Questions tagged [structure-formation]

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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., ...
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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 ...
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Why the density perturbation of Newtonian and Comoving gauge are the same in the sub-horizon limit?

In Daniel Baumann's Cosmology lecture note for UvA Masters Course Cosmology: http://cosmology.amsterdam/education/cosmology/, when discussing the cosmic perturbation theory of matter, the author ...
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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 ...
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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, ...
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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 ...
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Large Scale Structure: Math proof that power spectrum being zero at a scale means fluctuations have variance of underlying Gaussian field

(Please don't close this one as a homework question. I am self taught and I have no way to get this information from any other source besides asking it here.) I am trying to solve this question (11.6) ...
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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 ...
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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 ...
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Matter power spectrum in cosmology

In cosmological simulations, we take the matter power spectrum as $P(k)=k^n$ (eg. Harrison-Zeldovich spectrum). What is the motivation behind this? Can we arrive at this from a more general theory?
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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 ...
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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 ...
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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 ...
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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)?...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 -> ...
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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. ...
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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-...
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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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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Deriving the continuity equation for a perturbation from the continuity equation for the full density

I am attempting to derive the continuity equation for a density perturbation $\delta$, given the continuity equation for the full density $\rho(\mathbb{x}, t)$. This is in the context of cosmological ...
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Horizon entry, Meszaros suppression and start of perturbation growth

I thought that the onset of perturbation growth was determined by horizon entry of the perturbation (because there won't be a gravitational collapse of an over dense region not causally connected to ...
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Which decoupled first? The dark matter or the CMB photons?

According theories that work best for the structure formation which happened first in the history of the evolution of the Universe, the decoupling of dark matter or the decoupling of photons? How sure ...
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Decreasing water pressure toward top of tank walls

A contractor who is building a freestanding water storage tank of 6m (length) x 2m (width) x 1.5m (depth) suggests stepping out halfway up the walls (fibreglass sat in an iron frame) by 2cm to ...
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What is/causes this 3D dust structure?

I was recently on a flight and noticed some strange objects located inside the plane window. To me, it looks like dust which has arranged itself into a complex hydrocarbon-like structure, with ...
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Has the gaseous cosmic web ever been directly observed?

For a couple of decades now we've had maps of the cosmic web as traced by galaxy positions from redshift surveys like the 2dfgrs: Are there any similar maps which rely on gaseous tracers? I guess ...
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What causes structure formation: Baryon acoustic oscillations or inflation?

Formation of structures such as galaxies and galaxy clusters require anisotropies in the cosmic plasma which (as I understand) were due to the anisotropies or density inhomogeneities created by Baryon ...
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Why do the sun and planets differ in their chemical elements composition?

The chemical elements composition of the sun changes as its nuclear furnace changes elements into heavier ones. But it is supposed to be mostly Hydrogen at the start. The planets are too cold for ...
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How are sand blocks formed?

My son asked me at the beach how are "sand stones" formed. These are the solid (but fragile) sand conglomerates which you can hold in your hand and which crumble to sand once pressed. I tried some ...
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Are galaxies merely groups of nearby stars that collected together, or do the stars share a common birth? [duplicate]

The news that some galaxies have dark matter and others do not leads to the question of how this could be possible. If galaxies are merely groups of stars that gathered together (under gravitational ...
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Gödel's Solution as background for a star patch

In Gödel's "Example of a New Type of Cosmological Solutions of Einstein's equation of Gravitation", all prior cosmological solutions with a non vanishing energy density have a property of all world ...
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Is there evidence the great attractor isn't just gravitationally lensed gravity?

Is there any evidence that the great attractor isn't just gravitationally lensed gravity? It seems odd that it would be directly on the other side of the black hole at the center of our galaxy and ...
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Why are all galaxies roughly the same size?

what determines the stable mass of galaxies, stars, star clusters or even galaxy clusters? Is there some obvious way to determine the classes of stable mass clusters from the initial conditions of the ...
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Can collapsing of the first star cause a staggering chain reaction throughout the universe?

Forgive me but I am not an academic but I have an enormous curiosity and am more or less teaching myself. I stumbled upon this site totally by accident and have relished the information here - ...
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Shell crossing in voids in spherical collapse model

What would be a necessary and sufficient for shell crossing to occur in an underdense region evolving based on spherical collapse model? i.e; shells moving outward with differential acceleration?
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If all the Structure in our visible Universe originated from Quantum Fluctuations, why isn't there as much Anti-Matter as Matter?

According to inflation, all the structure that we see like galaxies, etc. originated from quantum fluctuations which were expanded during inflation. But since quantum fluctuations always create ...
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