# galaxies's questions - English 1answer

391 galaxies questions.

### 3 How are velocity and dispersion maps of galaxies made?

How can I get the velocity dispersion and velocity maps of galaxies given 3D data cubes obtained using an integral field spectrograph?

### 3 Galaxy Rotation Speeds and General Relativity

Is it true that the predictions from the General Theory of Relativity don’t match the observations of galaxy rotation speeds, and that this then started the search for dark matter? Is it only the ...

### 5 Population I and II stars

I have been thinking about the formation of the galaxy. I can easily understand that old, low-metallicity stars are in the halo, but I'm missing something when it comes to the disk. If slowly-...

### 4 Why are jets not commonly found in spiral galaxies?

1 answers, 85 views astrophysics galaxies
Jets and radio lobes are generally associated with elliptical galaxies. Why not spirals?

### Are cosmological distances additive?

1 answers, 196 views cosmology galaxies distance
If we observe two galaxies that are diametrically opposed from the Earth, and each $1000\,{\rm ly}$ away from the Earth, is the separation distance between the galaxies $2000\,{\rm ly}$? Really the ...

### 5 How much gas is in elliptical galaxies?

1 answers, 448 views galaxies
It is widely known that elliptical galaxies have relatively little or no measurable gas, but how is this determined? What is the amount of gas? Is there a known ratio of stellar mass to gas for ...

### Could the rotation of far away galaxies appear faster than they really are? [duplicate]

The necessity of dark matter is suspect to me because of two distinct questions: We know that gravitational wells like that of massive stars do in fact slow the light coming from them to some degree. ...

### 1 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 ...

### 3 “Mass Discrepancy-Acceleration Relation” in ΛCDM Paradigm

Rotation curves of galaxies seem to require more mass than observed - the conventional solution is the introduction of Dark Matter. Reading some articles on this topic (in particular a recent ...

### 4 What are the proposed models for the existence of bars in galaxies?

2 answers, 150 views astrophysics galaxies stellar-dynamics
What are the current explanations and models for the formation of a central bar in some galaxies, and what is the difference that can produce a barred galaxy instead of a spiral one ?

### 2 What does a redder galaxy mean?

I've been reading on the subject and I've repeatedly read that red galaxies are those with redder stellar populations which means (according to my readings) older star populations, with low star ...

### 2 Does the large red shift value of galaxies mean they are far away?

2 answers, 2.174 views cosmology galaxies space-expansion
When the red shifts of galaxies are large, why do we think that they are far away? I know about Hubble's law, Tully-Fisher relation of spiral galaxies, Faber-Jackson relation of elliptical galaxies,...

### 2 Do the arms of a spiral galaxy spin around like a candy bar in long spirals?

Because the arms of a spiral galaxy have a cylindrical-linear center, perhaps they have a cyilindrical rotation around their center same as a vortex of smoke? Have similar movements within galaxies ...

### 6 Astronomical sources of muons

I am looking for some sources of muon particles (μ) in astronomy. By this, I mean I am interested in any astrophysical event where theoretical presence of muons is suggested. For instance, does the ...

### 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 ...

### 1 Can a super-duper massive black hole eventually eat an entire galaxy?

Might there be some roaming black galaxies out there eating up other galaxies?

### 7 Does the dark matter halo rotate with the galaxy?

If the dark matter halo is stationary related to the arms of the galaxy then tidal effects should slow the galaxy rotation. If it rotates with the normal matter in the galaxy then shouldn't it ...

### 1 Amount of Information of a Galaxy? [closed]

1 answers, 57 views astrophysics galaxies information
Just like the title suggests, how much data/information does a galaxy have in (bits)? Like the Milky Way galaxy for example?

### 7 Why the red-shift of distant galaxies is considered to be the effect of expanding spacetime?

Why it's not explained just by Doppler redshift caused by faster movement of those galaxies billions of years ago when that light was emitted? Would the speeds of the galaxies necessary for Doppler ...

### 16 How did we 'discover' dark matter? [closed]

I'm an astrophysics student and I've been researching this topic and there is one point that keeps eluding me. How did the scientific community realize that there had to be dark matter in the ...

### Why can't the Higgs vacuum energy clump to galaxies and act as dark matter (instead of dark energy)? [closed]

The Higgs field has a nonzero vacuum expectation value which contributes to the energy density of the Universe. Energies contribute to the curvature of spacetime and affected by gravitational ...

### 2 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 ...

### 5 What is the evidence that distant galaxies are moving away from us with speeds greater than $c$, due to space expansion?

I came up with this query after @Rob Jeffries's answer to a previous question of mine. So, is there any evidence that distant galaxies are moving away from us with speeds greater than $c$, due to ...

### 3 Why are there no more galaxies moving as relativistic speeds?

Introductory note: I am not discussing galaxies that are going away from us or that are at the border of the universe. If there are no preferred frames of reference, no galaxy or matter ensemble can ...

### 1 How to use parallax and Cepheids together to measure distances?

I can't quite grasp the simple version of how the Cepheid method uses the parallax method to measure the distance to distant galaxies. What I know is that Cepheids exhibit a period vs luminosity ...

### 1 How to use a galaxy's redshift to measure its distance

1 answers, 106 views astrophysics galaxies distance
I know how we can use the spectrum emitted by a galaxy to measure whether it is redshifted/blueshifted, but out of curiosity, how can the redshift of a galaxy be used to determine its distance from us?...

### 1 Article presenting first evidence for dark matter?

What are the papers where the first evidence for dark matter related with the stability of galactic discs, and the orbits of galaxy satellites?

### 2 How do we know that galaxies are not in the process of flying apart?

A major reason for believing in the existence of dark matter is that the stars in the outer regions of galaxies are moving too fast to remain bound to their galaxies, given only the estimated mass of ...

### 6 Why doesn't the light from galaxies appear stretched? [duplicate]

Maybe it's my ignorance of astrophysics/cosmology, but I have been wondering this: Why do galaxies not appear stretched when we observe them? Assuming a galaxy that we observe is 100,000 light years ...

### 2 What is Cosmic Downsizing?

I've had a quick look at a few lecture pdfs and papers as supplementals to my own given lecture notes, but I can't seem to get a proper explanation for what cosmic downsizing is. The closest ...

### 36 What is the evidence for a supermassive black hole at the center of Milky Way?

Black holes cannot be seen because they do not emit visible light or any electromagnetic radiation. Then how do astronomers infer their existence? I think it's now almost established in the scientific ...

### 2 Intuitive understanding of the virial radius/mass

1 answers, 50 views cosmology galaxies virial-theorem
I'm currently trying with no avail to understand the intricacies that define the virial radius or mass in a way that is different from the actual galactic radius/mass. I understand it is derived in ...

### In theory, can we count every galaxy in the observable universe one-by-one?

Suppose I have a very advanced telescope that can detect long wavelengths of light, so I can deal with extreme redshift. I am also a very quick counter, so I can get through all of the galaxies before ...

### 3 Understanding the tidal force tensor

I'm just looking to gain a basic intuitive understanding of the forces at work in tidal stripping and their direction/motivation etc. I'm struggling to grasp the underlying principles and it is making ...

### 1 Mass-to-light ratio and rotation curve from brightness profile

This should probably be basic but I've been looking for days and I can't find how to (I'm probably over complicating, but still). I want to calculate a rotation curve for some spiral galaxies. From ...

### 3 Do AGN produce protons that are relativistic enough to collide with the CMB and make pions?

AGN (Active Galactic Nuclei) produce protons in their jets and they are relativistic. I was reading about photo-pion production, where a proton and photon annihilate to produce a pion. Could this ...

### What is the meaning of 'systemic velocity' of galaxies?

I came across the term systemic velocities of galaxies. Can you please explain what it means?

### -1 What models do physicists use in predicting the movement of stars in a galaxy that has lead to a wide-spread conviction that Dark Matter exists?

My (possibly poor) understanding of the argument for Dark Matter's existence is that stars in a large galaxy move more slowly than "they should" (presumably due to either some simplified model of the ...

### 4 The Sun's Orbit - Is it What We Think?

I was thinking that the sun must orbit something within our spiral arm in the Milky Way, or be affected by other astronomical bodies - surely not just the supermassive black hole centre. I have ...

### Estimating the age of the Fermi Bubbles

Assuming the Milky Way’s Fermi Bubbles were caused by a single event near the galactic center, what are the limits to when that event could have happened? The bubbles reach 25,000 light years high, ...

### 2 What is the current shape of the Milky Way?

1 answers, 88 views astrophysics galaxies milky-way
The things in the universe which are thousands of light years away from Earth can be seen or pictures can be taken by Hubble Telescope because those stars, galaxies etc emitted light thousand, ...

### 4 Is the gravitational effect of distant galaxies lost forever?

Hubble's law is usually expressed by the equation $$v = H_0D$$ According to this equation, the space between us and very distant galaxies, is expanding with a speed greater than the speed of light ...

### 4 New observation of a Galaxy without dark matter: what is(are) the implication(s)?

1 answers, 135 views cosmology astronomy dark-matter galaxies
This recent paper in Nature (also see here$^1$) claimed to have discovered a galaxy without dark matter. However, in the Standard paradigm of cosmology dark matter played a crucial role in the ...

### Are galaxies merely groups of nearby stars that collected together, or do they have a central 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 ...

### 1 Is there a relationship between a stellar-mass black hole and its host galaxy?

0 answers, 34 views black-holes astrophysics galaxies
Out of curiosity, are there any relationships between stellar-mass black holes and their host galaxy? I am asking because I have read about how there is a relationship between a supermassive black ...

### 2 Convert from Relative Magnitude to Mass

I have data which gives me the magnitude density (${\rm mag}\,{\rm arcsec}^{-2}$) of M31 as a function of radius. How can I convert these data to the (enclosed) mass at a given radius (for velocity ...

### -1 Sun-path on the sky [duplicate]

2 answers, 43 views gravity earth sun galaxies
We are standing on the Earth and we see Sun on the sky. We see it walking in a certain direction, with predictable moving. Earth is a spheroid, as we all know. It is circling around the Sun, and also ...