Dark Matter, what is it?

[vincent]

Well?

[cchasem]

Just rogue planets / asteroids. Large collections of random junk in space orbiting around nothing/itself with no suns nearby.

[vincent]

Just rogue planets / asteroids. Large collections of random junk in space orbiting around nothing/itself with no suns nearby.

586705695[/snapback]

Nope.

[ev0|]

Lol, ripgut, if you have an idea, at least post your own theory in there too....

[vincent]

Well from what i've gathered is that Dark Matter , rather it's particles cannot be detected but rather it presence is noticed in things like large scale structures in the universe; what holds galactic clusters together; galactic rotational curves; gravitational lensing, and a few other things.

[cchasem]

That's exotic dark matter.

[raid517]

As of this point in time, it is gallactic green cheese. We don't really have a better explanation for it than that. Im not saying I don't believe in it, but until we can pin it down, or come up with a better theory, I will remain skeptical. As a rule of thumb, if the universe says your calculations are wrong, generally it isn't the Universe who is wrong.

GJ

[j.nudd]

It is the 96% of the universe's mass that we cannot account for by methods we are aware of.

[vincent]

As of this point in time, it is galactic green cheese. We don't really have a better explanation for it than that. Im not saying I don't believe in it, but until we can pin it down, or come up with a better theory, I will remain skeptical. As a rule of thumb, if the universe says your calculations are wrong, generally it isn't the Universe who is wrong.

GJ

586706880[/snapback]

I agree however there is some information i've read that points to evidence of "dark matter" there. For instance, in clusters of galaxies. Here is an interesting paper on Dark Matter and the evidence taht points to its presence.

http://www.astro.queensu.ca/~dursi/dm-tutorial/dm1.html

[_sphinx_]

Its like the blood of the universe, it contains dark evergy and it constitutes to 80+& of the universe's mass...It is endless and very little is known about it because it is invisible since it doesn't reflect or emit light. Its aonly a theorm that dark matter is the base of the universe...The glue that holds it all together....Just a theorem. I don't study astrophysics but dark energy camE up while I was studying Einstein's e=mc^2

[raid517]

I agree however there is some information i've read that points to evidence of "dark matter" there. For instance, in clusters of galaxies. Here is an interesting paper on Dark Matter and the evidence taht points to its presence.

http://www.astro.queensu.ca/~dursi/dm-tutorial/dm1.html

586710523[/snapback]

I never said there was no evidencefor it - indeed given current calculations there is an abundance of evidence for it. But dark matter is not a hypothesis we can test yet - and until it can be tested there is a requirement - indeed an absolute scientific imperative to remain skeptical.

We cannot call things science that we cannot test, or that we cannot directly observe.

At this point it is an interesting hypothesis - but nothing more than that.

GJ

[vincent]

I never said there was no evidencefor it - indeed given current calculations there is an abundance of evidence for it. But dark matter is not a hypothesis we can test yet - and until it can be tested there is a requirement - indeed an absolute scientific imperative to remain skeptical.

We cannot call things science that we cannot test, or that we cannot directly observe.

At this point it is an interesting hypothesis - but nothing more than that.

GJ

586711006[/snapback]

Thats makes alot of sense :)

[LOC Veteran]

In cosmology, dark matter refers to hypothetical matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. The dark matter hypothesis aims to explain several anomalous astronomical observations, such as anomalies in the rotational speed of galaxies (the galaxy rotation problem). Estimates of the amount of matter present in galaxies, based on gravitational effects, consistently suggest that there is far more matter than is directly observable. The existence of dark matter would also resolve a number of inconsistencies in the Big Bang theory, and is crucial for structure formation.

If dark matter does exist, it vastly outmasses the "visible" part of the universe [1]. Only about 4% of the total mass in the universe (as inferred from gravitational effects) can be accounted for. About 23% is thought to be composed of dark matter. The remaining 73% is thought to consist of dark energy, an even stranger component, distributed diffusely in space, that probably cannot be thought of as ordinary particles. Determining the nature of this missing mass is one of the most important problems in modern cosmology.

That's taken from Wikipedia, and is pretty spot on.

There's currently 3 types of "accepted" Dark Matter, Hot Dark Matter, Cold Dark Matter and Baryonic Dark Matter (the last having to do with Baryon particles).

[futb0l]

'Hypothetical Matter Particles'... This theory just seems strange to me, there must be something more to it.

[Dave Veteran]

There's currently 3 types of "accepted" Dark Matter, Hot Dark Matter, Cold Dark Matter and Baryonic Dark Matter (the last having to do with Baryon particles).

586713825[/snapback]

Now I'm curious. What are the differences between the three?

[dreamz Veteran]

Now I'm curious. What are the differences between the three?

586731785[/snapback]

cold dark matter consists of heavy particles moving at sub-relativistic velocities. hot dark matter is constituted by particles with small mass moving at high speeds.

baryonic dark matter encompasses baryonic particles (i.e. those particles that include protons and neutrons) that do not emit light.

here's a brief explanation: http://archive.ncsa.uiuc.edu/Cyberia/Cosmo...reMeetsEye.html

[guru]

dark matter is a theory to account for the "missing mass" in the universe.I rememeber reading somewhere that if nuetrinos have mass. that'd account for the missing matter

[dreamz Veteran]

dark matter is a theory to account for the "missing mass" in the universe.I rememeber reading somewhere that if nuetrinos have mass. that'd account for the missing matter

586789015[/snapback]

according to the various calculations, neutrions may or may not resolve this issue.

[Beastage]

LOC said it all... its there we can't see it we can't detect it but we can see it effects

[ev0|]

the "90 precent of the universe mass causing" Dark Matter/Energy paricles are NON-BARYONIC and we can't "see" them because they don't emit light, if they exist... but something must account for the mass to make the universe look and behave the way it does... unless we are wrong, fundamentally about the universe.

Plus... this is 2005....not 2756... who knows

[vincent]

Hubble Sheds Light on Dark Matter

Astronomers don?t know what it is, but every now and then they find more evidence of dark matter and pin down where the mysterious stuff resides.

A new project that recycled Hubble Space Telescope images has mapped the invisible dark matter with unprecedented detail. Researchers focused on two galaxy clusters that are so far away, and their light has taken so long to get here, that they are seen as they existed when the universe was about half its present age.

The observations provide additional evidence supporting a leading theory that galaxies form in cosmic webs, with regular material and dark matter condensing into nodes something like water drops gather at intersections of spider silk.

You can also think of it as froth gathering on the tops of ocean waves, said study team member Myungkook James Jee at Johns Hopkins University.

Strange stuff

Dark matter is thought to exist because without it, galaxies would fly apart for lack of gravitational glue. However mapping something that can?t be seen is problematic.

"It is very challenging to verify the simulation results observationally, because dark matter does not emit light," Jee said.

The trick is to look for subtle distortions in the images caused by gravitational lensing, in which the shapes of very distant galaxies are warped by dense concentrations of matter between us and the galaxies. The matter, which is not visible, bends the light with its gravity, and that reveals its presence.

"The images we took show clearly that the cluster galaxies are located at the densest regions of the dark matter haloes, which are rendered in purple in our images," Jee said.

The results are detailed in the December issue of Astrophysical Journal.

Dark matter makes up about 90 percent of the universe?s total. Theory holds that it should gather with regular matter, because of their mutual effects of gravity. The new observations support that idea, Jee said.

The work also supports the notion that dark matter is not made of particles that can collide. It?s not known if dark matter involves particles at all, but if so, they must be collisionless.

"Collisionless particles do not bombard one another, the way two hydrogen atoms do," Jee said. "If dark matter particles were collisional, we would observe a much smoother distribution of dark matter, without any small-scale clumpy structures."

The two clusters each contain more than 400 galaxies.

"These images were actually intended mainly to study the galaxies in the clusters, and not the lensing of the background galaxies," said co-researcher Richard White of the Space Telescope Science Institute, which operates Hubble for NASA. "But the sharpness and sensitivity of the images made them ideal for this project. That's the real beauty of Hubble images: They will be used for years for new scientific investigations."

source

[j.nudd]

That whole article you posted is very interesting. I find it somewhat ironic that the dark matter particles that don't emit light themselves have a profound effect on light as it travels to us.

[raid517]

As does all mass.

GJ

[vincent]

As does all mass.

GJ

Yup, according to GR all matter bends the fabric of space-time, causing light to bend.