Questions tagged [galaxy-rotation-curve]

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Galaxy rotation curve and galaxy mass

Is there a relation between the saturation velocity of the galaxy rotation curve and the luminous mass of the galaxy? To clarify the question, if one were to plot a scatter plot with the x-axis as the ...
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4 answers
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Why would GR's prediction for galaxy rotation curves differ from Newtonian gravity's in spite of prevailing intuition from dimensional analysis?

Until recently, I had assumed that the predicted (non-dark matter) galaxy rotation curves shown in plots such the one on the Wikipedia article were calculated with general relativity. However, I now ...
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2 answers
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Does loop quantum gravity explain the dark matter effect without dark matter?

Does loop quantum gravity explain the dark matter effect (the rotational curves of the galaxies, the increased velocitoes of galaxies within galaxy clusters) without using dark matter? As far as I ...
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2 answers
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Thought experiment on boundary condition of galaxies

A thought experiment: Let's assume that there is only one single galaxy in the whole universe. How would it look like regarding the curvature of spacetime? Would the spacetime be flat in the infinity ...
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2 answers
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Asymptotical flatness for galaxies - Why?

During the construction of solutions for General Relativity (when leaving out Lambda), asymptotical flatness is always assumed. Why? I fully understand that it fits the solar system, as it results in ...
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1 answer
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Why do we need hot dark matter?

Data on galaxy rotation curves suggested that not all the mass in the galaxy is accounted for and we can't observe them directly but remind me again why we need hot dark matter in the first place? ...
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1 answer
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Do counter rotating galaxies have dark matter?

Have counter rotating dark matter galaxies been observed? Counter rotating galaxies, you may already know, are galaxies where some stars or arms rotate in one direction and other stars or arms rotate ...
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0 answers
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What is the effect of a supermassive black hole at the centre of the galaxy on this galaxy's spectrum?

After analysing the spectrum of the spiral galaxy (featuring flat rotation curve) we are asked to draw a sketch showing the effect on the galaxy spectrum if the galaxy were to have a supermassive ...
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4 votes
1 answer
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Boundary condition for gravity on galaxy scale?

In general relativity, on the one hand, asymptotical flatness is assumed to derive a solution to the EFE which is a good approximation in the solar system (Schwarzschild, Kerr...) On the other hand, ...
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1 answer
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At the other edge beyond Newton with General Relativity? #2

The Schwarzschild solution is derived by using the static, spherically symmetric solution $$ds^2=-B(r)dt^2 + A(r) dr^2 +\text{angular terms},$$ assuming a concentrated mass, therefore gaining $A=1/B$ ...
14 votes
3 answers
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Is Dark Matter in Motion?

What is known about the motion of dark matter, especially in galaxies? It seems as though a particular distribution of dark matter might be required to cause the very flat galactic rotation curves ...
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1 answer
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Derivation of gravitational potential for Einasto model

I'm following this paper to understand how the gravitational potential is derived for the Einasto model: https://www.aanda.org/articles/aa/full_html/2012/04/aa18543-11/aa18543-11.html. I got stuck ...
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Why does $10^{-31}$K change the orbits of the stars, but 2.7K does not?

Many people discussing the rotation curves of the stars in galaxies explain that the rotation curves are influenced by a cosmological acceleration of about $1.2 \cdot 10^{-10}\,\rm m/s^2$, and that ...
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4 votes
2 answers
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Can Vera Rubin's findings be explained by a distribution of charge?

Vera Rubin found that the rotational velocity of galaxies is much greater than expected at greater distances from the center. Gravity from an invisible mass is assumed to account for this measurement. ...
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2 votes
0 answers
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Does barred in spirals galaxies like ours have the same speed (spin) as the center black hole?

In the case of old galaxies (elliptical) the black hole, like one in M87 have 2 jets. This look like polarisation pushing from central BH. In barred spiral galaxies, the bar have to cross the central ...
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Rotation of galaxies and gravitomagnetism [duplicate]

Can we explain the bigger speed of rotation of the galaxies from gravitomagnetic field acting from the "inner layers" of the galaxy to the "outer layers" of the galaxy?
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1 answer
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Is it true that frame-dragging (as applied to galactic rotation curves) goes as second order in $v/c$ rather than $(GM/Rc²)(v/R)$?

I have seen various people (see e.g. comments here) dismissing this article using the argument that GR frame-dragging is second order in $v/c$ and therefore insignificant because $v << c$ for ...
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1 answer
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Galactic rotation curves question

I think I need to ask this question now, because it's in my mind for several years and I just can't find an answer to it. After observations of those galaxtic rotation curves, it's pretty clear, that ...
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2 answers
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Forces besides gravity acting at astronomical distances?

It seems like all one reads about is gravity affecting planets and stars whereas at the atomic level there are other forces and gravity is unimportant. How do we know there are not other forces ...
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5 votes
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Fully General Relativistic treatment of Galaxy Rotation Curve

Over the years I have seen several approaches to this problem in the GR context: perturbations around a flat-spacetime, cancelation by hand of $\mathcal{O}(\partial_{\mu}\textbf{g}^{2})$ terms on the ...
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1 answer
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Is there software to calculate/plot decomposed rotation curves from observational data (FITS, etc)?

I have observation data of galaxies (in FITS format). From the FITS data, I want to calculate & plot the decomposed rotation curves as pictured below. Is there a software package that will do that ...
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2 answers
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How much faster are the stars on the outskirts of galaxies going than they are 'meant' to as predicted by general relativity?

this is in reference to dark matter. I've look on the internet for this but I can't find precisely what I am looking for.
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Unruh effect on rotating galaxies?

According to the Unruh effect, an accelerating observer will experience a thermal bath. This is equivalent to Hawking radiation. If we applied this to a spinning galaxy, I wonder if this thermal bath ...
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2 answers
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How can I plot Rotation Curves of Spiral Galaxies $v$ (km/s) vs $r$ (kly)?

I have a formula about Rotation Curves of Spiral Galaxies that I have written below: $$v(r)=c [L/(2*r)+1/2\cdot c_3+ c_4\cdot\ln(r)]^{1/2}$$ that $c=3\cdot10^8m/s$ is the speed of light and $c_3=2.8\...
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Are there galaxies with satellites in retrograde orbit?

If frame dragging is important for properly calculating galactic rotation curves, it seems that galactic satellites in retrograde orbit should behave as if they experience a different amount of ...
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7 votes
2 answers
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Has frame dragging been accounted for in galactic rotation curves?

This article explicitly takes frame dragging into account in calculating expected galactic rotation curves in the absence of dark matter, and appears to obtain very close matches to observed curves. ...
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2 votes
1 answer
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Is galactic gravitational lensing self-magnification big enough to contribute noticeably to the galaxy rotation curve problem?

Gravitational lenses magnifies the appearance of themselves, so in the case of a galaxy it looks bigger than it is. Thus the outer stars in a galaxy seems to have a higher tangential velocity. For ...
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1 answer
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How could I calculate the circumferential velocity of stars in an idealized spherical galaxy from the distribution of mass through that galaxy? [closed]

We will assume that the galaxy is a sphere where stars orbit around the center on different radii. Since there are so many stars, we will not deal with individual stars, but we will assume that the ...
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Does dark matter interact with baryonic matter only through the gravitational field? [duplicate]

Do I understand correctly that dark matter fields are interact with baryonic matter only through the gravitational field? In this case, how can it be registred at all if it does not interact with the ...
1 vote
5 answers
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Are orbiting masses in a uniform disc affected by masses outside its orbit?

For a sphere of uniform density, we know an orbiting mass experiences a net attraction only by the mass inside its orbit, and that the mass outside its orbit exerts a net zero force (using Newton's ...
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2 answers
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How can we know the velocity curve past the cut-off radius of visible matter in a galaxy?

I am trying to understand a typical explanation for the need of a dark matter halo in galaxies. The rotational velocity of stars around the centre of a galaxy seems to be constant past a certain ...
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2 answers
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Single galactic proof of Dark matter?

I've heard tell that many galaxies have visible mass profiles which do not match up to a predicted Gravitationally Newtonian velocity distribution. Can anyone here find me an accessible paper of an ...
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3 answers
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What's stopping stars in galaxy from traveling at infinite speed?

The dark matter in galaxies causes the starts to orbit with a higher orbital speed. Now, assuming that there is a constant force from the dark matter on the starts, there should be constant ...
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1 vote
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How far the galaxy's 'flat part of rotation curve' extends?

I know that the galaxy rotation curve doesn't obey general relativity and instead of decreasing, the star velocity remains constant which is shown by a flat rotation curve (rotation velocity v/s ...
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3 votes
2 answers
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Dynamical mass of a galaxy

What does the dynamical mass of a galaxy represent? Is it the mass of the gas in the galaxy or the total mass of the galaxy? What can we infer from the rotation curves, is it dynamical mass or mass ...
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0 answers
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What is the gas distribution in galaxies?

I'm fitting a number of galaxy rotation curves, and I need the density distributions of stars, gas, and DM. I know that the baryonic disk densities fall off exponentially (the characteristic radii can ...
1 vote
3 answers
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If the distribution of dark matter is not uniform, why it is not attracted towards center of galaxies?

The dark matter hypothesis was formed due to difference in theoretical and observed speed of the outer parts of galaxies. Therefore, there is more dark matter in the outer parts of the galaxy than in ...
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1 answer
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How do I decompose my overall rotation curve for M31 into a rotation curve for the disk and halo?

How do I decompose my grand rotation curve into rotation curves for the disk and halo, like the image below? The picture is from this link pages.pomona.edu/~tmoore/RotCurve The data points are ...
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1 answer
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What methods can I use to determine the total mass of M31 using rotation curve data (galactocentric radius and rotational velocities)?

I've used M(r) = RV^2/G to find the enclosed mass within the orbit of a target body in M31, but I want to use other methods to derive the total mass of the galaxy, including the mass of dark matter ...
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Questions about Dark Matter and Galactic Rotation

First, does the dark matter halo and galactic rotation of a galaxy depend on it's size? So bigger galaxies, bigger dark matter halo. Secondly, is the amount of dark matter for a galaxy universal? So ...
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Star distribution (density of stars) as a function of distance from Galaxy centre?

Is there any mathematical formula or empirical relation that defines the density of stars as a function of distance from the Galaxy centre in a spiral galaxy?
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1 answer
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Express the total mass of the galaxy in solar masses

I have the following problem: "The Sun has an orbital speed of about 220 km s−1 around the center of the Galaxy, whose distance is 28 000 light years. Estimate the total mass of the Galaxy in ...
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1 answer
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Why are galalxies spiral? [duplicate]

In every picture we see that galaxies are spiral, why so? are there any other shapes possible?
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2 answers
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Why is the distribution of dark matter in a Galaxy different from the distribution of normal matter?

The dynamics of a galaxy are driven by gravity. And dark matter experiences the same gravitational forces as normal matter. The effects of other forces are very small in comparison. So why is the ...
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3 votes
2 answers
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Why physical / cosmological models that have been falsified weren't abandoned? [closed]

Before anything, I'd like to say that I'm a layman (non physicist) and english is not my main language; I apologize if my choice of words make me sound rude / arrogant, that is not my intent. I often ...
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1 answer
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Is it possible that black holes generate space? [closed]

Suppose that there is a limit to the strength of a gravitational field. Then, if the mass is added to a black hole, the gravity term in the EFE will not increase, so the spatial expansion term must ...
0 votes
1 answer
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Gravitational potential energy of an isothermal sphere

I am trying to calculate the gravitational potential energy, W, defined as: $$W = -\frac{1}{2}\int\rho(r)\Phi(r)\mathrm d^{3}r$$ for an isothermal sphere. I am given that the density profile varies ...
3 votes
1 answer
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Why does not dark matter gather and form celestial bodies? [duplicate]

since the only thing we know about dark matter that it "attracts" and affect our Baryonic matter's momentum and speed, which means that it does have mass of a sort. so why didn't we witness a ...
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Could dark matter be normal matter that is beyond the observational horizon?

As I understand it, matter that is too distant for its light to reach us would not be observable, and the CMB is the limit of what is observable from our location within the universe. Could what is ...
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1 answer
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How do we know the quantity of dark matter in the universe?

I have been reading on dark matter and it is given specific numbers of its quantity, i.e, ~27%, in the universe. How we come up with that number as we have no strong opinion what it is made of? We ...
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