Questions tagged [galaxy-clusters]

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1answer
16 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?
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1answer
176 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 ...
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1answer
56 views

Why are galalxies spiral? [duplicate]

In every picture we see that galaxies are spiral, why so? are there any other shapes possible?
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1answer
50 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-...
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1answer
64 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 ...
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2answers
104 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 ...
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2answers
123 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 ...
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0answers
111 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 ...
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1answer
55 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 ...
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1answer
71 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 ...
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1answer
68 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 ...
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59 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 ...
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75 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.
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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 ...
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1answer
104 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 ...
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1answer
82 views

Original distance from us to galaxy at redshift of z=6 if we know the current distance and taking into account universe expansion?

So I'm given that a galaxy cluster is currently at redshift z = 6 and the question asks "what was its distance from us at the time the light left the cluster?" We only know the redshift, but the ...
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2answers
665 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 ...
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1answer
191 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?
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931 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 ...
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1answer
307 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}...
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1answer
281 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", $v_i$. ...
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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 ...
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4answers
145 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?
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3answers
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 ...
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1answer
140 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 ...
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3answers
636 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} - \...
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1answer
586 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 (...
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3answers
296 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 ...
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410 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 ...
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1answer
190 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.
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1answer
294 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 ...
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4answers
974 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 ...
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2answers
171 views

Do galaxy clusters follow De Vaucouleurs' law?

Do galaxy clusters follow De Vaucouleurs' law? If objects in the universe are built hierarchically, wouldn't one expect a galaxy cluster that is roughly spherical to follow the same profile as an ...
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1answer
75 views

Mass to Light Ratios

I know that the mass to light ratio for galaxies is between 2 and 10. I also know that the ratio changes primarily based on what kind of galaxy you have (elliptical, spiral, etc). Is there a table ...
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2answers
162 views

Why do so many galaxies in clusters have a near zero velocity?

I'm looking at a velocity chart of the Coma Cluster: And the question occurred to me: why are there so many galaxies that have a zero velocity (relative to the core of the Coma Cluster which is ...
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131 views

Galaxy Cluster Data

I have a modification to ${\rm MOND}$ that appears to work much better than 'Standard' ${\rm MOND}$ at the galactic scale. I want to test this model now on larger structures. Does anyone know where ...
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0answers
224 views

Gravitational lensing on galaxy cluster with given potential

I am having a problem with gravitational lensing question where we are interested in deflection angle of light traveling in potential of galactic cluster, described with tensor $h_{00}=\frac{a}{\sqrt{...
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8answers
5k views

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero?

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero? I just do not see why our model must work the way ...
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1answer
551 views

Correlation between large-scale galaxy structure and CMB fluctuations?

During a relatively non-technical astronomy seminar the other day, the speaker displayed the famous WMAP full-sky image as an aid to describing what the CMB is, the scale of its fluctuations, etc. ...
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126 views

What causes there to be an offset between the light lensing through the space neighboring galaxy clusters and the galaxy clusters themselves?

http://www.wired.com/wiredscience/2013/01/musket-ball-dark-force/ The reason this is strange is that dark matter is thought to barely interact with itself. The dark matter should just coast through ...
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108 views

When spacetime expands to the point where galaxy clusters are not observable, will there by any interaction?

It's my understanding that in a few billion years, clusters of galaxies won't be able to directly observe one another due to the expansion of spacetime overcoming gravity between those clusters. ...
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483 views

Redshift and shapes of galaxy clusters

How does peculiar velocities lead to the observed elongation of galaxy clusters in redshift space, otherwise known as the Fingers of God effect? I have read the relevant Wikipedia page, but cannot ...
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833 views

Does conformal gravity explain the Bullet cluster lensing effects?

Conformal gravity is an "alternative" theory of gravity, where instead of using the Einstein-Hilbert action composed of the Ricci scalar, the square of the conformal Weyl tensor is used. It was ...