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.
4
votes
1answer
214 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 ...
4
votes
0answers
94 views
Relation between isophotal radius and virial radius in spiral galaxies?
Is there any (proposed) relation between the B-band isophotal radius of a spiral galaxy and its virial radius (r_200)?
If you know of such a relation, please post a reference paper.
3
votes
1answer
85 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 ...
3
votes
3answers
177 views
How do we know for certain that space is expanding?
How do we know for certain that space is expanding?
Let's say that in the year 1950, we observe that galaxy 1 is 5 billion light years away from us and galaxy 2 is 10 billion light years away from ...
3
votes
3answers
43 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?
3
votes
3answers
61 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?
3
votes
1answer
108 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 ...
3
votes
1answer
31 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 ...
3
votes
1answer
25 views
Why are jets not commonly found in spiral galaxies?
Jets and radio lobes are generally associated with elliptical galaxies. Why not spirals?
3
votes
1answer
26 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 ...
3
votes
1answer
173 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 ...
2
votes
5answers
785 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 ...
2
votes
3answers
81 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
votes
1answer
13 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?
2
votes
1answer
148 views
If we were to travel through space (sci-fi style), how close to the false-color images would the galaxies we see be?
I understand that the black-and-white images you see looking through a household telescope are only like that due to the intensity of the light that reaches us, and that most of the astronomy images ...
2
votes
2answers
254 views
At what distance could you see andromeda with the naked eye?
We've all seen the telescope photographs of andromeda galaxy:
I'm wondering if it were possible to travel close enough to the andromeda galaxy could you achieve a same perspective with the naked ...
2
votes
1answer
88 views
When would the proposed black hole at the centre of Milky Way gulp in our solar system?
I've heard and read that our solar system lies near to the peripheral region of the Galaxy. Then accordingly we would have a greater probability of sustaining to eventual gulping down by the ...
2
votes
3answers
204 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 ...
2
votes
2answers
507 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 ...
2
votes
1answer
37 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 ...
2
votes
1answer
415 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 ...
2
votes
2answers
158 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 ...
2
votes
2answers
87 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 ...
2
votes
1answer
27 views
How do we explain the phase change between high and low star formation rates?
During a recent talk I was at, someone, who models galaxy characteristics from dust amounts and spectral energy distributions (SEDs), quoted a fairly prompt change from 'high' to 'low' stellar ...
2
votes
1answer
57 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 ...
2
votes
1answer
48 views
Creating/Downloading a large Galaxy Dataset
I was wondering where I can get a more or less complete set of a galaxy to test an n-body simulation (preferably two colliding galaxies with approx 300k to 1M elements).
Is it possible to extract ...
2
votes
1answer
345 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 ...
1
vote
1answer
66 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 ...
1
vote
1answer
74 views
Why are galactic centers always brighter than the edges?
As you can see this image http://i.stack.imgur.com/YOt8C.jpg and other galaxy images, the centers generally much brighter.
Why is that?
Is there a very big star? A very big gravitational field?
1
vote
3answers
15 views
Is there a correlation between the mass of a supermassive black hole and the mass of its host galaxy?
I would love to know! I can find lots about the mass-velocity dispersion relation. There's a mass-luminosity relation (but not really tight). I hope you can include references, as I'm spending ...
1
vote
2answers
69 views
What is the Schechter luminosity function's domain of support?
I'm trying to fit a Schechter luminosity function to some data points, but it's not clear from this definition what the domain of support of the PDF should be. I'm familiar with the standard Pareto ...
1
vote
1answer
322 views
Does the large red shift value of galaxies mean they are far away?
When the red shifts of galaxies are large, why do we think that they are far away?
I know about Hubble's law, Tully-Fisher relation of spiral galaxies, Faber-Jackson relation of elliptical ...
1
vote
1answer
80 views
Gravitation within galaxies
Do all galaxies radiate gravitational waves? What is the origin of these waves, the origin of the Galactic center? If it exists, do two galaxies warp together due to these waves, when they come ...
1
vote
1answer
192 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
1
vote
0answers
78 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 ...
1
vote
0answers
176 views
Why do galaxies collide? Reconciling dark energy and an expanding universe with the fact that some galaxies are on a collision course
My layman understanding of cosmology is:
galaxies are uniformly (more or less) spread throughout the universe, per the Big Bang and the fact that in a central explosion, all dispersed points are ...
0
votes
1answer
35 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 ...
0
votes
2answers
404 views
how can galaxies collide if everything moving outwards
If the universe started from Big Bang and everything is expanding outwards and actually accelerating away from each other, than "How is it possible for two galaxies to collide as they all are moving ...
0
votes
1answer
132 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 ...
0
votes
0answers
70 views
Doubts about NASA's announcement of collision between Milky Way and Andromeda [closed]
Andromeda is one of the nearest big gallaxies out there.
We can estimate the distance to the Andromeda Galaxy measuring the apparent brightness of Cepheid variable stars; its distance is currently ...
0
votes
0answers
46 views
Flung out of the galaxy
I watched a video by Dr. Michio Kaku, in which he states a theory about Dark Matter.
This theory says that Dark Matter could be just ordinary matter from another parallel universe, which would be ...
0
votes
0answers
31 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 ...
0
votes
0answers
37 views
Far stellar object going away from us faster than light [duplicate]
Possible Duplicate:
What does Brian Greene mean when he claims we wont be able to observe light from distant stars due to the universe’s expansion?
Since the galaxies are fleeing us faster ...
