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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179 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 ...
3
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1answer
103 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 ...
5
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1answer
96 views

According to the initial mass function, should there be more brown dwarfs than red dwarfs?

According to the IMF and the stellar mass distribution, stars become more abundant the less massive they are. And while objects must have a mass > 0.075 solar mass to become a star, brown dwarfs with ...
4
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1answer
312 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 ...
3
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2answers
294 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 ...
6
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2answers
1k views

What is the luminosity of the Milky Way galaxy?

The luminosity of the Milky Way galaxy according to this is $5\times10^{36}$ Watts, but this number suggests that there are about 10 billion stars with Solar luminosities in the Milky Way, which ...
3
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1answer
76 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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2answers
2k 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 ...
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3answers
2k views

Why don't stars have Keplerian orbits?

In a comment to Rob Jeffries' answer to this question on spherical galaxies, Incnis Mrsi commented There should exist the entire range of orbits in a spherically symmetric system: near-circular, ...
35
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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 ...
11
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1answer
198 views

Are the orientations of spin-axes and binary/planetary orbits random or is there any relationship with the Galactic plane?

In an answer to another question, a claim has been made that orbit/spin orientations are random (at least within our own Galaxy), except perhaps towards the Galactic centre. I have dabbled in 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?
6
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2answers
214 views

How can we differentiate between matter and antimatter? [duplicate]

For instance if there was a galaxy, assume it to be made up of antimatter (isolated from other "normal" galaxies), how would we, or rather, would we be able to distinguish if it was made up of matter ...
9
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1answer
451 views

Are the distances we measure to objects in the universe incorrect because of their relative motion?

For example the agreed distance to the Andromeda Galaxy is 2.5 million light years, and consequentially, we see the galaxy as it was 2.5 million years ago! (A time interval in which the galaxy must ...
6
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3answers
2k views

How many more galaxies are out there in the Universe (beyond the observable radius)?

Let's say that the number of large galaxies in the observable universe is $n$ (approximated to 350 billion). If the universe is homogenous and isotropic, what are the estimations for the total number ...
0
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1answer
31 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 ...
0
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1answer
99 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 ...
0
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0answers
98 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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0answers
125 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 ...
9
votes
1answer
136 views

Is it possible to determine whether distant galaxies are gravitationally bound

In a previous question, one issue was related to the potential energy of cosmic structures. This raised in particular the question of whether these structures are gravitationally bound. If you ...
2
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1answer
87 views

Measuring more accurately the distance of remote galaxies

From what I read in Wikipedia, the velocity of a Galaxy has two components: one is due to Hubble's law for cosmic expansion, and the other is the peculiar velocity of the galaxy. Since the peculiar ...
0
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1answer
26 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 ...
2
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1answer
277 views

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?
4
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1answer
187 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 ...
2
votes
1answer
64 views

How is dark matter meant to explain the faster than expected rotation of galaxies? [duplicate]

The stars on the outer edges of galaxies go around faster than they should be. How is dark matter meant to account for this? if you just add more mass wont that just give it a greater gravitational ...
2
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1answer
365 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?
5
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4answers
93 views

Why doesn't the light from galaxies appear stretched? [duplicate]

Maybe it's my ignorance of astrophysics/cosmology, but I have been wondering this: Why do galaxies not appear stretched when we observe them? Assuming a galaxy that we observe is 100,000 light years ...
0
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0answers
34 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 ...
3
votes
1answer
86 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
votes
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)
2
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1answer
88 views

Adding matter to make galaxies bigger

What are the actual factors that play a role in the accretion of matter into galaxies? I read about Accretion Disks but I don't quite understand how they work yet.
12
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1answer
2k views

Why don't the black holes appear black in color in images of galaxies taken from HST?

According to NASA a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area According to the documentary Space Unraveling The Cosmos about ...
3
votes
2answers
244 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) ...
2
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1answer
66 views

Distance from redshift

I am looking for a exact derivation of a relation between redshift $z$ and distance $d$. What I know is the definition ...
1
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1answer
61 views

Are galaxies “disk” shaped?

When you look a sphere from a fixed observation point, you can easily mistake it for a circle, so I was wondering: are galaxies really "disk" shaped or we just don't have the means to detect the ...
0
votes
2answers
80 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 ...
1
vote
2answers
132 views

Redshift 1+z - CMB Temperature lower?

I know that $\frac{\lambda_2}{\lambda_1} = 1 + z$ Suppose a galaxy had redshfit $z=3$. Does this mean that the wavelength becomes $4\lambda$? Then by wien's law where $\lambda \propto \frac{1}{T}$, ...
2
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1answer
66 views

Current map of galaxies' z's and distances?

So, here's a diagram with some galaxies. I realize there are 500 billion galaxies out there (likely many more), but is there are fairly up-to-date diagram of all the galaxies, or a representative ...
2
votes
1answer
105 views

Approaching of Milky way to M87

The Andromeda Galaxy is approaching the Milky Way at about 110 kilometres per second (68 mi/s). What is the velocity that Milky way is approaching M87 ?
2
votes
2answers
120 views

Lagrangian point or dark matter?

We know that spiral galaxies spin in a way such that we have to assume that dark matter is responsible for the extra mass required to do so. My question is, can Lagrangian points (L1 and L2) be used ...
2
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0answers
50 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 ...
3
votes
1answer
43 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 ...
4
votes
1answer
180 views

Correlation between large-scale galaxy structure and CMB fluctuations?

During a relatively non-technical astronomy seminar the other day, the speaker displayed the famous WMAP full-sky image as an aid to describing what the CMB is, the scale of its fluctuations, etc. ...
8
votes
4answers
2k views

How Are Galaxies Receding Faster Than Light Visible To Observers?

We know that some galaxies are moving away from us faster than the speed of light and we know it by measuring the redshift, but how's that possible? If they're moving away say at 2c, how would the ...
2
votes
1answer
59 views

Does the rate of expansion of the universe exceed the rate at which the local group is being pulled toward the Great Attractor?

I understand that the expansion rate of the universe driven dark energy exceeds the rate at which the local group is being pulled toward The Great Attractor (Hydra-Centaurus Supercluster). Does this ...
1
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2answers
56 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 ...
1
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0answers
28 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.
3
votes
1answer
220 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 ...
2
votes
1answer
235 views

why galaxies look like discs rather than spheres? [duplicate]

Black holes have much gravitation to hold all stars and nebulas but why they are aligned in disc type shapes rather than spheres because gravitation is everywhere around black holes. Even on upper ...
6
votes
1answer
98 views

How are stellar and galactic ages determined?

Being a 4th year undergraduate physicist, you'd think I'd know this! But it's never really taught in any detail, just vague mentions of metallicities and, in galactic case, redshift. So how exactly ...