Questions about cosmic sheets/walls/filaments

I had a couple of questions about cosmic filaments in the context of the cosmic web structure formation: In this thesis (https://www.imprs-hd.mpg.de/51939/thesis\_cpenzo.pdf), the author indicates in ...
vengaq's user avatar
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Cosmic web distribution and neuron system similarities

Does the cosmic web follow Gaussian distribution? If so, is that the reason it resembles the human neuron system? Does the human neuron system follow Gaussian distribution too? (sorry if this deviates ...
Kellan Heerdegen's user avatar
1 vote
1 answer
79 views

Cosmic web shape

Does anybody know why the cosmic web is shaped like a web? I feel like it would be more likely that it is more like a galaxy with a supermassive black hole in the center, if that were true, what would ...
Kellan Heerdegen's user avatar
1 vote
1 answer
125 views

What if gravitation was the only force? [closed]

This is a follow up of Interactions within constituents of dark matter . I wonder about dark matter, and, naturally, compare it with our observable world. If gravitation would be the only force acting ...
Gyro Gearloose's user avatar
1 vote
3 answers
144 views

Why doesn't frozen-out dark matter annihilate later during structure formation?

The so-called freeze-out of dark matter is based on a homogeneous description. However, in the later stages of the universe, where structures form, it seems very likely that the reaction rate would ...
Bababeluma's user avatar
1 vote
1 answer
72 views

Cosmological constant, dynamical friction and structure formation?

I would like to ask a question about an interesting article that I found (https://repositorio.unesp.br/server/api/core/bitstreams/b8a5a5b8-4b3b-4198-9f5d-bf69431db1ae/content) In the context of ...
vengaq's user avatar
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How to intuitively understand the Boltzmann equations that come up in Cosmology?

This may be a silly question, but I have been reading through Dodelson's Modern Cosmology textbook and n Chapter 4 we derive the Boltzmann equation for different constituents of matter and radiation. ...
user3461947's user avatar
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1 answer
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Size and boundary of the Milky Way Galactic disk

I have been pondering a question that arose while I was reading a research paper that mentions galactic disk stars have been found up to distances as far as 25 kpc from the galactic center and ...
HDhaliwal's user avatar
1 vote
0 answers
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The 'core-cusp' problem for dark matter halos in larger galaxies

TLDR: Do observations of larger galaxies favour 'cuspy' dark matter halo distributions, as predicted by N-body simulations? I've been trying to understand the 'core-cusp' problem for dark matter halos ...
H-QM-W's user avatar
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Is the $σ8$ tension in the ΛCDM cosmology evidence that the amount of Dark Matter (DM) in the universe is increasing?

Strong evidence is provided by recent cosmological studies that “clumpiness” in the large scale structure (LSS), as measured by $σ8$, is decreasing (for example, “Hyper Suprime-Cam Year 3 Results…”, X....
RalphW's user avatar
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3 votes
2 answers
157 views

Is there dark matter in intergalactic space?

Reference: the rotation speed of galaxies in a galaxy cluster: Is the dark matter associated with each galaxy in a cluster, sufficient to explain the rotation speed of galaxies in the cluster, or ...
Angela's user avatar
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4 votes
1 answer
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Why does non-baryonic matter give structure formation a head start?

This image is from the textbook by Ryden. It shows that the density perturbation was able to grow earlier if there were non-baryonic dark matter, why is that?
ABC's user avatar
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1 answer
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If spiral galaxies form due to perturbations, why aren't there more spiral galaxies in galaxy clusters, where interaction/perturbation is likely?

I read the other article with an excellent explanation of simulation results and the mathematics behind spiral arm formation yet was left baffled by the point that the principal influence that would ...
Thom Revay's user avatar
3 votes
1 answer
56 views

What are the consequences of the tidal friction on the galaxy?

In the Earth-Moon system tidal-friction slows down the rotation, so does it do the same for the galaxy? If not how come, and why it's different than on Earth? If so can this slow-down be the reason ...
zebra's user avatar
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What process led to the era of Reionization in the early Universe?

Reionization was the second major phase transition in the early Universe. At the wiki article for the epoch of Reionization in the early Universe, it states: The second phase change [i.e., ...
Daddy Kropotkin's user avatar
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1 answer
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Why are most ring galaxies present in the field instead of rich galaxy clusters?

I was reading an article in which it said that mostly ring galaxies are present in the ‘field’ instead of rich galaxy clusters. Can anyone explain why is it so? I read about it's formation and i ...
25 Simran Tiwari's user avatar
1 vote
1 answer
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Understanding primordial Statistical Fluctuations in the Universe

I am trying to answer the question, Whether gravitational collapse began from Statistical fluctuations in the early Universe? In order to answer this I must find out the total number of particles in ...
CTZenScientist's user avatar
4 votes
2 answers
116 views

Does magnetism play a role in the formation of galaxies?

Forgive my ignorance as I know next to nothing about physics. From my layperson's understanding, galaxies are formed primarily by the interaction of gravitational forces of stars and planets, however, ...
user148298's user avatar
9 votes
1 answer
1k views

Could the center of the galaxy explode as a result of a chain reaction of stars going supernova?

I was reading "Ringworld" by Larry Niven. I'll spare you most of the details of the story, and say that one of the parts of the plot is that the center of the Milky Galaxy blows up, because ...
Curious Layman's user avatar
3 votes
0 answers
76 views

Is there an intuitive reason we might expect the physical universe to be based on the types of structures seen in quantum field theory? [closed]

With the exception of gravity, the physical universe behaves so far as we know, in line with mathematical structures such as groups, fields, and specifically invariant fields. Of course nobody knows ...
Stilez's user avatar
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How do bars in barred spiral galaxies form?

There is this same question in astronomy stackexchange. But its only answer is unfortunately a rather unsatisfying quote which I could not even find within the provided link. Also, that question is ...
Luismi98's user avatar
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1 vote
1 answer
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Entropy and large-scale structure of the universe

In their article Disturbing Implications of a Cosmological Constant, Leonard Susskind and others write: Certainly, given enough time and a suitable inflaton, recurrences will eventually bring the box ...
Арман Гаспарян's user avatar
2 votes
0 answers
70 views

Does barred in spirals galaxies like ours have the same speed (spin) as the center black hole?

In the case of old galaxies (elliptical) the black hole, like one in M87 have 2 jets. This look like polarisation pushing from central BH. In barred spiral galaxies, the bar have to cross the central ...
Jean-Louis Boucher's user avatar
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Types of black hole formation

NASA says: Stellar black holes form when the center of a very massive star collapses in upon itself. There, stars usually grow and collapse by the accretion of gas. This paper ("Formation of ...
2080's user avatar
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1 answer
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Do temperature and pressure affect alumina properties?

Alumina is a ceramic, an electrical insulator, but has a relatively high thermal conductivity with a high melting point. So can all those properties change under pressure and temperature (low or high)?...
autodidact's user avatar
2 votes
0 answers
36 views

Galaxy statistics calculation in Saslaw's book

I am trying to follow a calculation from the book of William C. Saslaw, The Distribution of the Galaxies: Gravitational Clustering in Cosmology. The calculation is shown on the pages following page ...
Shaz's user avatar
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2 votes
1 answer
300 views

Catenary shape of transmission lines

When flexible metal transmission lines are hung between two poles, the shape they assume to minimize the action of gravitational and tensile forces is a called a catenary. While assuming that shape, ...
kbakshi314's user avatar
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0 votes
1 answer
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Vertex deviation of the velocity ellipsoid

Context I will be working here in galactic coordinates. This system uses distance from the Sun $(r)$, longitude $(l)$ and latitude $(b)$. The latter two are angles defined as shown in the following ...
Luismi98's user avatar
  • 401
1 vote
1 answer
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Galaxy Superclusters

Okay quick question... why is it that when galaxies group together in superclusters they form a sort of branch-like shape? I personally would think they’d all just group together in some sphere or ...
PythonerLMAO's user avatar
0 votes
4 answers
81 views

Homogenous Universe (Earthlike planets?)

The fact that the Universe is homogenous can lead to a conclusion that there are another earthlike planets, or planets like earth are considered as some differences that are allowed in the definition ...
Konstantina-Dimitra P.'s user avatar
3 votes
1 answer
129 views

Did the dominant cosmic structure forming force change over time?

Hypothesis During an earlier epoch the universe was filled with hot dense plasma. During this time the dominant structure forming force was electromagnetic. As plasma is prone to self organizing the ...
christo183's user avatar
1 vote
0 answers
22 views

How does the ionic radius influence the ion's interaction?

What can we deduce about an ion, its interaction or the structure it is in, based on the ionic radius? My understanding of the concept of the ionic radius is that these are seen almost as having a ...
user7077252's user avatar
6 votes
2 answers
458 views

Andromeda & Milky Way Merger: Gravitational Waves

When the Andromeda galaxy and Milky Way merge in the future, the super-massive black holes at their respective galactic centers will likely eventually merge. Similarly to the gravitational waves ...
Jan Stuller's user avatar
2 votes
0 answers
55 views

Does the rate of change of entropy vary in time

John wheeler once jokingly said he was feeling uneasy putting a hot cup next to a cold cup as he'd be contributing to the entropy of the universe or at least accelerating it. Then again the very ...
Kugutsu-o's user avatar
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Theories of galaxy structure

If you look up galaxies on Wikipedia (at least as of August 14, 2020) you will find a list of classes of galaxies that progresses roughly as follows: Elliptical galaxies Shell galaxies Spiral ...
TLDR's user avatar
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0 votes
1 answer
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3 x 2 or 6 x 2 Surface Reconstruction

I encountered expressions such as "3 x 2 surface reconstruction" or "6 x 2 surface reconstruction" while studying. I understand surface reconstruction refers to the movement of ...
JustStartedStudying's user avatar
2 votes
0 answers
47 views

Possible structures in 1D [closed]

Suppose we have 1D crystal of several types of atoms. How many fundamentally different structures exist? The obvious are the grid and the random distribution. Substitution system A -> ABA, B -> ...
lesobrod's user avatar
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3 votes
1 answer
271 views

What is the need for smoothing the cosmological density field?

I have recently started reading about the Press-Schechter formalism in cosmological structure formation, but what I still do not understand is why we need a smoothed density field in the first place. ...
Suyama87's user avatar
0 votes
1 answer
113 views

Does cosmology assumes that matter existed before the Big Bang?

In cosmology, studying the evolution of the matter perturbations for structure formation, one frequently mentions "horizon entry", meaning that a perturbation of (fixed) wavelength is super-...
Mauro Giliberti's user avatar
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4 answers
1k views

Why don’t almost all solid bodies merge into one body when they come in contact?

Macroscopic bodies in solid state when they touch each other do not connect in one monolithic body, because of electrostatic repulsion of their electron clouds. Okay. Say, have two iron ingot, we ...
Artur's user avatar
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3 votes
2 answers
141 views

When the star formation begins?

We can separate the history of the universe in different epochs. Radiation dominated epoch, matter dominated epoch, and dark energy dominated epoch, and we can divide the epochs in different ways. ...
Nothing's user avatar
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1 vote
0 answers
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Required Preconditions for Galactic Formation

In recent weeks, I have been working on building simulations to look at the formation of galaxies from dust clouds. It's a relatively crude simulation at this point as I needed a working model to ...
BooleanDesigns's user avatar
-2 votes
1 answer
66 views

Multiple levels of expansion of space? [closed]

It can easily be seen from the plot that there are at least 3 gaps between objects in the large, there is the gap between the planets and the moons, and between the planets and stars, and between ...
OzOz's user avatar
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0 votes
1 answer
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Do post-big-bang quantum fluctuations determine star and planet formation?

It is my understanding that cosmology simulations largely implement general-relativity, taking quantum-effects into account merely by setting the fluctuations in the initial conditions. In the real ...
PhysicsTeacher's user avatar
1 vote
1 answer
1k views

Steinhardt order parameter and radial distribution function

Is there a relation between the probability distribution of Steinhardt order parameter for BCC and FCC and their radial distribution function? In the picture we see the probability distributions of ...
Suslik's user avatar
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