Questions tagged [galaxy-rotation-curve]

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1answer
53 views

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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2answers
1k views

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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2answers
125 views

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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1answer
50 views

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 ...
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0answers
46 views

Gravitational potential energy of an isothermal sphere

I am trying to calculate the gravitational potential energy, W, defined as: $W = -\frac{1}{2}\int\rho(r)\Phi(r)d^{3}r$ for an isothermal sphere. I am given that the density profile varies with r as:...
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1answer
118 views

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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1answer
50 views

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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1answer
56 views

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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1answer
101 views

Effects of dark matter

I was wondering, when sims of galaxies show that we need dark matter to account for the movement of outer stars, are models taking into account relativistic effects on gravity? The tips of spiral ...
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1answer
53 views

Spacetime drag and galaxies' radial velocity mismatch

We know - or theorize - that a spinning black hole drags spacetime in its surroundings, producing measurable effects on the accretion disk (the minimum stable orbit radius). What I cannot grasp is why ...
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2answers
98 views

Mass versus rotation Curves

Is there an equation that describes the relationship between the mass of the Galaxy and rotation curve? I found V versus R graphs and equations that describe their relationship (kind of). But I ...
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1answer
74 views

Can we weight dark matter?

We can observe the effect of light as it gets bended in the presence of dark matter, and I wonder how is it possible to measure their mass given that we can't see them and they don't interact with ...
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1answer
69 views

Do attraction between two galaxies count for dark matter?

We know that the uniform rotation curve of individual spiral galaxies does require presence of some form of dark entity (matter). Does the attraction between two (or more) spiral galaxies also require ...
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Could dark matter consist of the supermassive black holes at the centers of galaxies?

Inspired by this question about whether dark matter is matter, noting that dark matter tends to be clumped in galaxies near the center and less so on the edges, accepting that many (most?) galaxies ...
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2answers
198 views

What's wrong with the Big Spin Model?

A Dr. Serkan Zorba has a paper on arxiv in which he considers, what if the universe is actually slowly rotating? This gives rise to centrifugal and Coriolis forces on a galactic scale that seem to ...
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1answer
89 views

Is the dark matter present only around the galaxies?

Dark matter is believed to give galaxies its shape and prevent them from flying apart. Is dark matter present only on outer edges of the galaxy or is it present throughout the galaxy?
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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
168 views

Galaxy Rotation Speeds and General Relativity

Is it true that the predictions from the General Theory of Relativity don’t match the observations of galaxy rotation speeds, and that this then started the search for dark matter? Is it only the ...
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1answer
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Dark matter or Misunderstanding: Is it possible that the dark matter is simply missed variables in the math?

Is it possible that the dark matter is simply missed variables in the math? I am not a physicist but examples might include: effects of planetary and galaxy rotation, electromagnetic fields, ...
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2answers
131 views

How do we know that galaxies are not losing significant numbers of stars from their outer regions?

A major reason for believing in the existence of dark matter is that the stars in the outer regions of galaxies are moving too fast to remain bound to their galaxies, given only the estimated mass of ...
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1answer
122 views

Can there be forces between three things? [closed]

In all the physics I know forces are always between pairs of things. Gravity is between pairs of masses, so is electrostatic repulsion, so are the strong and weak forces as far as I understand them (...
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1answer
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How Much Do Spiral Arms Affect Their Galaxies' Rotation Curves?

According to Jerry Sellwood of Rutgers University, in the article What process creates and maintains the beautiful spiral arms around spiral galaxies?: Fortunately, nearly every one agrees that ...
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3answers
5k views

How did we 'discover' dark matter? [closed]

I'm an astrophysics student and I've been researching this topic and there is one point that keeps eluding me. How did the scientific community realize that there had to be dark matter in the ...
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1answer
471 views

What is the meaning of 'systemic velocity' of galaxies?

I came across the term systemic velocities of galaxies. Can you please explain what it means?
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1answer
57 views

Estimating total mass inside the Sun's orbit

I'm trying to estimate the local density of dark matter at a given radius, $r=R_0=8\text{kpc}$. I also have values for the core radius, $a=5\text{kpc}$, and circular velocity of the Sun, $v_{\text{...
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106 views

How is it possible to have red shift along one axis and blue shift on another in a spiral galaxy arm?

I don't understand this image: If the stars are moving in roughly circular orbits why would red shift occur in the direction of the orbit and how would it be possible to have blue shift in two ...
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Relationship between the orbital velocity of a satellite galaxy and its orbital distance

Does a satellite galaxy’s orbital velocity decrease with distance from the large galaxy, (similar to planets orbiting a star), or do they orbit faster than expected without invoking dark matter (...
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1answer
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If our galaxy's dark matter halo is so large and diffuse, why is the ordinary matter in it so much more localised and compactly located?

I just read that our galaxy's dark matter halo is estimated to be 1.5m ly across, compared to the visible galaxy's 100k ly across, needed to explain stellar rotation curves. Why would this be? By ...
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1answer
42 views

Dark matter halo distribution for simple galaxy model

It is a sufficiently well-known fact that the rotation curves of spiral galaxies are approximately flat in the middle to far regions of the disk. This is in apparent contradiction with the fact that ...
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0answers
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Milky Way: where does it end?

The milky way galaxy, as is typical for spirals (and others?), has a relatively flat rotation curve except very near the center: Eventually, at great enough distances, almost the entire mass of the ...
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2answers
243 views

“Mass Discrepancy-Acceleration Relation” in ΛCDM Paradigm

Rotation curves of galaxies seem to require more mass than observed - the conventional solution is the introduction of Dark Matter. Reading some articles on this topic (in particular a recent ...
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2answers
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Why is dark matter called dark matter?

It has been observered that spiral arm formation galaxies exist. This is a problem because due to the laws of gravitation, stars close the galactic center should orbit with a much higher angular ...
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1answer
140 views

What models do physicists use in predicting the movement of stars in a galaxy that has lead to a wide-spread conviction that Dark Matter exists?

My (possibly poor) understanding of the argument for Dark Matter's existence is that stars in a large galaxy move more slowly than "they should" (presumably due to either some simplified model of the ...
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0answers
203 views

How do you model an NFW Dark Matter Halo?

I am trying to reproduce the results of Sofue's 2016 paper (https://arxiv.org/abs/1510.05752). I'm able to use least squares minimization to model the bulge and disk effectively, but I get into ...
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2answers
414 views

Can Kepler's third law be used to find the mass of a black hole without incorporating dark matter?

Ignoring dark matter, Kepler's third law would yield different results for the mass of the black hole depending on the distance of the orbiting star from the black hole. Is it possible to make the ...
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0answers
101 views

Is there a correlation between a galaxy's rotation curve and the characteristics of its black hole?

Do galaxies with larger mass black holes have different galaxy rotation curves than those with smaller black holes? What about other characteristics, such as whether they are spinning or dormant etc?
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1answer
489 views

How are the constants for the NFW profile determined?

I'm trying to understand the NFW profile and how it causes a flat rotation curve. $$ \rho(r) = \frac{\rho_0}{\frac{r}{r_s}\left(1+\frac{r}{r_s}\right)^2} $$ I think I've got why it causes a flat ...
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2answers
7k views

Relationship between orbital radius, mass, and orbital velocity

I have a question regarding the relationship between a body's orbital radius, mass, and orbital velocity. I understand that there is the equation $V = \sqrt{\frac{GM}{R}}$, where $V$ is the orbital ...
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1answer
395 views

What is the percentage of dark matter in the galaxy? [closed]

Assuming the mass of the stars and gas within NGC 5055 is $8\times10^{10} M_{sun}$. What is the percentage of the dark matter in it?
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1answer
115 views

Why acceleration at the edge of the galaxy is lesser?

I was going through Modified Inertia using the Hubble Scale Casimir effect the theory is proposed by M.E. McCulloch. The theory says it can explain different anomalies such as EmDrive, Galactic edges,...
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1answer
313 views

Flat rotation curves and gravitational potential

I have been reading about spiral galaxies rotation curves, and I have a question I would like to clarify. For example, many of them have flat rotation curves after some characteristic distance $r>...
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1answer
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Dark matter from speed of stars in outer galaxy

My understanding is that the first evidence of dark matter came from measurements of the orbital velocity of stars in the galaxy. In theory, the further out from the centre, the slower the stars ...
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1answer
71 views

Where is the mass and gravitational influence of dark matter? [duplicate]

I'll have to ask an elementary level question about orbital motion and the mass/gravity that influences it. In solar systems, the large mass of the sun pulls on the planets and we see the velocity of ...
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3answers
150 views

What happens at the edge of a galaxy

What happens at the edge (around the optical radius) of a galaxy when it has a flat rotation curve? After some length scale: does the velocity start to decrease or is there a phase-transition-like ...
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2answers
409 views

The speed of the outer stars of galaxies [duplicate]

The stars on the outer perimeter of galaxies rotate faster than expected. Could this be because they are traveling faster in time than the center where the black hole is? I mean due to extreme ...
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1answer
66 views

Galaxy equillibrium

I know this is a very dumb question, but, to maintain a galaxy as a bounded system, the total energy and the total angular momentum of every particle component of the galaxy (suppose made of gas and ...
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2answers
228 views

Calculating orbital velocities of stars in disk galaxies

In Barbara Ryden's Intro to Cosmology, chapter 8.2, she derives and equation for the radial velocities of stars around the center of their disk galaxy. First, she states that when we look at disk ...
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1answer
74 views

Cold dark matter halos and cusps

Cold dark matter is one of the preferred candidates for dark matter. Yet, models such as the NFW and isothermal predict that halos will contain cusps, where the density tends towards infinity, despite ...
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0answers
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Galactic Rotation Curve Calculation

Can anyone give the list of formulas used for plotting the Galactic Rotation Curves? I mean, is there only the formula for linear velocity or is the formula for the gravitational potential also ...
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2answers
166 views

Questions about shape of dark matter orbits in spiral galaxies

Could someone please describe what the proposed (calculated) orbits of dark matter are? Are they exactly as those of baryonic matter (i.e. spiral), or are they different from those of baryonic matter? ...