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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What is a flat rotation curve?

Was reading about dark matter and the distribution of it throughout the galaxy. it said "For example, if rotation curves are flat this means-" what exactly does this mean?
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3k views

Density of stars near the center of the Milky Way

At night, I can look up and see the Milky Way across the sky. My question is, supposing our solar system was, instead of way out on an 'arm' of the galaxy, if we were near the galactic center. Would ...
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3answers
73 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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199 views

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-...
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2answers
98 views

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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2answers
258 views

Galaxies that are newer than our own one

Can we see any galaxies/stars that are newer than our own galaxy? As light takes (c) amount of times to reach us - so relatively speaking, light which would have left the newer galaxy (and far enough ...
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81 views

When will galaxies become unstable due to dark energy?

When will galaxies become unstable due to dark energy? What will it be like for a civilization to observe their own galaxy going through this period of instability?
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598 views

What is the distribution of Population I and II stars in the Milky Way galaxy?

I have been trying to find out the distribution of Population I and II stars in the Milky Way. The distribution I mean is the percentage of each population to the total stars in the galaxy. So in ...
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130 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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209 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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203 views

Thought experiment: Tethered galaxies - to the extreme [duplicate]

If two rocks were tied together with a tight, absurdly long, non-elastic rope, and placed on planets at either end of Earth's observable universe - or beyond - What would happen? Is the structural ...
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2answers
584 views

Accuracy and assumptions in deriving the Tully-Fisher relation

I understand the mathematical derivation of the Tully Fisher relation from basic physics formulas, as shown on this site. However, after using the physics equations, it seems that several assumptions ...
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37 views

Maximum “size” of a galaxy

I am aware of upper limits to the mass of burning stars and neutron stars, beyond which they degenerate into neutron stars and black holes respectively. And also, if I understand it right, there is a ...
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48 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 ...
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50 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 ...
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2answers
2k 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 ...
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231 views

How can a black hole zap a galaxy into existence?

I am referring to this picture published here. Apparently super massive black holes emit radiation and matter in astrophysical jets. And these jets can form galaxies. I have some questions: Isn't ...
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339 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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1k views

How much of a galaxy's mass is in stars?

I have been trying to find an answer for this question for a while without a success, so I guess it might not have a specific answer. But to make things easier, let's take the Milky Way galaxy as an ...
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2answers
364 views

Frame dragging — is there a “non-tiny” example?

Now. As I understand it, in fact, the earth (10^25 kg) creates a very small, very tiny, frame dragging effect. Indeed, we have measured this using satellite experiments. So, the Earth (10^25 kg) ...
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1answer
135 views

Dark Matter and Rotational Velocity Curves of Galaxies and Stellar Systems

The way dark matter is introduced to documentary watchers such as myself is to account for the difference between the rotational velocity of the stars in a galaxy compared to that of planets in ...
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1answer
103 views

How can the Andromeda Galaxy alone have more mass than the Local Group?

I was reading about the Local Group, and it is stated that the total mass of the group is $1.29±0.14 × 10^{12}$ Solar masses. The number actually felt a bit low to me because I know the Milky Way ...
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1answer
2k views

Mass/light ratio of galaxies

I'm really stuck. I need to figure out the mass/light ratio of a galaxy in solar units. I know its mass is 5.7 x 1010 solar masses. I know its absolute magnitude (-17.3) and distance (29 Mpc). I'm ...
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301 views

How much gas is in elliptical galaxies?

it is widely known that elliptical galaxies have little or no gas, but how is this determined? What is the amount of gas? Is there a decent ratio of stellar mass to gas for ellipticals? How does ...
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1answer
131 views

Looking for a resource that explains all colors and shapes of stars and galaxies

I've been looking at some of the astronomy pictures of the day from NASA. They all have content that is indicative of certain situations or events. Supernovas have the scattered lines look, new stars ...
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2answers
153 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 ...
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71 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 happens....
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790 views

What is the average mass of galaxies according to Hubble Deep and Ultra Deep field observations?

It is very widely known among people interested in astronomy that there are 100-400 billion stars in the Milky Way galaxy and there are ~ 100 billion galaxies in the observable universe, which is ...
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168 views

Hypervelocity black holes

Is it possible for a black hole to be ejected from a galaxy after an encounter with the central supermassive black hole? What would be the impact of the passage of the hyperV-BH through the galaxy? ...
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106 views

Galaxies Center

It is believed (to my understanding) that at the center of all large galaxies are super massive black holes. Why is it then when you see photos of galaxies that the center is extremely bright if a ...
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1answer
46 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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1answer
62 views

Why are jets not commonly found in spiral galaxies?

Jets and radio lobes are generally associated with elliptical galaxies. Why not spirals?
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32 views

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 ...
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2answers
134 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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1answer
133 views

Could the estimated stellar mass for the Milky Way galaxy include brown dwarfs?

Trying to find an estimate for the stellar mass of the MW galaxy, I found this paper and the estimated stellar mass is $~6.5 \times 10^{10} M_{\odot}$. I was also trying to understand the methods used ...
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55 views

What is the extent of the Galactic Magnetic Field?

What is the extent of the Galactic Magnetic Field? What does the Galactic Magnetic Field look like from afar (such as half-way ...
3
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1answer
242 views

Why do galaxies “disappear?”

So, this bit of information confused me lately. Before, I figured galaxies were no longer visible by us because their luminosity decreased in an inverse square manner. However, while watching a movie ...
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1answer
159 views

What is the space between galactic arms called?

Is there a term referring to space that is inside the plane of a galaxy, but not part of the center/bar/arms/spurs, etc? What's the filler called? The space between two spiral arms (if it isn't a ...
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78 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?
3
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1answer
157 views

Are the cylindrical and spherical form of Jeans' equations equivalent?

The question kind of says it all, what I really want to know is are the differences in their forms only due to the co-ordinate transform? And as such should a suitable spherical system satisfy ...
3
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1answer
177 views

Galaxy Kinematic Fitting: How to deal with Point Spread Function (PSF)

The past few months I have been studying astronomy and Integral Field Spectroscopy (IFS). What I want to do is to fit a galaxy kinematic model to data (ie: estimate the model parameters that give the ...
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2answers
315 views

Rotational velocity of face-on spiral galaxies using spectroscopy

I am doing my first steps in spectroscopy (IFS actually) and how we can learn more about galaxies by using it. I came up with a simple question which, unfortunately, I can not answer: How can we ...
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0answers
66 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 ...
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1answer
58 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? ...
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36 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 ...
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2answers
88 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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0answers
58 views

Dimension of galaxy filaments

Galaxy filaments are amongst the largest known cosmic structures in the universe. They [...] form the boundaries between large voids in the universe. As their name suggests filaments are ...
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1answer
855 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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2answers
60 views

Did physical models of galaxies come before they were actually observed?

Black holes were first predicted by astrophysics, then observed. Was the existence of galaxies first predicted by astrophysics, or first observed by astronomers?
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1answer
385 views

Presence of planets in Milky Way and other galaxies

Are there only planets in the Milky Way galaxy, or are there other planets in other galaxies? If planets are only in the Milky Way, why aren't there planets in others?