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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How and why will the Milky way collide with the Andromeda?

Hubble's law says that the universe is expanding.How come the milky way and the andromeda are on a collision course?How will they end up colliding with each other?
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Can the “Milky Way” galaxy be seen by the naked eye in a clear sky?

Is this photo "real"? Are the stars not super-imposed in the image?    
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2answers
1k views

Formula for Rotation curves of Galaxies

To ask a more specific one for the rotation curves of elliptical galaxies, and hope from there to later understand the dynamics of spiral galaxies. Treating the galaxy as an isothermal ...
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6answers
7k views

Why are some galaxies flat?

What is the explanation for the flatness of some galaxies? (If it's due to their rotation then why they are rotating, why some other galaxies are not flat etc., I would like to hear a nice and ...
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1answer
132 views

Galaxies seen from Earth

If we observe two galaxies from the Earth that are diametrically opposed and each 10,000 light-years from the Earth, will the separation distance between the galaxies be 20,000 light-years? ...
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1answer
56 views

Why is the measured distance to the Triangulum Galaxy much more uncertain than to the Andromeda Galaxy?

Why is the measured distance uncertainty for M33 (835 ± 105 kiloparsec) six times bigger than the measured distance uncertainty for M31 (778 ± 17 kiloparsec)? They are approximately at the same ...
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1answer
158 views

two distant galaxies seen from earth

From the Earth If we observe two galaxies that are diametrically opposed and each 1000ly far from the earth. the separation distance between the galaxies will be 20000ly? really question is: if the ...
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1answer
214 views

How are galaxy filaments formed? And do they have any analogues in stellar formation?

In physical cosmology, galaxy filaments, also called supercluster complexes or great walls, are, so far, the largest known cosmic structures in the universe. They are massive, thread-like ...
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1answer
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Most accurate ways to find the average distance between stars in Milky way galaxy

I've already posted here on quora. But, I'm not totally sure if it's the most reasonable method. Would anyone care to elaborate on how to find the average distance between stars in a given galaxy ...
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1answer
92 views

Do red galaxies have red star-lit skies?

I noticed when looking at some deep space pictures, like the Sombrero Galaxy (M104) or the Hubble Deep Field (HDF), I see galaxies of various colors. Does that mean, for instance, than any inhabitant ...
3
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1answer
39 views

What determines a progenitor's fate as a spiral or elliptical?

I was thinking about my answer to Are the inner planets on planar orbits because there was more dust in the inner solar system (early on in planetary accretion)? - when it occurred to me that maybe I ...
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3answers
138 views

Did I see two Milky Ways next to each other?

I am from the northern hemisphere and as far as I remember, the Milky Way was "single lane", just one stripe. At least, this is what I recall the Milky Way to look like when seeing it from near ...
2
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1answer
525 views

$N$-body simulation in General Relativity

How would one perform an $N$-body simulation in General Relativity (GR) for something like galaxy formation or galactic dynamics? Suppose one wants to simulate the rotation curve $v(r)$ for galaxies ...
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4answers
611 views

What does ionization of neutral Hydrogen have to do with “transparency”?

Most accounts of the early history of the Universe make some reference to (re)ionization as being the reason that the Universe becomes transparent after a period of opacity caused by the absence of ...
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3answers
877 views

Are we capable of discovering planets in the Andromeda galaxy?

I just watched this SpaceRip video on YouTube which shows pictures taken by Hubble while looking into the disk of the Andromeda galaxy to study a certain type of variable star. It occurred to me that ...
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3answers
65 views

Can the Hanbury-Brown and Twiss effect be used to measure the size of composite objects like galaxies?

I know that the Hanbury-Brown and Twiss effect can be used to measure the size of stars. Can it also be used to measure the size of galaxies?
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6answers
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Why is the universe so organized?

If you think about the Big Bang and the flow of matter in all directions, you would think, how unorganized would this universe be? No matter how long it would take. The idea that matter or most of it ...
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3answers
84 views

What keeps galaxies united like a solar system?

Blackholes may be really strong but they act in a very short range. For example if the sun was a black having the same mass, it will be dark but we will still be revolving around it. It wont engulf ...
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3answers
2k views

How would we tell antimatter galaxies apart?

Given that antimatter galaxies are theoretically possible, how would they be distinguishable from regular matter galaxies? That is, antimatter is equal in atomic weight and all properties, except for ...
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3answers
1k views

Solar system, visible stars and deep sky objects

Since I've seen that galaxies are often called "deep sky objects", as opposed to individual stars, does this mean that all visible stars in the night sky actually only belong to The Milky Way Galaxy? ...
6
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1answer
121 views

Stellar Viscosity in Galaxies

Is there such as thing as the viscosity of stars in a galaxy, along the lines of gravitational attraction between stars changing the dynamics. If so, how is that put in terms of the Virial Theorem?
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2answers
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Mass of a galaxy via luminosity

Is there a general formula for calculating the mass of a galaxy, or even a nebula from the luminosity? Or, is there a way of calculating the total mass of a galaxy from its energy output? Is there a ...
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1answer
245 views

Mass of a galaxy via Luminosity [closed]

Is there a way of calculating the mass of a galaxy, or even a nebula from the luminosity? EDIT I'm deleting this, and moving the question to Astronomy Stack Exchange - thanks david
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4answers
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How to find the Andromeda galaxy without using a go-to telescope?

In other words, what is the proper technique (star-hopping or other?) in order to find and properly point a telescope to this target? Would a star atlas or other tool/reference help? Can I use the ...
18
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2answers
412 views

How would the night sky appear at the edge of the galaxy?

In Isaac Asimov's Foundation Series, there is a planet named Terminus which is believed to be the planet farthest from the galactic center. There are almost no visible stars in its sky, only the ...
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3answers
212 views

What frame(s) of reference are used to measure the rotation of the Sun around the galaxy ?

I can find various speeds and estimated durations listed at numerous places but none specifically describe the frame of reference. Possible options as example of kind of answer I expect. Local ...
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3answers
165 views

Shapes of galaxies

I've heard most of galaxies are spiral or ellipsoid shaped. Is it true? If true, then why they form in such shapes? How did arms of the spiral galaxies form?
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2answers
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What happen when two galaxies collide?

As the title suggests, I know collision of galaxies happens. Questions are Why do they collide (obviously because of gravity, but in what conditions)? Aftermath of the collision? If there is a super ...
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3answers
121 views

What's dark matter and who discovered it?

I have heard about dark matter that's called the Master Of The Universe. What's this and is the dark matter the reason galaxies exist?
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4answers
345 views

What is the name of our Galaxy?

I was told that the name 'Milky Way' first came about when people observered the milky looking stretch of sky; that is, before telescopes came about and we realised it wasn't a milky cloud, but rather ...
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2answers
4k views

How many stars are in the Milky Way galaxy, and how can we determine this?

I have heard multiple estimates on the quantity of stars within our galaxy, anything from 100 to 400 billion of them. The estimates seem to be increasing for the time being. What are the main methods ...
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2answers
387 views

How can a spiral galaxy exist?

A spiral arm orbiting a central mass should be dispersed quite quickly as the outer elements would move more slowly than the inner ones. The Milky Way, is about 59 Galactic Years old, which, one would ...
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1answer
121 views

Baryonic Missing Mass

A recent article from a popular astronomy website tells of discovery of missing mass (not dark matter) that has puzzled astronomers for some time. Apparently, the discovery involves enhanced electron ...
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3answers
214 views

What is the strange event in this simulation of a galactic collision?

I was watching this video on YouTube: 2 Spiral Galaxies w/Supermassive Black Holes Collide Around half way, and again almost at the end, the black holes seem to suddenly give off some sort of force ...
3
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1answer
188 views

Gamma Ray Bubble at the center of our galaxy seen by Fermi Telescope

How could we measure high energy photons, whithout measuring them ? I can't understand how we can "see" those Gamma Ray Bubbles if they are not reaching here In this graph from Nasa you can see ...
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1answer
337 views

How is the mass of black hole at the center of our galaxy measured?

I've been watching a video about dark mater and a lot of the mass is missing in our universe. Astronomers got to this by measuring the speed that stars orbit the center of the galaxy and when they did ...
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1answer
1k views

Why do galaxies and water going down a plug hole spin?

We all experience things spinning, whether it's water down a drain, the earth on its axis, planets round the sun, or stars in a galaxy - even electrons round an atom. But why is spin so common in ...
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5answers
933 views

Is there a black hole in the centre of the Milky Way?

Is it true that the whole galaxy is actually revolving, and powered by a black hole? Has it been proven, and if it is true, how can our solar systems actually keep up the momentum to withstand the ...
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2answers
200 views

Does the recent re-count of stars in elliptical gallaxies affect our understanding of the universal mass balance?

I've seen several popular reports of a new count of low-mass stars in elliptical galaxies (here's one). Edit: Pursuant to several correct comments I've changed the title to agree with the actual ...