Questions tagged [galactic-dynamics]

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

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Do the stars in irregular galaxies orbit anything?

Do the stars of irregular galaxies (such as the Magellanic clouds) orbit a more precise point or are they just, I don't know, flying around? If they orbit, how stable would such orbits be, considering ...
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Will the Sagittarius A* Black Hole eventually swallow the entire Galaxy?

In one of his interviews, Sir Roger Penrose mentioned that when the Milky Way and the Andromeda galaxies eventually "collide" and merge into one, their super-massive black holes will also ...
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Does this black hole mass/galaxy stellar mass relation hold for extremely low-mass galaxies?

I read a preprint last week (Palmese & Conselice 2020) that suggested that the recent gravitational wave detection GW190521 could be the end result of a merger of two extremely low-mass galaxies. ...
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Figure out the location of celestial objects relative to the Milky Way in x, y, z co-ordinates

I am trying to place various celestial objects the correct distance from the Milky Way, using x, y, z co-ordinates. So assuming the centre-of-mass of the Milky Way is at 0, 0, 0 - how can I figure out ...
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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 ...
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Strip Brightness in a Spherical System

My question concerns the following problem, published in Galactic Dynamics by Binney and Tremaine and based on a work by Schwarzschild. Specifically, I am having difficulties in deriving the given ...
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Why is SPT0418-47 (“the most distant Milky Way look-alike”) expected to evolve into an elliptical galaxy?

Phys.org's ALMA sees most distant Milky Way look-alike describes the image reconstruction of a strongly and very nicely lensed z = 4.2 galaxy by a by a foreground galaxy at z = 0.263 and says: "...
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How do they know the newly-spotted gas near the center of our galaxy is molecular without knowing what gas it is?

Phys.org's Mystery gas discovered near center of Milky Way links to Teodoro et al 2020 in Nature Cold gas in the Milky Way’s nuclear wind who's abstract is shown below. Question: My reading of the ...
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Do the orbits of satellite galaxies show the influence of dark matter?

I understand how galaxy rotation curves show the influence of dark matter, or something else that would produce similar behaviour, such as Modified Newtonian Dynamics (MOND). Do the orbits of ...
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54 views

What does correcting for LSR mean in galactic velocities?

This is a two-part question, but both parts are related: I'm aware that modern astronomical software can correct velocities for the local standard of rest (LSR), but what does that really mean? As in,...
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What's so interesting about Coma-type galaxy clusters?

When the dynamical mass of a proto-cluster of galaxies is ~(1-2)x1014 Msolar, the proto-cluster is expected to evolve into a coma-type cluster. In almost every paper I read about the confirmation of ...
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Orphaned star systems and intergalactic travel (in fictional context)

Context: I'm looking for some authority on a particular idea that I brought up in regards to a new update brought out for a space travel sim game, Elite Dangerous The vessels in that game can travel ...
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What are Stokes parameters for galaxy shapes, how do they compare to Stokes parameters in optics?

I remember Stokes parameters as a way to completely define the polarization state of a well-defined beam of light. However several questions here refer to Stokes parameters used in characterizing the ...
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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 ...
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How is the Sun tilted to its orbit around the Milky Way's center?

We know how the Sun is tilted in reference to its planets but how is it tilted to Sagittarius A or its orbit around it? Or isn't it tilted at all?
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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 ...
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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 ...
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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 ...
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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 ...
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Galaxy interactions

What causes galaxies to merge, rather than orbit indefinitely?
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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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What is the largest cluster of merging galaxies?

Reading about the Andromeda–Milky Way collision, a galactic collision predicted to occur in about 4.5 billion years between the two galaxies, I went to the galaxy merger page and Wikipedia states that ...
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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 ...
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Supergalactic and Equatorial coordinates

What's the difference between Supergalactic and Equatorial coordinates?
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How do two supermassive black holes reach “the last parsec” in 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 "...
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Dynamical modelling of galaxies with counter-rotating components using the Schwarzschild method

I am currently trying to understand dynamical modelling using Schwarzschild's method. I have been doing some reading the past days, but I suspect that I am getting something really wrong. According to ...
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What has GAIA found out about the dwarf galaxy heritage of stars in the Milky Way, if anything?

I ran across the image below in the August 2000 ESA Bulletin # 103 GAIA – Unravelling the Origin and Evolution of Our Galaxy Figure 3. This simulation shows how a galaxy halo, like our own, may ...
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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 ...
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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 ...
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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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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 ...