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9
votes
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 ...
2
votes
2answers
122 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 ...
3
votes
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 ...
-3
votes
1answer
49 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 ...
0
votes
1answer
55 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 ...
1
vote
1answer
100 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 ...
2
votes
1answer
73 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 ...
1
vote
1answer
68 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 ...
7
votes
4answers
3k views

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 ...
1
vote
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?
1
vote
0answers
19 views

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 ...
3
votes
1answer
159 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 ...
0
votes
1answer
69 views

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, ...
2
votes
2answers
129 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 ...
15
votes
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 ...
0
votes
1answer
56 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{...
0
votes
0answers
64 views

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 (...
12
votes
1answer
2k views

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 ...
0
votes
1answer
41 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 ...
3
votes
0answers
115 views

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 ...
3
votes
2answers
242 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 ...
0
votes
2answers
371 views

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 ...
0
votes
1answer
139 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 ...
1
vote
0answers
201 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 ...
1
vote
2answers
412 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 ...
2
votes
1answer
483 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 ...
4
votes
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 ...
-3
votes
1answer
392 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?
1
vote
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,...
0
votes
1answer
308 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>...
-1
votes
1answer
143 views

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 ...
0
votes
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 ...
3
votes
3answers
148 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 ...
2
votes
2answers
397 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 ...
3
votes
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 ...
1
vote
0answers
104 views

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 ...
3
votes
2answers
165 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? ...
5
votes
3answers
795 views

How to explain two possible problems with dark matter

Can someone please answer how dark matter theory resolves/eliminates these two possible problems Dark matter, per my understanding, due to gravity, keeps moving, and due to its non-interactive nature,...
-4
votes
4answers
595 views

Is dark matter really there? [closed]

Dark matter has been proposed to explain two phenomena - Uniform velocity curve of spiral galaxies Observed gravitational lensing. If something explains these two, would we still need dark matter? ...
2
votes
2answers
423 views

Does Newtonian physics work on a galactic scale?

I'm currently working on a simulation that aims to use Newton's Law of Gravitation to simulate how a galaxy behaves gravitationally. While I haven't gotten the simulation finished yet, I have had a ...
76
votes
5answers
9k views

If dark matter only interacts with gravity, why doesn't it all clump together in a single point?

I'm a complete layperson. As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, ...
2
votes
0answers
140 views

Bulge-Disk decomposition in galaxies

I'm starting a new project on dark matter astrophysics in which I have to extract from some data (I will write some below) the surface brightness, to later construct the mass density profiles of de ...
4
votes
1answer
132 views

How dark matter makes ordinary matter far from the center of a disc galaxy rotate faster?

I was reading several questions on this subject, incluiding duplicates, and even received the very useful help of Kyle Oman in this question to understand the behavior and distribution of DM. But I'm ...
1
vote
1answer
527 views

Density of dark matter along the galaxy [duplicate]

I was reading these 2 interesting articles about dark matter inside the solar system: Does Dark Matter affect the motion of the Solar System? The Incredible Dark Matter Mystery: Why Astronomers Say ...
4
votes
4answers
720 views

How can I add dark matter to my $N$-body simulation?

I've written a simple non-scientific N-body simulation for fun: http://magwo.github.io/fullofstars/ I expected to create something looking like spinning galaxies (there are two invisible very heavy ...
1
vote
0answers
87 views

Why do planets moving around our Sun lead to how stars move around the centre of a spiral galaxy?

We know that the speed with which the planets go around our sun decreases as a function of the distance they are from the sun. Since stars are not planets, and presumably do not behave like planets, ...
1
vote
2answers
319 views

Missing Matter Problem and Galactic Kinematics

This is a re-wording of an earlier problem I posted. The standard example of the Missing Mass Problem comes from the rotational profiles of galaxies. By counting up the visible matter, we extrapolate ...
1
vote
1answer
275 views

Galaxy rotation curve [duplicate]

In calculating galaxies' rotation curve, it is assumed that masses outside the orbit has no contribution and masses inside the orbit can be deemed as if they were at the center, just like the case of ...
1
vote
2answers
412 views

Relativity and Galaxy Rotation Speed

If time travels slower nearer gravity wells, why can't the galaxy rotation speeds being faster on the outer edges than the inner areas be explained by relativity? What necessitates dark matter?
14
votes
2answers
1k views

What is a reasonably accurate but simple model of the Milky Way's gravitational field?

I am putting together a toy program which shows how stars move around in the galaxy. To run the simulation I need to know strength of the Milky Way's gravitational field at any location in it. I'm ...