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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Dark age of the universe

during the early universe and just after the habitable epoch,when the universe was finally cooled down allowing the ions to recombine into atoms, comes the Dark Ages who are currently thought to have ...
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54 views

Do gamma ray bursts play a role in cosmic evolution?

If gamma ray bursts were to interact with gas clouds in the early universe, might it be a relevant factor in star production?
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678 views

Do quasars exist today?

Are there likely to be any quasars right now, or are all the ones we're seeing old galaxies today, like the Milky Way?
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1k 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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1answer
30 views

Galaxy bias and baryon acoustic oscillations (BAO)

I have a doubt with the concept of galaxy bias and how it affects baryon acoustic oscillations, it is supposed to mean that by measuring the distribution of galaxies we are not measuring the actual ...
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2answers
3k views

What does a galaxy orbit?

Moons orbit planets, planets orbit stars, and stars orbit the center of a galaxy. So, my question is what does a galaxy orbit? The center of universe? (I know that the universe has no center)
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Why the galaxies forms 2D plane (or spiral-like) instead of 3D ball (or spherical-like)?

Question: As we know, (1) the macroscopic spatial dimension of our universe is 3 dimension, and (2) gravity attracts massive objects together and the gravitational force is isotropic without ...
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2answers
95 views

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 ...
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123 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 ...
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1answer
61 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 ...
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1answer
18 views

numerical galaxy morphology classification scheme

For an assignment, I've been told to divide up the galaxies with a Virgo Cluster Catalog number into early and late-type galaxies using the GOLDMine database, http://goldmine.mib.infn.it:8080/ ...
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2answers
7k views

How could scientists know how far a star or galaxy is from us?

How do astronomers measure how far a star (or galaxy) is away from the earth? How would they know that it has taken 13 million years for light to travel in space before it reaches us?
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84 views

Olbers Paradox Solution

Olbers’ Paradox says that in an infinite universe every line of sight will end on a star. Surface brightness is independent of distance (moving a star further away makes it smaller and reduces its ...
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116 views

What will happen to the Earth when Milky Way and Andromeda merge?

Hypothetically, if our solar system survived into the far future and human was still around, is the merge between 2 galaxies were a disaster for lives on Earth? Were the Sun get thrown away from the ...
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524 views

How does color of galaxies explain their distance?

Why do distant galaxies have different colors than closer ones?
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41 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 ...
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3answers
2k views

What are galactic speeds measured against?

The Earth moves through space at 67,000 MPH. The Milky Way travels through a local group at 2,237,000 MPH. Wouldn't you need a fixed point to be able to measure velocity against? After all, compared ...
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0answers
19 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 ...
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764 views

How do spiral arms form?

Why aren't all spinning galaxies shaped as discs as my young mind would expect? I understand how the innermost parts of a galaxy spin faster than the outer parts, and that could explain why some ...
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1answer
85 views

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 linear center, perhaps they rotate around their center same as a candy bar spiral or a spiral of smoke? Have similar movements within galaxies been measured? ...
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Why the center of our galaxy doesn't absorb us?

Depending on the theories, the center of our galaxy is a super massive black hole, this is easy to accept as a truth, but what I couldn't simply devour is how the solar system is orbiting around it ...
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1answer
40 views

Tidal tails of galaxies after collision

When there is a collision of 2 disc shaped galaxies, there is a tail formation created from both the galaxies. I read here that this was due to tidal forces, but I couldn't figure out how this ...
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2answers
63 views

Mass of NGC 1097 Galaxy

I've been looking all over the internet for this and can't seem to find a reference. Can anyone refer me to a paper citing the mass of NGC 1097 based on luminosity?
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55 views

Why is the lyman alpha line asymmetric at high redshift?

If someone could explain this to me I'd be very grateful, thanks.
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1answer
66 views

What is the limit for the size of a galaxy?

The largest known galaxy is just 100x more massive than Milky Way. I wonder if there is some physical mechanism (some equilibrium) which limits the size of galaxies or if it is just because of limited ...
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Experimental Data for Mass Distribution of a Galaxy

My goal here is not to discuss dark matter in general. I know there are many other observational clues that hint us towards Dark matter. My goal is simply to understand this argument here a little ...
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Is there a binary black hole system in the middle of the galaxy?

We have observed gravity effects from black holes in the center of galaxies, but galactic centers are dusty so we can’t tell if it’s one black hole or two black holes in a binary system in there. A ...
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Do green stars exists?

I asked a university lecturer why we don't observe green stars, and he said the blackbody curve averages at that frequency such that the cones in our eyes don't recognise it. I have a hunch that ...
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Distribution of dark matter in galactic halos

Often dark matter around galaxies is referred to as a 'halo'. I've seen the galactic rotation curves, but I'm having trouble visualizing how the dark matter is distributed for a typical rotating ...
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354 views

How to tell if a star is in a galaxy?

An astronomer is studying a star that appears to be in a galaxy. How does the astronomer know the star is actually in the galaxy and not just on the same line of sight as the galaxy? I'm guessing ...
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45 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 ...
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1answer
79 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 ...
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2answers
127 views

In a random direction, am I more likely to find a dwarf or giant galaxy?

First a couple of disclaimers: My title explains the idea of my question, but I will pose it slightly differently to make it less subjective. This ends up being in the style of a homework exercise ...
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1answer
332 views

Difference between Gunn Peterson trough and the Lyman Alpha Forest? Cosmological implications?

I'm having difficulty understanding the full implications of the Lyman alpha forest and its use in cosmology. My understanding is this: we detect features in the Intergalactic Medium (IGM) by very ...
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1answer
114 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?
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CMB parameter, what's the meaning of the matter power spectrum normalization sigma_8?

Most CMB experiments like WMAP and Planck include a certain cosmological parameter called $\sigma_8$. My understanding is that normalization of the matter power spectrum is not a theoretical ...
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65 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 ...
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2answers
94 views

Why has the amount of star formation in the Universe decreased over time?

If you like, refer to my old question from the last year, about star formation rates and their declining, answered by Rob Jeffries. I'm now examining why this process happens. It appears that in ...
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0answers
50 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 ...
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2answers
765 views

What is a reasonably accurate but simple model of the Milky Way's gravitational field?

I am putting together a toy program which shows how stars move around in the galaxy. To run the simulation I need to know strength of the Milky Way's gravitational field at any location in it. I'm ...
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2answers
892 views

How did we find out the shape of our own galaxy without going out of it?

As far as I know, scientists have been able to see a lot of differently shaped galaxies in our visible universe through modern age telescopes. But I was wondering how it was possible to know how our ...
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1answer
43 views

Can invisible galaxies exist? [duplicate]

Is it possible that there are newly formed galaxies which are moving so fast that we will can't see them, even though they exist "inside" our visible universe? I've been wondering if this could be a ...
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1answer
29 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 ...
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2answers
2k views

Why isn't the center of the galaxy “younger” than the outer parts?

I understand that time is relative for all but as I understand it, time flows at a slower rate for objects that are either moving faster or objects that are near larger masses than for those that are ...
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1answer
51 views

Relativity and Galaxy Rotation Speed

If time travels slower nearer gravity wells, why can't the galaxy rotation speeds being faster on the outer edges than the inner areas be explained by relativity? What necessitates dark matter?
6
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1answer
118 views

Do the stars in a galaxy have a thermal kinetic energy distribution?

I think, there is practically everything given to that: many point-like masses, able to exchange energy pseudo-randomly, and far long enough time to reach a thermodynamical equilibrium. Of course, ...
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5answers
7k views

Why aren't there spherical galaxies? [duplicate]

According to the Wikipedia page on Galaxy Types, there are four main kinds of galaxies: Spirals - as the name implies, these look like huge spinning spirals with curved "arms" branching out ...
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2answers
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Can we solve most of the cosmological questions using the Illustris universe simulation?

The Illustris project (http://illustris-project.org) attempts to simulate the universe in its most accurate form according to their website. With the simulation, they were able to predict the neutral ...
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2answers
144 views

Why are galactic centers always brighter than the edges?

As you can see the image below and other galaxy images, the center is generally much brighter. Why is that? Is there a very big star? A very big gravitational field?
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2answers
617 views

Why is the Milky Way flat? [duplicate]

I read recently that the galactic "flatness" of the Milky Way is due to the rotation of the galaxy combined with a vast stretch of time. Yet, I also read where 1) the Milky Way rotates once every 225 ...