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Questions tagged [galactic-dynamics]

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

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Galactic rotation speeds - questions from a non-astronomer

Are there any observations that more distant galaxies appear to rotate more slowly than closer galaxies? What methods are used to measure the rotational speed of galaxies? (both orbital speed ...
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Population histograms and relationship between size of galactic disk and amount of dark matter

I am interested in seeing a plot of dark to baryonic matter ratios in terms of the galactic disk size (when it applies, as not all galaxies fit into disk shapes, and probably analyzing disk galaxies ...
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1answer
116 views

Is it possible to define a state of zero absolute angular momentum anywhere in the universe?

Conservation of angular momentum doesn't seem correct to me. I think this because radiation is present everywhere, no space is completely void, and no object perfect. Thus all objects will have uneven ...
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Looking for a Dwarf Galaxy < 500 L.y. in Diameter, which is not a Satellite / Companion, or is at least 500 000 L.y. away from another Galaxy

My goal is to learn about an example of a Dwarf Spheroidal or a Dwarf Irregular Galaxy which is not a Satellite / Companion Galaxy (or is at least 500 000 L.y. away from another Galaxy), and doesn't ...
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1answer
105 views

Direction of Earth’s poles relative to the Sun’s movement around the Galaxy

The plane of the solar system is at 63 degrees to the plane of the galaxy, then either the North or South Pole of Earth would be on the ‘leading edge,’ i.e. pointing roughly in the direction of ...
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Is the Milky Way Galaxy predicted to collide with a neighboring galaxy? [duplicate]

Topic I've read several articles online that state that our galaxy will collide with a neighboring galaxy in the future, but there is no evidence about it happening. Question(s) After reading a ...
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1answer
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Is diffuse energy distribution considered in the galaxy rotation curve explanations?

Problem number 23 in chapter 1 of Purcell's "Electricity and Magnetism" Second edition page 37 shows that 90% of the energy stored in the electrostatic field of a spherical charge distribution of ...
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57 views

Is the expected time for a star in an elliptical galaxy to collide with another star less than the average age of elliptical galaxies?

According to the Wikipedia article Elliptical galaxy, elliptical galaxies have a much lower concentration of gas between the stars than spiral galaxies. I know that until the gas is below a certain ...
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Half of the Milky Way's baryonic mass is from other galaxies - when did this happen?

The recent Phys.org article Milky Way's origins are not what they seem explains the recent MNRAS article Anglés-Alcázar et al. 2017; The cosmic baryon cycle and galaxy mass assembly in the FIRE ...
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1answer
1k 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:...
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2answers
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Does the Abell 1689 supercluster have angular momentum?

The Abell 1689 is a large group of galaxies, containing a lot of elliptical galaxies : https://en.wikipedia.org/wiki/Abell_1689 Usually, an elliptical galaxy don't have large angular momentum around ...
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Need help on Springel model for galaxy simulation

I am working on a code for galactic dynamics simulation. Initial conditions (positions and velocities) are based on a model with a massive dark halo and a thin exponential disk. Now, from the ...
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1answer
352 views

Star density in- versus out- of the arms of the galactic pattern?

What is the density difference in our galaxy (or in a typical spiral), at A, B, C versus at a, b, c? Consider the yellow track. Do astronomers have a graph like this... ...which shows the shape of ...
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1answer
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Why does the neutral hydrogen velocity have this characteristic behavior in the galactic plane?

The recently released map of galactic neutral hydrogen density and velocity is really beautiful. The work has been relased by the HI4PI collaboration (HI = neutral hydrogen, $4\pi$ = complete ...
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1answer
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Examples of astrophysical objects NOT in virial equilibrium?

Astronomers always talk about astrophysical objects being in virial equilibrium (e.g., a stellar system, or a disk of gas within a galaxy, etc.). But I never hear about thermodynamical equilibrium. ...
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Ellipticals supported by random motions

As opposed to spiral galaxies, which are rotationally supported, elliptical galaxies are said to be supported by random motions of their stars. I don't really have an intuitive understanding of this. ...
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760 views

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 ...
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1answer
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Is a swimming pool analogy to building of black holes in the centers of galaxies valid?

In our garden, we have a little pool to enjoy our 2 children. It is 3 meters in diameter and contains some 4 m³ of water. For cleaning-convenience every evening I go walking some 5 or 10 rounds in ...
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1answer
146 views

Why don't globular clusters flatten with a galactic disc?

Globular clusters lie in the galactic halo, outside of the disc. However, galaxies are more or less a collection of material and objects — why is it, then, that most stars form a plane due to the ...
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Virial coefficient when computing dynamical mass enclosed by a rotating galactic disk of gas

Suppose I have a large thin disk of rotating gas in a galaxy -- the disk has a maximum inclination-corrected $V_{max}$ and a maximum radial extent of $R_{max}$ corresponding to that $V_{max}$ ...
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1answer
274 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 ...
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1answer
251 views

Stellar systems: what is the difference between virial, dynamical and thermodynamic equilibrium?

I'm currently going through Binney & Tremaine (2008) on my own to learn about stellar dynamics. I also have been perusing additional online resources such as this scholarpedia wiki. Often when ...
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Why Milky Way and Andromeda are being drawn together if there was 'Big Bang'?

Scientists used to use following reasoning: most galaxies are red-shifted $\implies$ there was a 'Big Bang' Why this is being considered valid since not every galaxy has such property?
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Is the motion of the Sun around the Galaxy a result of gravitational pull?

Does the orbit of the sun (and other stars within the Milky way) around the galaxy result directly from radial gravitational force toward the objects in the center of the galaxy, or is there ...
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2answers
426 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 ...
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1answer
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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 ...
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1answer
199 views

Distribution of Stars in Milky Way and globular cluster analogy

Just a quick (and hopefully simple) question on the distribution of stars in the Milky Way and in globular clusters. I was wondering why it IS NOT possible to describe the distributions of stars in ...
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2answers
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Is the Astronomy community still concerned about the lumpyness of matter distribution in the universe?

A decade or so ago, when I was still a science undergrad, one of the open questions in astrophysics was to explain the uneven distribution of galaxies in the observable universe. That is, why did the ...
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1answer
268 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 ...
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3answers
497 views

What happens to galaxies when they die?

Stars explode when they die and blast heavy elements into space. Do galaxies do the same thing?
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2answers
1k views

Leaving the Milky Way

If we had a hypothetical spacecraft, would it be possible to exit our galaxy, wait for some time and enter back into another section? Will this method be more efficient that a more traditional flight ...
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2answers
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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 ...
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1answer
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What will the mass of the new galaxy be?

When the Milky Way galaxy collides with the Andromeda galaxy, what will the mass and volume of the new galaxy be?
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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 ...
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1answer
62 views

Exploiting symmetry in the axisymmetric Jeans equations

I'm solving the axisymmetric Jeans equations to determine the initial conditions for an exponential disk inside an NFW halo. The density profiles of the two components are \begin{equation} \rho_d(R,z)...
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1answer
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Could discoid galaxies be expanding?

I understand that astronomers once thought that the material in the disc of a galaxy was moving around the galactic centre (where most of the mass was thought to be) in roughly circular orbits. The ...
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1answer
366 views

Python 2D Jean Instability in Spiral Galaxy Simulation

I have ~1000 snapshots of a spiral galaxy simulation (from Molecular cloud perturbations t=0 to t>1Gyr. What I need to do is determine whether any position at any of the snapshot times meets criteria ...
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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 ...
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2answers
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Are there a lot of collisions between stars in the core of the galaxy?

I'm reading on Wikipedia about Halo Stars that orbit the center of the galaxy at a high inclination away from the plane of the Milky Way. It seems that at some point, these stars must dive back into ...
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1answer
421 views

Could dark energy be negative gravity?

Main question: Could dark energy (the mysterious accelerating expansion of the universe) be explained by "negative gravity"? "Spin off" questions: Does antimatter have negative gravity? If ...
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1answer
537 views

What is $v_{GSR}$

In this paper ("The Apache Point Observatory Galactic Evolution Experiment: First Detection of High Velocity Milky Way Bar Stars") they plot and calculate $v_{GSR}$. $GSR$ stands for Galactic Standard ...
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1answer
254 views

Dark Flow: statistical limits on existence

Dark Flow has been thrown around as a term a lot lately, especially with the latest Planck results. New Scientist reported last year that it was now statistically improbable, but the paper by Atrio ...
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76 views

Will we ever end up in the black hole? [duplicate]

Since we are spiraling around the black whole will we spiral into the black hole?
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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 ...
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2answers
223 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 "...
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1answer
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Do we live in a galactic bubble?

I have heard a certain statement, which can be summarized succinctly into "we live in a local bubble", implying that solar system is located in an intestrellar dust underdensity region. This region ...
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Two species of dark matter?

At this point in time, evidence for the existence of dark matter has accumulated in many ways: it affects galactic rotation curves plays a major role in cosmology, and the evolution of structure in ...