Dark Matter density given specific location

[RyanH42]

I am doing research and I need to find the dark matter density of Galaxies or dust clusters (It can be any type of thing) which the distance from Earth will be ≅4000 Mpc.Here the picture
Think the radius of sphere.

 

[Mordred]

I am doing research and I need to find the dark matter density of Galaxies or dust clusters (It can be any type of thing) which the distance from Earth will be ≅4000 Mpc.Here the picture
Think the radius of sphere.

I'm not sure how you would go about it from the Earth as a reference point, however the NFW profile will probably do from galactic center.https://en.m.wikipedia.org/wiki/Navarro–Frenk–White_profile

 

[Mordred]

Edit I don't think that formula will work at 4000 Mpc. I'm pretty sure it won't, as the galaxy is only 30 kpc. Sounds like your looking for the average dark matter density.

https://en.m.wikipedia.org/wiki/Lambda-CDM_model which the Planck 2013 can be found here

 

[RyanH42]

I looked my equations and I saw a mistake.Thanks for replying again.The distance will not be 4000Mpc.I am working on it If I find the right solutiion I will going to ask again

 

[Chronos]

Dark matter mapping is typically conducted via gravitational lensing

 

[RyanH42]

Is there any dark matter where no baryonic matter.I mean are we observe dark matter only around the matter ? Or dark matter can be anywhere(In empty space which there's no baryonic matter around)

 

[mfb]

It's the other way round - matter tends to accumulate where (the more frequent) dark matter is. Baryonic matter accumulations tend to be more concentrated, so just outside galaxies (and even outside the disk of spiral galaxies) you have a significant dark matter density but a low density of baryonic matter.

 

[phinds]

Just to add to what mfb said, there's nothing to say that there is not some cluster of dark matter somewhere that has little or no baronnic matter in the cluster. I'm not at all suggesting that this is likely, just that I'm not aware of any reason why it would not be possible. If there were such a cluster it would be pretty much impossible to detect although if it were a big enough cluster and we knew exactly where to look for it, we might see it through gravitational lensing.

 

[newjerseyrunner]

Dark matter causes the structure of matter, not the other way around. I tend to think of galaxies not as swirling pockets of stars but as a vast cloud of dark matter with a small pocket of matter bobbing around inside of it.

 

[RyanH42]

If that's true (matter goes where there's dark matter) then I have a question (This question can be also ask when BM attracts Dark matter-which I learned that's not possible- ).My question will be how can dark matter and baryonic matter can be same place without any interaction.

I want to give an example consider a massive star and a planet.And If planet is close enough to sun then the planet will be fall into the sun.So sun here DM and planet is BM.Dark matter curves space-time and makes a dense place.As this place DM attracts BM.So they must be interact somehow but there's not interaction ? Why I think there must be an interaction.Cause there's a force of gravity right.If Earth pulls meteorite,meteorite should fall into earth.So If BM fall this dense area then İt mmust be contact somehow with dark matter.

I hope I clarify myself

 

[mfb]

(This question can be also ask when BM attracts Dark matter-which I learned that's not possible- )

Both attract each other.
We have 5 times more dark matter than baryonic matter. It's like attaching an RC car to an actual car via a string. Sure, the RC car has its own motor, but the system will go in whatever direction the car moves.

My question will be how can dark matter and baryonic matter can be same place without any interaction.

Where is the problem? They interact via gravity and maybe via the weak interaction, but not via anything else. The weak interaction is negligible, and the interaction via gravity is relevant at the scale of galaxies only.

The planet that falls into the sun is stopped there via the electromagnetic interaction. A dark matter particle will just move through the star and continue to fly through space, just with a slightly different direction due to gravity.
A tiny fraction of dark matter particles could interact via the weak interaction - that's what experiments on Earth try to see.

 

[newjerseyrunner]

It's possible for dark matter to not even interact with itself.

 

[RyanH42]

A tiny fraction of dark matter particles could interact via the weak interaction - that's what experiments on Earth try to see.

In general we won't expect any interaction but somehow we expect a little bit interaction which we want to see in experiments

 

[newjerseyrunner]

In general we won't expect any interaction but somehow we expect a little bit interaction which we want to see in experiments

I'm not sure if scientists expect it or not, it's just something that we could theoretically observe, so they are checking on it. The weak interaction would cause the dark matter to decay, creating antimatter, which will produce a gamma ray photon of a very specific energy.

No one said dark matter is not expected to interact with anything, they only said it doesn't seem to interact with matter and the electromagnetic forces, which are a small fraction of the universe.

 

[RyanH42]

The weak interaction would cause the dark matter to decay, creating antimatter, which will produce a gamma ray photon of a very specific energy.

How can this decay can be possible ? If DM decays anti mattter then we have to seen it already.But we didnt observe such a thing.I am wrong ?

 

[RyanH42]

Why it should be matter it can't be an energy ? A energy which never interects with matter ? Thats the reason why we can't see it ?

 

[newjerseyrunner]

How can this decay can be possible ? If DM decays anti mattter then we have to seen it already.But we didnt observe such a thing.I am wrong ?

Not sure, probably some assumed symmetries and conservation of certain quantum numbers. I'd not be the best to explain why this might be expected.

Why it should be matter it can't be an energy ? A energy which never interects with matter ? Thats the reason why we can't see it ?

Because dark matter is known because of it produces gravity, only things with mass produce gravity. Remember that matter is energy.

There is still way too much that isn't known to give you any good answers, when you are almost completely ignorant of something, all possibilities are valid. The whole thing could be an illusion caused by our formulas being wrong. Could be a fleet of Death Stars. All we can say is what it's not: It's not neutrinos, it's not black holes...

 

[RyanH42]

A mystery

 

[RyanH42]

Thank you guys

 

[mfb]

It's possible for dark matter to not even interact with itself.

Well, at least gravitationally it has to.

There are four main ways dark matter can be detectable:
- it could decay with a very long lifetime (much longer than the age of the universe - after all, it is still there) to known particles like photons, electrons, muons, quarks and so on. The decay has to be mediated by the weak force or some yet unknown mechanism, as the dark matter particles do not couple to the strong and electromagnetic interaction directly. The detection would happen via telescopes and particle detectors in space.
- it could annihilate with other dark matter particles. Not a decay in the strict sense, but it gives a signature very similar to decays. The "effective lifetime" depends on the dark matter density then, but it has to be much longer than the age of the universe again.
- it could interact with matter in underground detectors. The most likely interaction is elastic - we would just see a "kick" for some particle in the detector without a visible cause.
- it could be produced in particle accelerators. The detectors wouldn't detect the dark matter directly, but it would be notable as an imbalance in the observed transverse momentum of the visible particles (simplified: we see the recoil with known particles on one side, but not the produced dark matter going to the other side)

If DM decays anti mattter then we have to seen it already.

What do you mean with "if DM decays anti matter"?

Why it should be matter it can't be an energy ?

Why does it have to be a banana why can't it be yellow? Matter has energy, this is not "one or another".

only things with mass produce gravity.

This is not true. Energy is the source of gravity, not matter. Mass has energy, but light and motion has energy without mass.

 

[RyanH42]

The weak interaction would cause the dark matter to decay, creating antimatter, which will produce a gamma ray photon of a very specific energy.

The reason which I said that sentence.

Matter has energy yes.But we are always thinking DM like a particle but maybe its not a particle.Think dark energy we seem it like an energy.The space-time vacuum energy.So maybe DM can be sort of something like that.
But I again you are righy I guess.My idea looks like stupid.

If there's anti DM, and DM decays antimatter, then If anti DM decays we will get matter.Which it explains why there's dark matter no anti DM and no anti mattet ?

 

[mfb]

Do you mean "DM decays b]to[/b] antimatter"? There is no particular reason why it should do that. Detecting antimatter is easier in our universe as there is a lower background.
"Dark matter" is not grouped into matter and antimatter. Whatever is there is called dark matter. It could even be a particle that is its own antiparticle.

There are good indications that dark matter behaves like particles moving around.

 

[RyanH42]

Yes DM decays to anti matter.I see If its even correct we cannit prove anyway.We disnt even know "dark matter".I just told my idea.
Thanks

 

[mfb]

Yes DM decays to anti matter.

Maybe. We don't know.

I see If its even correct we cannit prove anyway.

Maybe.

We disnt even know "dark matter".

Oh well, we know it exists and we can see its gravitational influence.

 

[newjerseyrunner]

I meant that if it decayed it most likely decayed into a particle and an antiparticle, which should annihilate, I didn't mean to specify antimatter.

It's also conceivable that dark matter simply won't fit in with the way we currently understand the universe. Considering that dark matter requires both gravity and some sort of particle physics, we may not be able to figure out what it is until we unify the theories. That's why I'm so excited by the prospects of LHC looking for it, if we could observe some of it's other effects it might give someone the insight required to create the next paradigm in physics. Dark matter may have gone through a completely different evolution after the gravity and the other forces split, it could have it's own weird forces too.

 

[mfb]

Dark matter "requires" gravity in the same way a proton "requires" gravity. Both have energy, so both interact gravitationally. No magic involved.
It is unlikely that dark matter particles pop up in a theory that unifies gravity with the other forces. The energy scales just don't fit.

Any dark matter - dark matter interactions have to be weak (as in "not strong"), as DM doesn't clump in the same way matter does.

 

[ohwilleke]

There are four main ways dark matter can be detectable:
- it could decay with a very long lifetime (much longer than the age of the universe - after all, it is still there) to known particles like photons, electrons, muons, quarks and so on. The decay has to be mediated by the weak force or some yet unknown mechanism, as the dark matter particles do not couple to the strong and electromagnetic interaction directly. The detection would happen via telescopes and particle detectors in space.
- it could annihilate with other dark matter particles. Not a decay in the strict sense, but it gives a signature very similar to decays. The "effective lifetime" depends on the dark matter density then, but it has to be much longer than the age of the universe again.
- it could interact with matter in underground detectors. The most likely interaction is elastic - we would just see a "kick" for some particle in the detector without a visible cause.
- it could be produced in particle accelerators. The detectors wouldn't detect the dark matter directly, but it would be notable as an imbalance in the observed transverse momentum of the visible particles (simplified: we see the recoil with known particles on one side, but not the produced dark matter going to the other side)

I guess it depends on how you define "detectable", but the primary ways to detect dark matter are (1) to infer them from the gravitational dynamics of ordinary matter particles that are observable, and (2) to observe when doesn't happen when gravitational dynamics are observed would lead to discernible interactions if caused by ordinary matter that isn't luminous (e.g. hydrogen gas in interstellar space or dust). You can tell a lot about the inferred velocity of dark matter particles and dark matter's inferred density per volume in particular places from these methods, particularly as you get to a fine toothed level such as looking at the dynamics of stars outside the main disk in a spiral galaxy.

While strictly speaking not different from (1), another technique is to assume that dark matter of a particular type exists, run a simulation of the universe's lifetime, see what the universe looks like, and compare it statistically to the universe we observe (basically on the theory that the closer your hypothesis is to reality the better the simulation will match the model).

 

[mfb]

Detectable as particles, so I didn't include the gravitational influences in the list.