Notices
Results 1 to 21 of 21
Like Tree1Likes
  • 1 Post By Janus

Thread: What is dark matter make of?

  1. #1 What is dark matter make of? 
    Senior Member
    Join Date
    Jul 2014
    Posts
    115
    Dark matter doesn't it neither emits nor absorbs electromagnetic radiation, it doesn't have paticle with charge. So what is Dark matter made of? And what force prevent it from collapsing into a black hole?
    Reply With Quote  
     

  2. #2  
    Senior Member
    Join Date
    Oct 2013
    Location
    UK
    Posts
    997
    No one is sure about that yet.
    Reply With Quote  
     

  3. #3  
    Banned
    Join Date
    Jul 2014
    Posts
    341
    In reply to Jilan, re: your #2 post.

    There is at least one effective definition of "dark matter"...there isn't any. It only exists as a concept to "explain things?" (such as "there isn't enough matter to account for all of the energy

    being manifested in the known Universe)


    Ta ra!
    Reply With Quote  
     

  4. #4  
    Member Janus's Avatar
    Join Date
    Jan 2013
    Location
    Portland, OR
    Posts
    71
    Dark matter comes in two types MACHO's and WIMP's

    MACHO stands for Massive Astronomical Compact Halo Objects

    Things like black holes, brown dwarfs and large planets. Stuff that is just too dim to be seen. Some but not all dark matter is likely to be this kind of stuff. Observations limit how much DM can be attributed to these types of things. Basically it comes down to the fact that if there was that much extra baryonic matter in the universe, it would effect how the rest of the visible universe evolved.

    WIMP stands for Weakly Interacting Massive Particle. A type of matter that does not interact with the electromagnetic force or radiation. Neutrinos are an example of a WIMP. While the presently known types of neutrinos are not candidates for making up DM, a hypothetical type, called a "sterile neutrino" just could be. (The "sterile" part come from the fact that unlike known neutrinos, they would not even interact by the weak nuclear interaction.)

    WIMPS don't collapse into a black hole for the same reason the stars of the galaxy don't. They have enough kinetic energy to overcome their mutual gravitational attraction.
    Reply With Quote  
     

  5. #5  
    Senior Member
    Join Date
    Jun 2014
    Posts
    551
    Quote Originally Posted by Gerry Nightingale View Post
    There is at least one effective definition of "dark matter"...there isn't any. It only exists as a concept to "explain things?" (such as "there isn't enough matter to account for all of the energy being manifested in the known Universe)
    That's taken to be the most unlikely of all hypotheses yet proposed. Some people don't like the idea of dark matter because it seems very mysterious to them and others don't like it because its seen as being something that is proposed merely to fix a theory to fit data. In fact there's very little wrong with the idea. It was our arrogance in the first place to assume that all matter can be seen using electromagnetic radiation. Especially when we already know of objects that can't be observed like that such as black holes and brown dwarfs. The expression for the gravitational force works extremely well in the domain of galactic distances so there's no reason to assume it can't work to describe the motion of material that makes up the galaxy itself.
    Reply With Quote  
     

  6. #6  
    Senior Member
    Join Date
    Jul 2014
    Posts
    115
    Quote Originally Posted by Physicist View Post
    That's taken to be the most unlikely of all hypotheses yet proposed. Some people don't like the idea of dark matter because it seems very mysterious to them and others don't like it because its seen as being something that is proposed merely to fix a theory to fit data. In fact there's very little wrong with the idea. It was our arrogance in the first place to assume that all matter can be seen using electromagnetic radiation. Especially when we already know of objects that can't be observed like that such as black holes and brown dwarfs. The expression for the gravitational force works extremely well in the domain of galactic distances so there's no reason to assume it can't work to describe the motion of material that makes up the galaxy itself.
    You mean we still don't know what it is really is?
    Reply With Quote  
     

  7. #7  
    Banned
    Join Date
    Jul 2014
    Posts
    341
    In reply to Physicist, re: your #5 post.

    "Dark matter" holds no mystery to me...it is a hypothesis. The actual "matter" may well be an allotrope of carbon, rather than more exotic particles...this would explain the "non-emission"

    status of a given structure. (this of course is predicated on the idea that there actually is "something there")

    .....

    I think the "grand assumption" that assumes "dark matter" exists is, at it's heart, a way to preserve "energy from particles" theory...a "grasping of straws" to prevent rendering energy/particle

    theories "moot" in light of the fact there are NOT enough "normal particles" to account for energy manifestation in the known Universe<(at least, this is the estimate of "how much?)


    (Thanks for reading!)
    Reply With Quote  
     

  8. #8  
    Member Janus's Avatar
    Join Date
    Jan 2013
    Location
    Portland, OR
    Posts
    71
    Quote Originally Posted by Physicist View Post
    It was our arrogance in the first place to assume that all matter can be seen using electromagnetic radiation. Especially when we already know of objects that can't be observed like that such as black holes and brown dwarfs.
    And that particles that don't interact with electromagnetism, like neutrinos do exist.

    I think that the reluctance of some to accept the idea of DM is due to, at least in part, to what I call "baryo-centrism"; the idea that since we rely on baryonic matter for our existence, it must be the dominate form of matter.
    Reply With Quote  
     

  9. #9  
    Senior Member
    Join Date
    Oct 2013
    Location
    UK
    Posts
    997
    The jury is still out on what it really is.
    Reply With Quote  
     

  10. #10  
    Senior Member
    Join Date
    Jun 2014
    Posts
    551
    Quote Originally Posted by johnzxcv View Post
    You mean we still don't know what it is really is?
    Yes.
    Reply With Quote  
     

  11. #11  
    Senior Member
    Join Date
    Jan 2013
    Posts
    354
    Quote Originally Posted by Gerry Nightingale View Post
    "Dark matter" holds no mystery to me...it is a hypothesis. The actual "matter" may well be an allotrope of carbon, rather than more exotic particles...this would explain the "non-emission"
    No, it would not explain non-emission. Carbon -- any of its allotropes -- interacts with electromagnetic radiation. It is not dark in the sense that matters. I think you misunderstand the meaning of "dark" in this context.
    Reply With Quote  
     

  12. #12  
    Senior Member
    Join Date
    Jun 2014
    Posts
    172
    The most plausible hypothesis for dark matter is that it is some kind of WIMP -- Weakly Interacting Massive Particle. But there is no suitable Standard-Model particle for being a WIMP, and all the candidates I've seen are outside the SM. However, most of them are in some extension of the SM.
    • Sterile neutrinos
    • Lightest Supersymmetric Particle
      • Lightest MSSM neutralino - in the Minimal Supersymmetric Standard Model
      • Gravitino - supersymmetric partner of the graviton
    • Axion - suppresses QCD CP violation
    Reply With Quote  
     

  13. #13  
    Senior Member MaxPayne's Avatar
    Join Date
    Oct 2013
    Location
    India
    Posts
    236
    There are two possibilities
    1) present everywhere and are made up of some kind of particle that has gravity but doesn't interact with light.
    2) made of normal matter and are located at the outskirts of galaxies but are too faint to be seen.

    I say 2.
    ┻━┻ ︵ヽ(`)ノ︵ ┻━┻
    Reply With Quote  
     

  14. #14  
    Member Janus's Avatar
    Join Date
    Jan 2013
    Location
    Portland, OR
    Posts
    71
    Quote Originally Posted by MaxPayne View Post
    There are two possibilities
    1) present everywhere and are made up of some kind of particle that has gravity but doesn't interact with light.
    2) made of normal matter and are located at the outskirts of galaxies but are too faint to be seen.

    I say 2.
    3) a combination of 1 and 2.

    But even then there is an upper limit to how much can be attributed to 2. If the total matter of baryonic matter in the universe was much greater than that which we see, the visible universe would have evolved much differently than it did. When we look out at the universe we would see something a lot different than what we see For example, if we assume a large component was made up of stellar black holes, then those black holes were formed by supernovae. But supernovae also produce heavy elements. If there were enough supernovae in the universe's early stages to create enough black holes to make up a considerable percentage of DM, then then we would have a higher percentage of heavy elements in the universe than we see now.

    That's not to say that some of DM could be attributed to this type of matter, just not all of it or even a large fraction of it.
    MaxPayne likes this.
    Reply With Quote  
     

  15. #15  
    Senior Member Boing3000's Avatar
    Join Date
    Jan 2013
    Location
    Belgium
    Posts
    194
    Quote Originally Posted by Physicist
    Some people don't like the idea of dark matter because it seems very mysterious to them...
    Indeed, and I am one of them. First the naming is plain wrong. Heavy Shadow would be a more appropriate name, or God Ultimate Puzzle, so we can start to build another more powerful useless accelerator.
    Marketing propaganda at best.

    Quote Originally Posted by Physicist
    and others don't like it because its seen as being something that is proposed merely to fix a theory to fit data
    I suppose you meant "to fix the data so they fit the theory". I thought that to be a very very bad thing to do in science.

    Quote Originally Posted by Physicist
    In fact there's very little wrong with the idea
    I agree with that, if you can at least have the slightest proposition about what idea of what "this idea" could be, and how to test it.
    Personally I think we have discover the SM to be plain wrong (I would bet on GR). No need to build another accelerator, modest telescope would do.

    Quote Originally Posted by Physicist
    It was our arrogance in the first place to assume that all matter can be seen using electromagnetic radiation
    I also think SM to be quite arrogant, but would never have dared stating it so bluntly

    Quote Originally Posted by Physicist
    Especially when we already know of objects that can't be observed like that such as black holes and brown dwarfs.
    I also found BB conjecture to be quite arrogant, like Janus said there is clear limitation on the amount of that classic cold stuff in the BB model.

    [QUOTE=lpetrich]{more real conjecture}[QUOTE]
    Isn't steril neutrino supposed to be speeding to much to clump as a hallow arround Galaxies ?

    About other SS particles, how do they fit in the BB nucleosynthesis ? Aren't they supposed to have other effects that playing the foes with our telescope ? Aren't a all bunch of those SS partners supposed to be EM active ?

    There is also nothing wrong in the hypothesis that there is nothing wrong with the SM and our telescope, and the problem is with GR which is missing 95 % of its target.

    Finally, the last hypothesis is that both SM and GR are utterly incomplete.
    Reply With Quote  
     

  16. #16  
    Junior Member PM_ME_URANUS's Avatar
    Join Date
    Aug 2014
    Posts
    6
    We are not even sure if the Dark Matter we see is just one unknown type of matter
    Reply With Quote  
     

  17. #17  
    Senior Member MaxPayne's Avatar
    Join Date
    Oct 2013
    Location
    India
    Posts
    236
    We don't see dark matter.
    ┻━┻ ︵ヽ(`)ノ︵ ┻━┻
    Reply With Quote  
     

  18. #18  
    Junior Member PM_ME_URANUS's Avatar
    Join Date
    Aug 2014
    Posts
    6
    yea I know
    Reply With Quote  
     

  19. #19  
    Junior Member
    Join Date
    Sep 2014
    Posts
    3
    One solution, there is no dark matter, but the Big Bang correspond to a time-Way black hole.
    The dark energy is curvature of this black hole .
    Reply With Quote  
     

  20. #20 Dark matter is ambiguous 
    Junior Member
    Join Date
    Aug 2017
    Posts
    3
    Well, maybe we dont even know if there is some matter or not.
    We have assumed that. We believe that some hidden sort of matter exists that can account for the 'unknown gravity that we have observed'. You may call it dark GRAVITY....bcoz there is some unknown dark matter, this conclusion has been deduced (i think) from the fact that there is some gravity in a galaxy that does not have a known source. Well, due to this position of dark matter in our understanding, makes it difficult to reveal anything about its nature......maybe no one knows what dark matter consists of.... there may be dark atoms, dark molecules, etc but again all this is just another thought.....
    Reply With Quote  
     

  21. #21  
    Senior Member
    Join Date
    Jan 2013
    Posts
    354
    Quote Originally Posted by Gaurav(-26.7) View Post
    Well, maybe we dont even know if there is some matter or not.
    We have assumed that. We believe that some hidden sort of matter exists that can account for the 'unknown gravity that we have observed'. You may call it dark GRAVITY....bcoz there is some unknown dark matter, this conclusion has been deduced (i think) from the fact that there is some gravity in a galaxy that does not have a known source. Well, due to this position of dark matter in our understanding, makes it difficult to reveal anything about its nature......maybe no one knows what dark matter consists of.... there may be dark atoms, dark molecules, etc but again all this is just another thought.....
    No one knows what the composition of dark matter is. However, you somewhat misstate the evidence for its existence. It's not just "a galaxy", it's that all spiral galaxies that have been studied exhibit rotation curves that do not behave as expected. If you add matter, the discrepancies disappear. Trying to adjust gravity itself (search for MOND, for example) can fix that problem, too, but it creates new ones. So, of the proposed mechanisms, dark matter is currently the best candidate, because it fixes more than it breaks, so that's the favoured hypothesis. As more evidence pours in, from astronomical observations as well as experiments here, the hypothesis will either be strengthened or a better candidate may emerge. These are exciting times!
    Reply With Quote  
     

Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •