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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Equation for a galaxy's overall gravitational pull?

Can the Newton's formula be used to express $g$ between two Galaxies in proximity? Gravity on Earth uses two concepts, one is the radius (R) of earth and the other is the distance $h$ from the ...
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149 views

How is the observable universe mapped?

As I was looking at how big earth was relative to everything else in the universe, this picture boggles my mind. http://en.wikipedia.org/wiki/Observable_Universe#Horizons We're like the size of an ...
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245 views

What exactly is expanding when they say universe is expanding? [duplicate]

We know that universe is expanding and galaxies are moving away from each other. Does this mean the galaxies are also expanding in itself and therefore I guess growing larger in volume? Depending on ...
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76 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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2answers
55 views

Why do we have a galactic and a solar plane [duplicate]

Why do all of the planets in our solar system move is (more or less) the same plane? It would seem that the planets should all have very different orbital planes, each at a different angel to each ...
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21 views

Velocity dispersion of galaxies

I couldn't find on web how can I get the velocity dispersion and velocity maps of galaxies from the 3D data cube I get from integral field spectrograph.
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154 views

Galaxies and projected radius vs arcmins

I have two sets of data (globular clusters), one for the Andromeda Galaxy and one for the Milky Way. I want to compare the distribution of globular clusters between the two galaxies according to ...
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38 views

Radiation from farther galaxies

I've read many facts from NASA's webpage.. Sometimes they tell, (for example) "NASA's Chandra X-Ray Observatory discovered this ultra-luminous X-Ray source (about 15 million LY) which shows an ...
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160 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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63 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 ...
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19 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 ...
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16 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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40 views

What's so special about velocity dispersion relations in astrophysics (M-sigma relation, Tully-Fisher, etc)?

I'm confused. Velocity dispersion of stars is measured by Doppler broadening, and through virial theorem that provides information about enclosed masses of galaxy bulges, galaxies, etc, as explained, ...
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32 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 ...
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2answers
48 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 ...
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26 views

Question about Hubble's Law - expansion vs receding velocity [duplicate]

The distance to the galaxy NGC3198 is found to be $15.9 MPc$ and recession velocity is $680km s^{-1}$. What value of Hubble Constant is implied? If $H_0$ is in fact $72 km s^{-1} Mpc^{-1}$, what ...
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76 views

What is the equation for Lin-Shu density wave theory?

Lin-Shu density wave theory is a (very good) theory to explain the spiral arm structure of spiral galaxies. Where can I find the equations that underlie this theory? I've seen its computer ...
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34 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 ...
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142 views

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 ...