Massive systems held together by gravitational attraction, consisting of stellar associations, star systems, star clusters and types of interstellar clouds, stellar remnants, gasses, cosmic dust and an important but not yet completely understood component called dark matter.

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8
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3answers
109 views

Gross “temperature” of a globular cluster

Globular clusters can be very large, which means we can do statistics about the stars in them. And that means we can try matching their star-as-particle potential/kinetic energy distribution against ...
10
votes
1answer
1k views

If matter and antimatter repel, how do we know other galaxies aren't made of antimatter? [duplicate]

Wikipedia's article on antimatter says this: There is considerable speculation as to why the observable universe is composed almost entirely of ordinary matter, as opposed to a more even mixture ...
0
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0answers
44 views

Gravity's effects on time

So, in the movie Interstellar they say that one year by the black hole is about 35 years back on Earth (excuse any lack of accuracy in the numbers, I haven't seen the movie in over a year). Now, the ...
2
votes
1answer
32 views

Stars more affected by gravity of stars further away, need help understanding argument why

In the first chapter of Binney and Tremaine's "Galactic Dynamics" there is a statement that I don't yet understand. The first chapter of the book is linked here, straight from the publisher. The ...
3
votes
0answers
56 views

Binding energy of a galaxy?

I'm a novice in physics and new to the forms, so please forgive me if this is a dumb question or if this is in the wrong section to be posted, but how would one find the gravitational binding energy ...
1
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2answers
74 views

The force causing galaxies to accelerate away from each other?

The galaxies in the universe appear to be accelerating away from each other according to the Doppler shift that is present in the light we receive from other galaxies. According to Newtonian ...
3
votes
1answer
47 views

Frame dragging resulting in an orbital plane?

In astrophysics today we talked about spinning black holes, ring singularities, and frame dragging. Is this also (to some degree) the cause of the milky way being as flat as it is? Does the spin of ...
1
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0answers
24 views

Are my units right in this galaxy acceleration code? [closed]

I'm running a code to find the accelerations of the galaxies in the Local Group (i.e. an N-body simulation), and the code is producing something that I would expect it to. However, since I'm using ...
3
votes
0answers
44 views

Rotational axes of galaxies

The spiral shape is a preferred form for galaxies due to angular momentum, and the axis of rotation indicates a locally preferable orientation for the angular momentum. Why do galaxies in Hubble ...
2
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4answers
73 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?
1
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0answers
20 views

What sets the lower mass limit for dark matter dominated structures?

Large galaxies appear to be dominated by dark matter, as do dwarf spheroidal galaxies with masses of perhaps $10^6 M_{\odot}$. But (as far as I'm aware) there is no evidence for dark matter in ...
1
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0answers
25 views

Where can I find data for the masses/component velocities of galaxies in the Local Group?

I am trying to run an N body simulation to see how galaxies in the Local Group gravitationally interact for my thesis, but I can't find any data for the masses of the galaxies in the Local Group, or ...
3
votes
0answers
29 views

Need help with determining the stellar mass using the NFW profile

My review assignment has a question that asks us to use the Navarro–Frenk–White (NFW) profile to find total mass in the galaxy using $$\rho(R)=\frac{\rho_0}{1+\frac{R}{R_c}}$$ then taking a triple ...
3
votes
1answer
53 views

Questions about shape of dark matter orbits in spiral galaxies

Could someone please describe how are the proposed (calculated) orbits of dark matter? Are they exactly as those of baryonic matter (i.e. spiral), or they are different from those of baryonic matter? ...
-3
votes
5answers
277 views

Is dark matter really there? [closed]

Dark matter has been proposed to explain two phenomena - Uniform velocity curve of spiral galaxies Observed gravitational lensing. If something explains these two, would we still need dark ...
8
votes
1answer
130 views

How many galaxies could be the source of the recent LIGO detection?

The recent LIGO detection is pretty exciting, and a lot of people are asking whether there is a chance of optical detection of the black hole pair that created the signal. From a cursory reading of ...
1
vote
1answer
83 views

Mass and time relativity [duplicate]

In the space between galaxies in the absence of matter, would time run faster than inside a galaxy? A black hole can slow time. Is there a cosmic opposite of that effect on time? Like the following ...
0
votes
3answers
112 views

If our eyes see at the speed of light, how do we know about the current states of stars and galaxies far away?

As you guys know that we see at the speed of light, it means that we see the past of stars and galaxies. So say a star went supernova right now, how are we able to know current state of that star that ...
1
vote
0answers
30 views

How to determine the size of other galaxy's/The dark matter problem

From what i understand there are two methods (well as far as i know) to determine how much mass there is in a distant galaxy. First, Luminosity. By measuring the amount of light produced from a ...
1
vote
1answer
74 views

What is the limit of the deep field exploration?

The deep field exploration is quite fascinating, first the Hubble Deep Field (HDF) showing a small piece of the Univers one billion year after the Big-Bang, next the Hubble Ultra-Deep Field (HUDF), ...
0
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0answers
40 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
1answer
94 views

Bigger Galaxies = Faster Clocks [closed]

There are in all about 100 known galaxies with blueshifts out of the billions of galaxies in the observable universe. We have Blue-shifted galaxies are in our own local group, and are all bound to ...
2
votes
3answers
108 views

How big bang could produce later collisions

The Milky Way and the Andromeda galaxies are supposed to "collide" in 4 billion years (collide in the sense of overlapping space, but nothing is really supposed to contact anything else). Assuming: ...
2
votes
0answers
38 views

Visible Mass Distribution in a Galaxy [closed]

Is there any known relationship between stellar density and distance from the galactic centre? I want to know how the visible matter is distributed in the galaxy, especially at the bulge.
1
vote
1answer
45 views

Why do distant galaxies (quasars) look white in photos?

My question is inspired by this question about red shift. When viewing photos of distant galaxies, especially quasars, they are often shown as white. However, the light would have been red-shifted. ...
9
votes
3answers
237 views

Coupling between galaxy spin and central black hole spin

What is the relationship between the spin of a galaxy and the spin of its corresponding black hole? Associated questions: Do they always have the same axis of rotation? Do they always spin in the ...
1
vote
1answer
55 views

Eccentric binary black holes

Comparable-mass binary black hole inspirals and mergers are expected to be an important source of gravitational wave signals for current and future ground-based detectors. It is generally expected ...
8
votes
1answer
768 views

The final parsec “problem”

Many and perhaps all galaxies seem to contain supermassive black holes of about $10^7 M_\odot$ at their centres. Determining their origins is of great astrophysical interest. In what I understand to ...
3
votes
0answers
35 views

Why is the galaxy's dark matter halo a sphere instead of a disk? [duplicate]

I understand that the galaxy is disk shaped because it has a substantial total angular momentum (if that's the right term). If the dark matter halo is a sphere, does that mean that its total angular ...
2
votes
2answers
185 views

Does Newtonian physics work on a galactic scale?

I'm currently working on a simulation that aims to use Newton's Law of Gravitation to simulate how a galaxy behaves gravitationally. While I haven't gotten the simulation finished yet, I have had a ...
1
vote
0answers
16 views

Astrophysics of spirals [duplicate]

What accounts for the structure of spiral galaxies? I would seem that, considering gravity is proportional to distance, outer objects could not be connected in any way to inner objects (ie. a spiral) ...
39
votes
2answers
7k 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 ...
0
votes
3answers
156 views

What part of the Milky Way do we see?

I have seen several pictures depicting our galaxy, but I would like to clarify the following: Picture 1: Picture 2: What part of the galaxy is depicted in the first picture, which is taken from ...
0
votes
1answer
46 views

How Does Rotational and Turbulent Motion Contribute to the Pressures of Dynamical Systems?

Rotational and turbulent motion can deepen a gravity well in a galaxy or galaxy cluster. In an analysis of the mass components of a large body, this would appear to be one of the components. Does it ...
0
votes
1answer
51 views

How is the total mass of Andromeda determined?

I am currently attempting to use Doppler shifts on both the advancing and receding sides of the galaxy to determine the mass. I am not sure exactly how I would convert the advancement and recession ...
3
votes
2answers
150 views

Why is “gravitational” red-shift neglected in galaxy and galaxy cluster scales?

The red-shift of the light of a star in a galaxy or that of a galaxy in a cluster of galaxies is generally interpreted as how fast the star or the galaxy is moving, i.e. it is interpreted in a purely ...
1
vote
0answers
49 views

Cumulative mass & mass distribution of a disc galaxy

Hernquist has a great formula to represent the cumulative mass of a spherical galaxy (8): http://star-www.st-and.ac.uk/~hz4/contempastro/hqm.pdf 1) Is there any simple formula for disc shaped galaxy ...
1
vote
0answers
20 views

Do clocks near the centre of the galaxy run slower than clocks at the edge? [duplicate]

Does an astronaut floating in space near the center of the galaxy, where the mass density is higher (let's ignore the dark matter halo for this example) have a clock that runs slower than an astronaut ...
2
votes
0answers
57 views

Bulge-Disk decomposition in galaxies

I'm starting a new project on dark matter astrophysics in which I have to extract from some data (I will write some below) the surface brightness, to later construct the mass density profiles of de ...
0
votes
0answers
33 views

Explanation for Spiral galaxies [duplicate]

Can anyone explain to me why our galaxy is spiral and not irregular or spherical? Please be specific and if maths is required to state what you mean precisely, use it. I will understand it much better ...
0
votes
1answer
158 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
85 views

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 ...
0
votes
1answer
53 views

NED vs. SIMBAD: Which is more accurate?

I'm doing some research on M33. NED lists the luminosity as 6.27. SIMBAD gives it as 5.27. First, it looks odd to me that the difference is exactly 1. Second, I've seen other differences comparing ...
52
votes
4answers
5k views

Do solar systems typically spin in the same direction as their galaxy?

Is the net angular momentum vector of our solar system pointing in roughly the same direction as the Milky Way galaxy's net angular momentum vector? If yes or no, is that common for most stars in the ...
4
votes
0answers
91 views

Relation between dark matter and supermassive black holes located in the center of galaxies

This research (see link), conducted on 3000 elliptical galaxies (which are typically galaxy merger results), reports finding "distinct relationship between the mass of the dark matter halo and the ...
0
votes
2answers
43 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
0answers
22 views

Rotating Direction of spiral galaxies [duplicate]

I am engineer working on some different mechanical tests with spiral shapes. My question are spiral galaxies trailing or facing. I have try to find out on internet but look to me that is not quite ...
0
votes
1answer
83 views

Green function for Fourier transform [closed]

In the context of a project, I had to solve numerically Poisson equation with cylindrical coordinates. I put here results for z = 0 on a 3D mesh 256x256x256. When I define Green function, have I to ...
0
votes
0answers
23 views

Do the arms of spiral galaxies differ based on the speed of which the galaxy is rotating?

If I were to take a circle with strings attached to it and spin it, the strings would behave differently based on how fast the circle is rotating. Do galaxies behave the same way?
1
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2answers
92 views

Before we realized that supermassive black holes were at the center of large galaxies, how did the models explain galaxies?

So, I was watching this show on Netflix about supermassive black holes. I didn't realize that astronomers were surprised to find these black holes at the center of galaxies, because I cannot imagine ...