Questions tagged [stellar-dynamics]

Questions about the branch of astronomy that studies the regularities in the motions of stars in gravitational fields of stellar systems, as well as the evolution of stellar systems.

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Dynamics of red giant hydrogen shell

From what I understood from this answer to How can a red giant grow so big? But this is not at all the way the shell fusing in a red giant self-regulates its fusion rate-- it cannot regulate its ...
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What does this tweeted Astronomy Plot of the Week mean? What does it represent?

Twitter user BenneHolwerda (@BenneHolwerda) recently tweeted August 10 Astronomy Plot of the Week: And I think @SabineBellstedt and @_jessthorne summary graph deserves a spot for sure. If you work ...
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Is this paper on globular cluster stability still up to date?

I'm looking to better understand the stability of globular clusters for an n-body dynamical simulation, specifically with respect to initial data conditions. I know that the total potential energy ...
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3 votes
2 answers
198 views

How is phase defined in a binary orbit with eccentricity?

Are orbital phases of the black spot in the figure measured from some angle or time/period? Usually, how is phase=0 defined? It is relative to the line of apses perhaps with phase=0 at periastron? Any ...
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Do low-mass red giants last longer than high-mass red giants?

It turns out that red giant stars are not defined by uniform mass. Some can be only one-third as massive as our sun, whereas others can be eight times as massive. So I'm calling the both sides "...
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4 votes
1 answer
91 views

Deriving the first moment of Collisionless Boltzmann Equation in Spherical Polar Coordinates

I am following these notes: Dynamics and Astrophysics of Galaxies. After equation 6.37, we have: \begin{equation*} p_r\,\frac{\partial f}{\partial r} + \frac{p_\theta}{r^2}\,\frac{\partial f}{\...
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  • 471
21 votes
1 answer
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Do the axes of rotation of most stars in the Milky Way align reasonably closely with the axis of galactic rotation?

The axis of rotation of the Solar System makes a large angle of about 60 degrees relative to the axis of rotation of the Milky Way. That seems unusual - for example, most of the bodies within the ...
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Binary star system effects at the barycenter

I haven't been able to find anything on this so far. Using Alpha Centauri as the study, what events/effects ( if any ) would happen between the two stars? More specifically, between the gravitational ...
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Has the plasma amplification of electromagnetic waves in solar type-III bursts (or otherwise in stars) been explored further?

This answer to the SciFi SE question In the novel The Three-Body Problem, does the Sun's amplification of radio transmissions have a scientific basis? cites a 1995 paper published in Chinese Astronomy ...
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1 answer
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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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3 answers
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Can a magnetic field of an object be stronger than its gravity?

Can a planet, star or otherwise have a magnetic field that is stronger or have more range than its gravity?
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Is it possible for stars not to rotate?

I'm just curious about that the existence of non-rotating stars. Is it physically possible for a star not to rotate at all? Does magnetic braking eventually stop the stellar rotation?
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7 votes
1 answer
941 views

What is convection overturn?

When I read some papers about MHD dynamo theory, there is always a $\tau$ that means convection overturning time. What does convection overturn mean?
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1 vote
1 answer
188 views

Is the three-body system "unique"?

Given a state of an ideal 3 body system (i.e., without external interference) in time $t$: the velocity $v_{i,t}$, mass $m_{i,t}$ and position $x_{i,t}$ for $i\in \{1,2,3\}$, using numerical method it ...
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8 votes
2 answers
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Why do stars born in a cluster finally disperse?

In other words, if a group of stars born within the same nebula, e.g. the Pleiades, are initially gravitationally bound - what causes them to finally get separated and proceed individually? Is it the ...
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10 votes
4 answers
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Is any 3 body system known?

https://en.m.wikipedia.org/wiki/Three-body_problem Have three or more celestial bodies rotating each other in a stable manner ever been observed, or it is only a theoretical problem?
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3 votes
2 answers
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List of Moving stars on the northern hemisphere? [Stellar kinematics]

Anyone know if there is a List of Moving stars on the northern Europe hemisphere I can search for? Like Barnard's I wish to image them [when possible] and compare their yearly movement. Thank you
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-1 votes
1 answer
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Star systems forming when large gravitational force is applied

As far as I'm concerned, most star systems in our galaxy are traveling in fairly circular paths around the black hole at the center. Hypothetically, if a large gravitational force pulled star ...
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1 vote
1 answer
68 views

how far away can close stars diverge with time?

Do high velocity stars decelerate if they transit at 300ly per million years? What kind of forces can decelerate them and in what kind of time frame? What about ordinary stars which travel at 70 ...
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6 votes
3 answers
2k views

Are the stars outside of the galactic plane in the galactic halo?

The majority of the stars we see in the sky, like Pollux, are outside of the galactic plane. That means that all those stars we see are not in the galactic disk, and therefore are in the galactic halo,...
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2 votes
1 answer
125 views

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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1 vote
1 answer
141 views

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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2 votes
1 answer
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Why aren't stars like Eternally Collapsing Objects?

We know that stellar radiation pressure balances the gravitational compressive forced of a star. Are there other factors which resist such a collapse? Also, if radiation pressure balances ...
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1 vote
0 answers
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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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5 votes
1 answer
3k views

Why is the Sun's brightness and radius increasing, but not its temperature?

On the Sun's article on Wikipedia, there is an image showing how the Sun's brightness, radius and temperature have changed over time: For the past (and next) few billion years, I see the luminosity ...
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6 votes
3 answers
693 views

If a white dwarf collides with a giant star, could it create a TZO?

Thorne–Żytkow objects (TZOs) form from collisions between neutron stars and main sequence or giant stars. Ultimately, the neutron star becomes the "core" of the giant star. However, could this also ...
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4 votes
1 answer
570 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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5 votes
1 answer
7k views

How do star densities work?

If we take a look at stars more massive than the Sun, their densities vary a lot. UY Scuti is an extremely low-density star that's only 8.5x more massive than the Sun, but is 1000-2000x its size. ...
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4 votes
1 answer
2k views

Does the Sun orbit the Milky way in a (kind of) flat or inclined orbit or more of a sine wave? [duplicate]

I know it can't be a perfect ellipse or smooth orbit due to all the matter in every direction, and our Sun could be affected by a gravity assist of sorts if it passes close enough to another massive ...
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1 vote
1 answer
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Realistic space environments [closed]

You've seen it in all kinds of science fiction, be it books, games, movies, and such. Space is depicted all sorts of ways, with asteroids far too close together, nebula thick enough to hide in and ...
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4 votes
1 answer
94 views

Reference for equation of state?

I am a post graduate studying mathematics and currently working on the mathematical theory of stars though not an expert. When I am making some assumption about the equation of state (for a star or ...
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2 votes
1 answer
113 views

Trouble understanding speed-dispersion in (elliptical) galaxies

I'm learning about LOSVDs (Line Of Sight Velocity Distributions) and I'm having a bit of trouble understanding the used terms. As I understand, the LOSVD of a given (elliptical) galaxy is the density ...
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2 votes
1 answer
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Milky Way stellar number density : is the stated equation in this paper incorrect?

The paper is : http://www.astro.washington.edu/users/ivezic/Publications/tomographyI.pdf The equation is equation #23 in the paper. It's a model for the density of stars in the Milky Way's disk. It ...
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4 votes
3 answers
547 views

Pulsation Modes of Cepheids

There are various modes of Cepheids like single modes: fundamental (F), first overtone (1O), and likewise. And then we have double modes: F/1O, 1O/2O etc. triple modes: 1O/2O/3O etc. What ...
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4 votes
2 answers
963 views

Hamiltonian of general three body problem

i try to extend my analysis from planar restricted three body problem to the general one. Is there anyone that can help me to find out the Hamiltonian for this prolem in cartesian coordinates? I ...
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9 votes
1 answer
132 views

How can the life time of a multiple star system, such as for example the trinary system PSR J0337+1715 be derived?

As for example explained at the beginning of this blog post, the trinary system consists of a millisecond pulsar ($1.438$ times the mass of the sun) orbited by two white dwarfs. One of the white ...
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8 votes
2 answers
237 views

On analogies between gas and stellar systems

Analogies between (typically) ideal gas and stellar systems are not only intuitively valid to some extent, but have been established and used in the studies of stellar clusters and galactic systems, ...
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16 votes
2 answers
207 views

Relativistic effects in stellar dynamical systems

I am curious, if anybody knows of any stellar dynamical systems/environments, where relativistic effects could play a dynamical role on the motion of these stellar systems? As a subquestion - are ...
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