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Questions tagged [galactic-dynamics]

Questions regarding interactions between galaxies or between major parts of a galaxy.

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What (actually) is the " deprojected half-light radius" of this almost-all-dark-matter Galaxy?

The recent news of the Ultra Diffuse Galaxy (UDG) Dragonfly 44 is an excellent example of what could be termed 'observe different' thinking. The dragonfly telescope is noted not for the size of its ...
uhoh's user avatar
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7 votes
1 answer
710 views

Is our central black hole actually at the CG of the galaxy?

It seems fairly certain there is a large black hole, about 25,000 ly from Earth roughly in the center of our galaxy, in the direction of the Sag. A radio source. • In fact, is it thought to be ...
Fattie's user avatar
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4 votes
1 answer
270 views

How do two supermassive black holes reach "the last parsec" in the case of merging galaxies?

This answer to Why can't supermassive black holes merge? (or can they?) describes the barrier to merging that two supermassive black holes face when two galaxies are in the process of merging or have "...
uhoh's user avatar
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29 votes
1 answer
3k views

When will the number of stars be a maximum?

There are very roughly a "mole" of stars in the universe. Wikipedia quotes an estimate of $3 \times 10^{23}$ though the number is associated with some debate and uncertainly. I'd like to know if ...
uhoh's user avatar
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12 votes
5 answers
6k views

What mechanism causes oscillations of the solar system's orbit about the galactic plane?

In a recent paper (news release here) Lisa Randall and Matthew Reece propose that a dark matter disk coinciding with the galactic plane together with the solar system's oscillations through the ...
Chris Mueller's user avatar
10 votes
3 answers
2k views

How do we know that supermassive black holes can gain mass by means other than merging with other supermassive black holes?

I just stumbled across the following answer "update" from 2013: This just in, recent observations have ruled out the possibility that SMBHs gain mass only through merging with other black ...
uhoh's user avatar
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8 votes
1 answer
429 views

What is the characteristic time of the evaporation of the galaxies?

For a star, to leave its galaxy, it requires probably a 3-body near-collision at the edge of the galaxy. It is unlikely, but possible. And, if a star once somehow got the required velocity to escape ...
peterh's user avatar
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6 votes
2 answers
789 views

What are the arguments against the Feng and Gallo thin disk explanation of galactic rotation curves?

The well-known galaxy rotation problem is described here. Basically (as one moves outward from the galactic centre, $R$ increasing) the observed pattern of variation in orbital speed $V$ is very ...
steveOw's user avatar
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19 votes
2 answers
2k views

Questions about spiral galaxy arms

I have 2 questions related to spiral galaxies. Firstly, how did the arms form? Why would the stars accumulate into those specific areas? And secondly, why are they still intact? The inner parts of ...
stanley dodds's user avatar
8 votes
1 answer
295 views

Have we discovered a Galaxy lacking in Dark matter?

This question is relevant but it was speaking about a specific discovery reported by pieter van Dokkum, and the answer then mentioned it was disputed whether the paper's conclusion is even correct. I ...
Hisham's user avatar
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5 votes
2 answers
808 views

Why are stars more metallic closer as you move closer to the galactic bulge?

As I see it, most of the stars in the galactic bulge are Population I stars. However, as one moves farther from the galactic bulge, star metallicity decreases. In fact, halo stars are almost entirely ...
Sir Cumference's user avatar
4 votes
2 answers
332 views

Age of the universe

A Galactic year is estimated to be around 250 million "terrestrial" years. That means there will be about 4 rotations per billion years. And age of the universe is estimated to be near 13.8 billion "...
jorel's user avatar
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2 votes
1 answer
8k views

In which direction does the Milky Way rotate?

We don't have a photo of our Milky Way the whole, all the pictures are artists' interpretations showing a bulge, a central bar, and several spiral arms. The milky way is spinning. I would like to know:...
Mishu 米殊's user avatar
2 votes
1 answer
182 views

Can the gravitational potential in a spiral galaxy be positive?

Thinking about this question I wanted to start with a rough model of the average gravitational potential of the Milky way. I ran across D. P. Cox and G. C. Gomez 2002 Analytical Expressions for Spiral ...
uhoh's user avatar
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2 votes
1 answer
967 views

How do galaxies move in space?

Kind of like a shower thought just occurred to me. We've all seen lots of animation about spiral galaxies, how they crash... in virtually all of them, I recall they move in a frisbee way, that is ...
longtry's user avatar
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12 votes
1 answer
452 views

Has the great Andromeda Galaxy ever collided with any galaxies?

We know that the Andromeda Galaxy is moving towards the Milky Way and vice versa, so there will be a collision. Because of the vast space between them, the stars as they are defined will not ...
Isopycnal Oscillation's user avatar
9 votes
3 answers
2k views

Are there some (simple) mathematical models which can simulate the cellular/web structure of the universe?

To visualize the structure of a solar system we have some simple mathematical model: Planets orbiting around a Star in circular motion. If we want to be more precise the circle becomes a ellipse, the ...
J. Doe's user avatar
  • 245
6 votes
0 answers
45 views

Are metallicities of molecular clouds lower in the outskirts of the galaxy?

(this question was originally posted in an answer by user PSR-1937-21 to another post. I find it an interesting one, but since they don't seem to be active anymore, I'm posting it to see if somebody ...
SE - stop firing the good guys's user avatar
5 votes
2 answers
3k views

What is the direction of the movement of the solar system in relation to the galaxy's plane

I got from this answer that the axis of the solar system is tilted of about 63 degrees in relation to that of our galaxy, so I can assume that we move through space (at least locally) roughly in a ...
TomCho's user avatar
  • 390
5 votes
1 answer
162 views

What parameters determine whether galaxies colliding will result in a merger or a hit and run?

Colliding galaxies sometimes merge and sometimes pass through each other. Either way, there are huge changes as a result. What are the parameters that matter in determining whether a collision will ...
Eubie Drew's user avatar
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4 votes
1 answer
448 views

What does "unremarkable transverse peculiar velocity" mean exactly, and how is it calculated here?

The abstract of A magnetar parallax (also in MNRAS) contains the following: Combining our new observations with two archival observations from 2006, we have refined the proper motion and reference ...
uhoh's user avatar
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3 votes
1 answer
184 views

How do disk-shaped galaxies then form at the sites of spherical galactic halos? Do the halo stars start orbiting or just sit in place?

Phys.org's Astronomers detect large amounts of oxygen in ancient star's atmosphere mentions "Stars like J0815+4729 are referred to as halo stars," explained UC San Diego astrophysicist Adam ...
uhoh's user avatar
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3 votes
1 answer
63 views

Can the Hubble expansion inject energy in AGN and quasar outflows?

I found this article about the behavior of quasar outflows in cosmology and how they can create a magnetic field. In section 2.1.4., the authors say that when a quasar produces a "wave" or ...
vengaq's user avatar
  • 937
2 votes
1 answer
397 views

More recent data and simulations of "Milkomeda", the collision of the Milky Way and Andromeda galaxies?

The Space.com headline Hubble Telescope Spots Two Galaxies in a Doomed (but Dazzling) Dance; The galaxies will ultimately crash into each other was probably overstated as seems to be policy in some ...
uhoh's user avatar
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