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  1. #1
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    Default Dark matter contribution to black hole creation.



    Basically what the title say. I would assume dark matter's
    contribution to massive stars whit enough solar masses
    to leave a black hole behind after a supernova would be
    considerable, in regards to the estimated dark matter to
    visible matter ratio.

    What is your opinion and thoughts about this?

    (DanielC could you make some modifications to the simulator you use
    for your thesis to help us out here?)


    Regards



    Dustworm

  2. #2
    Joe Lalumia's Avatar
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    Lately there have been observations that place the number of dwarf (cold) stars and rouge planets much higher than we used to think--

    This may account for much more of the "missing" mass associated with galaxies.

    Truly surprising science discovery – free floating planets | Watts Up With That?

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    Default

    Quote Originally Posted by Dustworm View Post
    Basically what the title say. I would assume dark matter's
    contribution to massive stars whit enough solar masses
    to leave a black hole behind after a supernova would be
    considerable, in regards to the estimated dark matter to
    visible matter ratio.

    What is your opinion and thoughts about this?

    (DanielC could you make some modifications to the simulator you use
    for your thesis to help us out here?)
    I wish it was considerable, because that would be really cool, but unfortunately it is not. The amount of WIMPs captured by a star even in the best case scenario is really tiny. There are two reasons for this: First, the galaxy is a big place, and not very dense. The amount of WIMPs going through the Sun is not very large to begin with. Second, WIMPs are very difficult to capture. My simulations suggest that something in the region of 1 WIMP in 10,000 might be captured (the actual value depends on the speed of the star). So the mass contribution is very tiny.

    What I'm hoping for in my research is that even a tiny WIMP mass will be detectable through other means. When a star captures WIMPs, it gets free energy because they WIMPs can annhilate each other. If the star gets enough free energy, that will change the star's structure and how it evolves, making it live much longer, and that's something we could detect.

    My research is to try to figure out where we have the best shot of finding a star like that.
    Astronomer. Lund Observatory

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    Quote Originally Posted by Joe Lalumia View Post
    Lately there have been observations that place the number of dwarf (cold) stars and rouge planets much higher than we used to think--

    This may account for much more of the "missing" mass associated with galaxies.
    The free floating planets would not contribute significantly to the mass of the galaxy. A Jupiter type planet has 1/1000th the mass of the Sun, so having one more planet for every star doesn't really add much to the mass of the galaxies.

    However, the one about red dwarfs is very interesting for dark matter. Most stars are red dwarfs, so if there are more red dwarfs that can affect the baryonic mass of the galaxy a fair bit. That said, I'm not really sure how much this affects dark matter. We already knew that there was more baryonic mass in the universe than we could detect, this is the "missing baryons" problem. So what I suspect is that the new red dwarfs only go to solve the missing baryons problem, without doing quite as much to solve the dark matter problem. But I haven't read this research yet, so I might be wrong.
    Astronomer. Lund Observatory

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  7. #5
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    The article suggests as many rouge planets as stars in the galaxy. It will be interesting to see how this affects the calculation of mass -- this plus the dwarf stars... ?

    But it is still not enough to disprove dark matter.
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    Quote Originally Posted by DanielC View Post
    My simulations suggest that something in the region of 1 WIMP in 10,000 might be captured (the actual value depends on the speed of the star). So the mass contribution is very tiny.

    What about a black hole, could it possibly catch and contain a much larger
    amount of WIMP's?



    Regards


    Dustworm

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    Neutrinos could be dark matter if they don't interact through the weak force........however......we would need a tremendous amount of them to fill the missing mass...?

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    Quote Originally Posted by Joe Lalumia View Post
    The article suggests as many rouge planets as stars in the galaxy. It will be interesting to see how this affects the calculation of mass -- this plus the dwarf stars... ?

    But it is still not enough to disprove dark matter.
    As I said earlier, the mass of a Jupiter-type planet is 1/1000th the mass of the Sun. So adding one Jupiter type planet for every star in the galaxy does not really increase the mass of the galaxy by any significant amount. The discovery of rogue planets is extremely interesting, but it has nothing to do with dark matter.

    The one about dwarf stars is a lot more related to dark matter because dwarf stars are by far the most common. So that discovery has the potential to affect the amount of dark matter needed. But don't forget that we already knew that the universe has about 2 times more baryonic matter than we can observe, this is known as the "missing baryons" problem, and it is already taken into account when computing dark matter.

    Therefore, if the extra dwarf stars were to *double* our estimate for baryonic mass, all that does is resolve the missing baryons problem. And only if they triple or quatruple the baryonic mass estimate would then start moving into dark matter territory.
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  12. #9
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    Regarding these sneaky WIMP's, could relativistic jets be used as a tool
    to detect them?



    Regards

    Dustworm

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    Quote Originally Posted by Dustworm View Post
    What about a black hole, could it possibly catch and contain a much larger amount of WIMP's?

    Good question, I haven't thought about that before. Let me think... I'm not sure... On the one hand, once a WIMP crosses the event horizon, it can never get out. But on the other hand the event horizon is very small.


    Let's try a rough calculation first:

    The mass of the Sun is 2 x 10^30 kg. If it was a black hole, the event horizon would have a radius of 3 km. By comparison, the Sun has a radius of 700,000 km:

    R_Sun = 700,000 km
    R_BlackHole = 3 km

    The number of WIMPs that enter the star is roughly proportional to the cross sectional area of the star:

    WIMPs that enter the Sun = Some_Constant * R_Sun^2
    WIMPs that enter the BH = Some_Constant * R_BH^2

    Out of the ones that enter, for the Sun only 1 in about 10,000 get captured, while for the black hole 100% get captured:

    WIMPs captured by the Sun = Some_Constant * 1/10,000 * R_Sun^2
    WIMPs captured by the BH = Some_Constant * R_BH^2

    the ratio between these two quantities is:

    (1/10000 * R_Sun^2) / (R_BH^2) = 5.4 x 10^6


    So this calculation suggests that the Sun captures about 5 million times more WIMPs than if it was a black hole. This was just a rough calculation, but it gives us an idea of what's going on.

    A full calculation calculation would need to include gravitational deflection of WIMPs, but that's more tricky and I'd need to write a simulation for that. Gravitational deflection will change the answer in favour of the black hole, but probably by not more than a factor or 10 or at most 100.

    The other number that could be wrong is the 1/10,000 which I just guesstimated, but I suspect that if anything that number might be too low. I'm going to run a proper simulation to get the correct value, but I'm waiting for something else to compile first.

    Anyway, I think it's very safe to say that a black hole would capture fewer WIMPs than the corresponding star. Thanks for asking that question. It was something I hadn't thought about before.
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