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Questions tagged [galaxy-clusters]

This tag is for questions relating to the galaxy cluster or the cluster of galaxies, gravitationally bound grouping of galaxies, numbering from the hundreds to the tens of thousands. The important fact about it is that , collisions between galaxy clusters provide a unique opportunity to study matter in a parameter space which cannot be explored in our laboratories on Earth.

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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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2 votes
3 answers
1k views

Why isn't the "Dark Matter" in the Bullet Cluster supermassive black holes?

I've seen several videos that claim that the Bullet Cluster is evidence for Dark Matter. The general idea is that the gas is trapped on one side of the collision and the light-bending "Dark ...
The Shepard's user avatar
2 votes
2 answers
181 views

How does dark energy affect the dynamics of galaxy clusters?

Galaxies interact with each other gravitationally (just as every other celestial object) and in many cases they form groups or clusters. Does the expansion of the universe (or dark energy) affect the ...
vengaq's user avatar
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0 votes
0 answers
40 views

Pressure and velocity dispersion

I’m reading this paper whose Eq(2) I’m a little concerned about. Sanders has tried to relate the pressure with the velocity dispersion of particles using the relation $P= \rho\sigma^2$ where $\sigma$ ...
Ambica Govind's user avatar
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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0 votes
1 answer
185 views

How did Zwicky discover dark matter?

According to Wikipedia Zwicky used "virial theorem" to discover the gravitational anomaly in the Coma Galaxy cluster. But I also remember reading that he used Kepler's third law. Which one ...
zeynel's user avatar
  • 217
2 votes
0 answers
35 views

Dwarf galaxy rotation speed around Andromeda/Mily way

We know that the rotation speed of stars around the center of a galaxy is roughly flat. But how fast does the dwarf galaxy rotate around the bigger galaxy, say andromeda or milky way? Do they also ...
Angela's user avatar
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1 vote
0 answers
56 views

Database for galaxy luminosity (or mass) distribution

I'm trying to get data on luminosity (or mass) distribution for galaxies. I came across one paper (https://arxiv.org/abs/1106.3564) which gives luminosity distribution for Andromeda. But is there any ...
Angela's user avatar
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1 vote
1 answer
93 views

Distance $r$ between galaxies inside the galaxy cluster

I am currently working on the dynamics of the galaxy cluster, so i am trying to get the distance $r$ between the galaxies inside the galaxy cluster from its centre. As a input i have RA , DEC and Z ...
Atul's user avatar
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3 votes
1 answer
53 views

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
4 votes
0 answers
75 views

How loud is the Perseus cluster?

The gas near the center of the Perseus cluster exhibits quasiperiodic pressure oscillations that can be interpreted as sound. I found a paper that says that these pressure waves have a wavelength of ...
tparker's user avatar
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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
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0 answers
33 views

Does a star that is far from any galaxy tend to rotate slower?

I'm wondering whether the rotation of a galaxy and the buffeting of the gas and dust within it by light and stellar wind and pressure waves makes nebulae or gas clouds in galaxies have more angular ...
Matthew Christopher Bartsh's user avatar
1 vote
0 answers
68 views

Why is the Hubble law so accurate at scales smaller than galactic voids?

It's possible to derive the Hubble law: $$v = H_0 d$$ from the FRW metric by differentiation. Experimentally the Hubble law appears to hold for relatively small distances, say 20 Mpc and smaller. ...
Kris's user avatar
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1 vote
2 answers
202 views

Are galaxies and clusters of galaxies much denser when we observe the 'past' far universe than the 'present' closer part of the universe?

Are galaxies and clusters of galaxies much denser when we observe the 'past' far universe?If the universe is expanding, the galaxies should have been much closer in the past so should we see a larger ...
Janko Bradvica'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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0 answers
69 views

Do all gravitationally collapsing objects virialize?

For interactions via a Newtonian gravitational potential, the virial theorem states that $$ 2 \langle T \rangle = -\langle V \rangle $$ i.e. the time-averaged total kinetic energy and total potential ...
Socob's user avatar
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1 answer
384 views

What causes peculiar velocities of galaxies?

The Wikipedia page on the subject states: Galaxies are not distributed evenly throughout observable space, but are typically found in groups or clusters, where they have a significant gravitational ...
Hiroyashu's user avatar
  • 280
2 votes
1 answer
62 views

What will be the eventual result of the Milky Ways future mergers?

I am wondering, after the Milky Way merges with Andromeda and other near by dwarf galaxies and globular clusters, will it then merge with galaxies in the Virgo cluster and even Laniakea? And if so ...
RandySavage's user avatar
3 votes
1 answer
541 views

Star distribution (density of stars) as a function of distance from Galaxy centre?

Is there any mathematical formula or empirical relation that defines the density of stars as a function of distance from the Galaxy centre in a spiral galaxy?
user210956's user avatar
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2 votes
1 answer
214 views

Formula for the bias of galaxies

From the article "Large-Scale Galaxy Bias", I try to deduce the equation that my teacher told me which links 2 quantities: the global number density of galaxies the local number density of galaxies ...
user avatar
0 votes
1 answer
69 views

Why are galalxies spiral? [duplicate]

In every picture we see that galaxies are spiral, why so? are there any other shapes possible?
Turing101's user avatar
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0 votes
1 answer
285 views

Temperatures of Galaxy Clusters

Recently I've read about clusters of galaxies and have tried to understand how one can measure their mass and temperatures. Clearly, we can physically measure a couple of things such as the flux of X-...
LightningStrike's user avatar
1 vote
1 answer
83 views

Doubts about the formation of the bullet cluster

The bullet cluster is formed by the collision of two clusters of galaxies. After the collision, the stars and galaxies in those two clusters passed through each other. But the intergalactic gas clouds ...
Solidification's user avatar
1 vote
2 answers
427 views

Are there super-super black holes in the center of super clusters?

If a galaxy contains a super-massive-black hole at it's center. Is there anything likely to be at the center of a super-cluster of galaxies? Or to put it another way, are there likely to be any ...
user avatar
1 vote
2 answers
306 views

What is the biggest structure in the Universe?

The CMB cold spot (if it exists) may imply a supervoid of approximately 1 billion light years across. If the diameter of the Observable Universe is 46 billion light years this is about 2% the ...
user avatar
2 votes
0 answers
161 views

Total number density of galaxies and problematic expression in practise

I am asked to give the formal expression of the total number density of galaxies and explain why is this expression problematic in practice. From what I saw from my research and into my lectures, I ...
user avatar
1 vote
1 answer
282 views

Is it likely that galaxy supercluster attractors are all supermassive blackholes?

Really any phenomena about matter pulling into something always results to one thing eventually with enough mass, a black hole. I understand that the Shapely attractor is oftentimes referred to as the ...
Neuromeda's user avatar
  • 147
1 vote
1 answer
116 views

Do attraction between two galaxies count for dark matter?

We know that the uniform rotation curve of individual spiral galaxies does require presence of some form of dark entity (matter). Does the attraction between two (or more) spiral galaxies also require ...
kpv's user avatar
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0 votes
1 answer
79 views

Orbits within orbits

Do galaxy clusters have structured orbits (e.g. ellipticals)? If not, why not? Moons orbit planets, planets orbit stars, and stars orbit galactic centres. Is there something different about the ...
Tom B's user avatar
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1 vote
0 answers
78 views

If dark energy disappeared today, what would be the largest gravitationally bound structures in the universe?

In particular, what would be the largest gravitationally bound structure containing the milky way? As a bonus, how does this compare to the largest gravitationally bound structures assuming a ...
Stephane Bersier's user avatar
0 votes
1 answer
329 views

How many filaments are there in the observable universe? [closed]

How many filaments are there in the observable universe? I couldn't find any list on Wikipedia.
Alper's user avatar
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1 vote
0 answers
30 views

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 ...
foolishmuse's user avatar
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0 votes
1 answer
160 views

Can't we obtain observational values for scale factor at different periods in the history of the universe?

This may be a stupid question, but it seems to me that we could calculate the value of the scale factor at any stage in the history of the universe by analysing the relationship between recessional ...
Max's user avatar
  • 485
2 votes
2 answers
2k views

Is there an average distance between groups of galaxies such as our Local Group?

I believe our Local Group is $10$ million light years in diameter and, depending on which article I read, has $30-52$ galaxies. But what about other galaxy groups? How far would they be? I ...
user avatar
2 votes
1 answer
510 views

Why elliptical galaxies congregated toward the cluster center?

When we look at a rich galaxy cluster, why is it that elliptical galaxies tend to live near the center while spiral galaxies tend to live at the outskirt?
WeiShan Ng's user avatar
5 votes
1 answer
1k views

Do dark flow findings suggest we're moving towards distant gravitational anomaly?

The (somewhat) recent paper "Probing the Dark Flow signal in WMAP 9 yr and PLANCK cosmic microwave background maps" (submitted in 2014) by a team lead by the researchers at NASA's Goddard Space Flight ...
Jason R. Mick's user avatar
0 votes
1 answer
463 views

Gravitational potential energy in terms of half-mass radius

In Barbara Ryden's Intro to Cosmology, she states that the gravitational potential energy of a cluster of galaxies, that is given by $$ W = -\frac{G}{2}\sum\limits_{i,j,\ i\neq j}\frac{m_im_j}{|\vec{x}...
JonTrav1's user avatar
  • 970
1 vote
1 answer
681 views

Calculating velocity in particular reference frame given redshift

I am trying to do some analysis of galaxy velocities within cluster environments. This involves finding the velocity of that galaxy with respect to the cluster-frame, or the "proper velocity", $v_i$. ...
user avatar
2 votes
0 answers
31 views

What is the plot function: number of galaxy-clusters ( gravitationally bound objects) within the cosmic event horizon vs. time?

I found this nice animation about the shrinking cosmic event horizon:http://yukterez.ist.org/lcdm/i.html#comoving But now I am interested about the number of galaxy clusters (biggest gravitationally ...
Randy Welt's user avatar
3 votes
4 answers
170 views

Structure formation: Galaxies as different entities and stars as groups

Why do stars exist in groups like galaxies rather than individual stars, and why do galaxies exist as different entities without continuity and with large intergalactic spaces?
Enock Kabibi's user avatar
48 votes
3 answers
8k views

Why don't galaxies orbit each other?

Planets orbit around stars, satellites orbit around planets, even stars orbit each other. So the question is: Why don't galaxies orbit each other in general, as it's rarely observed? Is it considered ...
user avatar
2 votes
1 answer
206 views

Ideal Gas Law in a Rotating Galaxy Cluster

There is evidence that some galaxy clusters may experience some bulk rotation. If this is true, how valid is it to use the Ideal Gas Law to estimate the mass (actually, it calculates the acceleration ...
user avatar
1 vote
3 answers
1k views

The formula for the hydrostatic equilibrium of a rotating mass of gas

This is a follow up question to Hydrostatic Equilibrium in a Galaxy Cluster. Is this a reasonable estimate of the hydrostatic equilibrium equation for a spinning mass of gas? $$\frac{v(r)^2}{r} - \...
user avatar
1 vote
1 answer
884 views

Hydrostatic Equilibrium in Galaxy Clusters

One of the methods of mass calculation in Galaxy Clusters is to make a profile of the X-Ray gas and then (after several assumptions) assume hydrostatic equilibrium: the force pushing down on the gas (...
user avatar
1 vote
3 answers
404 views

Why does the gas in the Bullet Cluster act like a lens?

In the Bullet Cluster, we have two well defined galaxy clusters that exhibit gravity lensing. Between them is a mass of gas (mostly hydrogen and helium) that is roughly eight to nine times the mass ...
user avatar
0 votes
1 answer
1k views

Gas Mass Calculation in Galaxy Cluster

Rob Jeffries found this document for me that describes how the X-Ray emissions from galaxy clusters are used to calculate the mass of the cluster. I'm unable to follow the steps to calculating the gas ...
user avatar
0 votes
1 answer
243 views

Coma Cluster X-Ray Mass

Does anyone have a reliable reference for the x-ray mass of the Coma Cluster? I've got a value of $3\times10^{13}\: M_⊙$ from Gursky's 1971 report. Anything more recent would be appreciated.
2 votes
1 answer
545 views

Understanding X-Ray emitting gas calculations in Galaxy Clusters

This is a follow up to a question I asked about the Bullet (and Coma) cluster. I've read several papers now about the fact that galaxy clusters collect overdense areas of hydrogen which emits X-ray ...
user avatar
4 votes
4 answers
2k views

Bullet Cluster and MOND

Apparently the Bullet Cluster is some slam-dunk proof of ΛCDM. The argument seems to be that most (>90%) of the baryonic mass in these clusters is in the form of X-ray emitting gas. Therefore the ...
user avatar