Concepts

[GreenAce92]

Gahh I feel like I already posted this and it didn't show up or something...
Anyhow first of all what is the dark stuff in space called, Dark matter? Not dark energy? Sorry if that's a dumb question.

I had an idea on if something reacted with this dark stuff, that we could have like say a "plasma propeller" or something that reacted with the dark matter in space and thus treated it like air...

Also I was wondering about the force of the solar winds/flares in space, like I know that the earth has its own Magnetic field protecting us from such things, but I've read a few times on solar sails harvesting this energy, I think it said that it's very weak but it builds up slowly, sort of similar to Ion engines... weak but builds up because of no friction.

Ahh I've got more but I have to remember them, I could've sworn I have just posted this.

 

[Gravity_Ray]

Dark matter and Dark energy are not things per se. The word dark is used as a place holder, science talk for "we dont know".

The word dark matter means "something" we dont know what, that is holding matter together in space. For example a spinning galaxy should fly apart, but it doesnt. Something is holding it together. Also the stuctures in the universe (like galaxies) seem to form in clumps around something. This something is called dark matter. However, it is so non-reactive with anything else that in the small sense it might as well not be there. It only seems to work its magic with very large structures. So I dont believe there is anything that people know about (your example a "plasma propeller") that can react with it. If you figure out something that will, you have a nobel peace prize comming.

The word dark energy means "something" we dont know what, that is making the universe continue to expand (and expand faster). Which doesnt make alot of sense if you think of the big bang as the explosion OF space (not in space). At some point things should slow down, but right now the universe' rate of expansion is rising. So some energy is puling the universe apart. That is called dark energy.

These are simple explanations, but both of these things are just ideas not actual things. So we can not really interact with them (yet).

I think that solar sails are a great idea and should be used more often by us. You can actually see the solar wind in action everytime a commet gets into our solar system. The commets tail.

 

[GreenAce92]

The comet's tail shows solar winds? Or the solar sail? How so? I thought it was just breaking up of the comet, or are you saying that these "space contrails" get displaced or changed ie go from being straight to squiggly...

Thanks for the clarification, it's not gravity holding the galaxy's together?

 

[Gravity_Ray]

The comet's tail shows solar winds? Or the solar sail? How so? I thought it was just breaking up of the comet, or are you saying that these "space contrails" get displaced or changed ie go from being straight to squiggly...

Yes a comets tail shows the solar wind. The sun is ejecting heat (solar radiation), this energy is traveling pretty fast (much faster than a comet). When the comet which is basically a ball of frozen ice and dust gets close to the sun it heats up and develops a coma (the material of the comet vaporize and stream out of the nucleus. As the suns energy hits these vaporized materials it pushes them away from the sun, so the tail of a comet always points away from the sun regardless of where the comet is going. Its called the solar wind, not the solar sail. A solar sail will be a sheet of material that can be put on a space ship and used like a regualr sail on a boat to catch the energy of the sun and have it push your space ship around like it pushes the comets tail around. Thus moving in space.

Thanks for the clarification, it's not gravity holding the galaxy's together?

Think of dark matter as holding the structure of a galaxy together, and think of gravity as the force that is acting on all the material in that galaxy. As I said dark matter is only really observable in very large structures (galaxy size and larger). Ultimately though nobody knows what in the world dark matter is. So this is all speculation.

 

[MeteorWayne]

Hopefully a little helpful clarification.

The yellowish tail of a comet is the dust released from the nucleus being pushed away by the solar wind.

As far as dark matter, galaxies are spinning so fast, that if only the visible matter (stars, dust and gas) was providing all the gravity, they would fly apart. So there must be invisible matter (dark matter) providing extra mass, to supply the extra gravity to keep them together. There are another half dozen gravitational effects that show that dark matter exists (gravitational lensing, CMBR. galaxy clusters, etc)...we just aren't sure what "it" is yet, so we call it dark matter.

There are several searches under way for the potential particles.

 

[Solifugae]

Why is "dark matter" assumed to be exotic, and not unseen visible matter such as vast and dark clouds of dust and innumerable dim brown dwarfs?

 

[ramparts]

There's a couple of answers to that. For brown dwarfs, people did think, a couple of decades back, that they might make up the dark matter. We've gone out and looked at brown dwarf populations, and there simply isn't enough out there. It's highly unlikely.

The other important consideration is that brown dwarfs and dust will act like normal matter, and the dark matter most certainly does not. The emission of light is one thing (dust, for example, will certainly be illuminated by background light). But more important is the interactions. Clouds of "normal matter" like brown dwarfs or dust grains or gas will behave in certain ways - exhibiting friction and other complicated gas dynamics. Dark matter does not do this. Observations confirm this; we actually have observed galaxy clusters in the process of colliding where the dark matter separates from the normal matter because it doesn't experience these dynamics (look up the Bullet Cluster). It's also theoretically important that dark matter only interact gravitationally (these gas dynamics come from electromagnetic forces and the like), because if it didn't, then galaxy clusters wouldn't be able to form. Dark matter is crucial for our picture of the formation of structure in the Universe, and this really doesn't work if dark matter is made of normal "stuff."

 

[GreenAce92]

Could we use an analogy and say that "dark matter would be like the water holding the particles/sediments together while the solute and solvent spin and the solute doesn't fly off"... I guess would that be correct or not? Think of say "thick oil of some sort and iron filings (got this from a youtube video quick magnetic field visual)

Dark matter is what "fills the background/major gaps?
Thanks for your time guys and efforts in explaining this stuff, I appreciate it

the "sails" part up there was a typo too sorry I should really read what I type.

 

[neilsox]

Why is "dark matter" assumed to be exotic, and not unseen visible matter such as vast and dark clouds of dust and innumerable dim brown dwarfs?

If there were enough brown dwarfs, rogue planets, comets, asteroids, dust and black holes without significant accretion disks to account for the apparently missing mass, our galaxy should be less transparent to photons. Also the stuff should pass though the inner solar system frequently, but we have had close to zero galactic visitors the last two centuries. Possibly this is an atypical lull in galactic visitors, but exotic dark matter seems a better explanation. Neil

 

[acsinnz]

Ramparts "It's also theoretically important that dark matter only interact gravitationally (these gas dynamics come from electromagnetic forces and the like),"
Yes, I agree that its something to do with electromagnetics in space. There has to be electrics fields in space and these are definitely having an effect on the formation of stars and the dark matter planets/debris in space.
CliveS