Questions tagged [galaxies]

Galaxies are gravitationally bound systems of stars, interstellar gas and dark matter, often hosting a central supermassive black hole. For questions about the structure, composition, dynamics, classification, etc. of galaxies. This includes small systems of interacting galaxies (i.e. merger, or galaxy + satellite system), but for galaxy groups and clusters use [galaxy-clusters], and for questions specific to our own Milky Way galaxy use [milky-way].

Filter by
Sorted by
Tagged with
0
votes
1answer
71 views

Where is the mass and gravitational influence of dark matter? [duplicate]

I'll have to ask an elementary level question about orbital motion and the mass/gravity that influences it. In solar systems, the large mass of the sun pulls on the planets and we see the velocity of ...
0
votes
1answer
143 views

Why does most galaxies resemble a 2 dimensional plane? [duplicate]

Older galaxies mostly tend the revolve forming a disk. Why are the stars not revolving around the center of the galaxy like a sphere instead similar to electron in an atom?
0
votes
2answers
94 views

What is the maximum of information in a beam of light?

If I look at the space I can see the Andromeda Galaxy as a small dot in the sky. If I look through a telescope, I can see the spiral shape. If the saw right through a huge telescope, I could see a ...
0
votes
1answer
703 views

What is the direction of our solar system in the Milky way galaxy and in the universe?

What is the direction of our solar system in the Milky way galaxy and in the whole universe? Are we heading toward another constellation, not including Andromeda?
0
votes
1answer
162 views

How many galaxies in the observable universe have we counted and mapped?

I could find any sources. How many galaxies are counted, named and mapped? How many more there are to be mapped in the future(the total count)? Are there galaxies in the observable universe that ...
0
votes
1answer
51 views

Expansion of Galaxy's Caused by Electromagnetic forces

From my limited physics knowledge i know that gravity when compared to Electromagnetic forces is very weak... So if every object is polarized (positive and negative separation), then on a bigger level ...
0
votes
1answer
26 views

View from inside clashing galaxies

The below image from Hubble show two clashing galaxies. Is there a simulation (or whatever) as how the sky would look withing those galaxies? For example, would the night sky be noticeably brighter ...
0
votes
0answers
22 views

Where can I find the star distribution data of our galaxy?

I am doing some research on dark matter and for that I need data of star distribution in our Galaxy. Is there any mathematical law that predicts the distribution pattern of stars in our Galaxy?
0
votes
0answers
27 views

Generally how much faster are stars on the outskirts of galaxies orbiting than they should be?

This assumes there is no mysterious matter causing the extra speed. Are they orbiting say 10% faster than expected etc?
0
votes
0answers
30 views

Texts on Hoag's Object

Are there any good texts online that someone can recommend on Hoag's Object? It is a very weird galaxy and I would like to learn more.
0
votes
0answers
15 views

How well supported by observations is the hypothesis that concentrations of dark matter are essential to galaxy formation?

Much work regarding the formation and early evolution of galaxies seems to assume that galaxies form based on clumps dark matter. The following observations indicate that some galaxies started with ...
0
votes
0answers
37 views

Gravitational redshift and mass decrease

If there are two distant gravitationally unbound galaxies and the observer galaxy loses its mass twice faster than the distant galaxy. So gravitational blueshift decreases in the observer galaxy. ...
0
votes
0answers
15 views

How do Oort's constants relate to shear and vorticity?

I am told to show that Oort's constants represent shear and vorticity in the velocity field of an orbiting star. I know that Oort's constants are defined as: $A = \frac{1}{2}(\frac{v_{\bot,0}}{R_{0}}...
0
votes
0answers
62 views

Gravitational potential energy of an isothermal sphere

I am trying to calculate the gravitational potential energy, W, defined as: $W = -\frac{1}{2}\int\rho(r)\Phi(r)d^{3}r$ for an isothermal sphere. I am given that the density profile varies with r as:...
0
votes
0answers
38 views

Jeans equation for a fully isotropic velocity dispersion tensor

Given a known spherically symmetric gravitational potential, $\Phi(r)$, I need to calculate the value of the velocity dispersion tensor $\sigma_{rr}$. To calculate $\sigma_{rr}$ I am using Jean's ...
0
votes
0answers
39 views

Does dark matter experience drag?

Is dark matter dragged around the galaxy by gravity as stars and groups of stars orbit the galaxy, and, if so, is its shape/distribution deformed? Similarly, would the Oort cloud be deformed by being ...
0
votes
1answer
59 views

Could space repel mass?

I'm not an advanced physics person, so any explanations need to be reasonably low-level... I was looking at oil/water bubbles (hydrophobic vs hydrophylic molecules) and it got me thinking about the ...
0
votes
1answer
37 views

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 ...
0
votes
1answer
60 views

Estimating total mass inside the Sun's orbit

I'm trying to estimate the local density of dark matter at a given radius, $r=R_0=8\text{kpc}$. I also have values for the core radius, $a=5\text{kpc}$, and circular velocity of the Sun, $v_{\text{...
0
votes
1answer
76 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 ...
0
votes
1answer
46 views

Dark matter halo distribution for simple galaxy model

It is a sufficiently well-known fact that the rotation curves of spiral galaxies are approximately flat in the middle to far regions of the disk. This is in apparent contradiction with the fact that ...
0
votes
2answers
89 views

If the Universe is expanding, then why will Andromeda collide with the Milky Way? [duplicate]

Andromeda is moving towards the Milky Way Galaxy at around 250,000 mph, but I wonder what is the direction of our Milky Way Galaxy? Are these two galaxies heading towards each other or Andromeda will ...
0
votes
1answer
180 views

Why does dark matter form a halo, Unlike normal matter? [duplicate]

Hi I am curious to know why dark matter forms a halo? Or why doesn't normal matter form a halo.What is the difference between the two My level is amateur
0
votes
1answer
28 views

Why do galaxies over time become more refined? [duplicate]

Why do galaxies over time become more refined, ordered and defined instead of more random and disordered?
0
votes
1answer
68 views

Galaxy equillibrium

I know this is a very dumb question, but, to maintain a galaxy as a bounded system, the total energy and the total angular momentum of every particle component of the galaxy (suppose made of gas and ...
0
votes
0answers
23 views

About the use of Newtonian Relations for the movement of stars in the Galaxy [duplicate]

From a General Relativity point of view Gravity is given as the result of spacetime curvature interacting with energy-mass density. To get to the Newtonian limit one needs to take a) Non-relativistic ...
0
votes
0answers
48 views

How are planets distributed in elliptical galaxies?

I'm trying to figure out if planets are equally distributed in galaxies (I'm assuming they aren't) or if there is some logic behind their distribution.
0
votes
2answers
127 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 ...
0
votes
1answer
109 views

Shape of galaxies [duplicate]

i want to know why galaxies are spiral in nature.. let us say there is some sort of intense mass (black hole?) at the centre of our milky way galaxy. the intense gravitaional pull is keeping evey ...
0
votes
0answers
29 views

Primordial galaxies and associated mass of blackholes [duplicate]

How could primordial galaxies or quasars at great redshifts like quasar ULAS J1120+0641 (detected as per when the universe was 700 mill years old) have blackholes at their centers with the mass of 2 ...
0
votes
1answer
436 views

Describe a path that a star moves around the sky [closed]

Suppose a star in the ecliptic plane has a parallax of p = 0.5 arcsec and a proper motion perpendicular to the ecliptic plane of µ = 1.0 arcsec/year. I need to describe the path that the star ...
0
votes
0answers
79 views

How does mirror matter account for the faster than expected spin of gallaxies?

To explain dark matter, some physicists have postulated the existence of mirror matter as an alternative to WIMPs, where mirror matter particles could interact with one another in the same way as ...
0
votes
1answer
65 views

Synthesising types of galaxies using various stellar spectra

I have been given the task of synthesising an elliptical galaxy, a starburst galaxy and a spiral galaxy (considering the arms and the bulge separately and adding them) using stellar spectra which I ...
0
votes
0answers
34 views

Space within galaxies. Is it stuck by the gravity of the galaxy or expanding and “slipping past”? [duplicate]

I understand that the inter-galactic space is expanding but galaxies themselves are not. What is happening to the space within a galaxy? Is it fixed by the gravity of the galaxy or is it expanding and ...
0
votes
2answers
200 views

Which direction does a galaxy move in respect to its axis of rotation (Black Hole)

As Galaxies travel through the universe, how do they orient? And, does this orientation apply to stars and their satellites? that is to ask if the movement of a galaxy or star is perpendicular to ...
0
votes
0answers
41 views

Research on galaxy “stiffness”? [duplicate]

Possible Duplicate: Are galactic stars spiraling inwards? Has there been any research on the effects of interstellar gravitational attraction that would make collective star motion in a galaxy ...
0
votes
1answer
93 views

Has galaxy merger and universe expansion been proven?

I understand the basic argument for hierarchical merging of galaxies during expansion of the universe. I also understand peculiar motion and the Hubble flow. So I understand what's going on with ...
0
votes
2answers
614 views

Can one model a spiral galaxy with a similar manifold to one for a whirlpool?

My question is more of a phenomenological question than literal, since the forces involved are very different. When one looks at the distortions (or wrinkles or whatever you wish to call them) in the ...
0
votes
2answers
810 views

How long would it take for a galaxy to collapse without dark matter?

I am trying to understand the effects of gravity in the Cosmos without complications of Dark Matter/Dark energy issues. So my question is, assuming that a galaxy (for example, the Milky Way) does not ...
-1
votes
1answer
171 views

Are all galaxies we see really our Milky Way? Any possibility?

There is a possibility for our universe to be the surface volume of a (higher-dimensional) hyperspace. So if this possibility is true,then is there also a possibility that the other galaxies we see ...
-1
votes
1answer
77 views

Frame Dragging by Sag A star

Is frame dragging by the supermassive black hole Sag A responsible for the milky way's rotation? If so would we also be part of time dilation depending on how close we are to Sag A? Is the gravity ...
-1
votes
1answer
215 views

Percent of spiral galaxies in universe

I want to know wich is the % of the galaxies with stable orbits (I think this are only Spiral ones). cheers.
-1
votes
2answers
50 views

Sun-path on the sky [duplicate]

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 ...
-1
votes
1answer
401 views

Why are galaxies flat since it's an unstable configuration in 3d? [duplicate]

I'll probably have to delete this question because someone's already asked it, but what accounts for the stable 2-d structure of spiral galaxies in three dimensional space (assuming random starting ...
-2
votes
1answer
81 views

Can we see galaxies that tell us what the Milky Way will be like in future time?

When we are looking at any galaxy we look usually at past time. As in case of Andromeda Galaxy we are looking at 2.5 million years back. In the same way do we have galaxy which will show future ...
-2
votes
1answer
61 views

A question about horizontal doppler effect on galaxy hydrogen radiation observation

The figure shows the positions of the solar and neutral hydrogen regions A to D rotating in a circular orbit relative to the center of the galaxy. The sun and A to D assume a Kepler rotation. ...
-3
votes
2answers
179 views

Why can't I see whole galaxies with the naked eye?

I have read these questions: At what distance could you see andromeda with the naked eye? Do all the individual stars that we can see in the night sky belong to Milky Way? I look at the night sky ...
-3
votes
1answer
53 views

Could dark matter be normal matter that is beyond the observational horizon?

As I understand it, matter that is too distant for its light to reach us would not be observable, and the CMB is the limit of what is observable from our location within the universe. Could what is ...
-3
votes
1answer
409 views

What is the percentage of dark matter in the galaxy? [closed]

Assuming the mass of the stars and gas within NGC 5055 is $8\times10^{10} M_{sun}$. What is the percentage of the dark matter in it?
-4
votes
2answers
35 views

Is it possible that galaxies formed from incredibly fast neutron star collisions?

In the recent Kurzgesagt youtube video there is mention of how neutron star collisions are the likely candidates for creating the heavier elements in the universe. It is also possible that it created ...