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Thread: Thinking big!

  1. #1
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    Thinking big!

    This is fantasy, but I hope for some sensible comment from all you Cosmic Engineers out there.

    The Sombrero Galaxy is a spectacular sight, seen almost edge on, with a thick rim of dust. In fact a recent pic taken in the Infrared shows that almost all its dust is concentrated in the rim. http://apod.nasa.gov/apod/ap050511.html

    Could it be, could it just be, that this is the residue of a Galactic RingWorld?
    In Niven's stories, the Ringworld stays intact.
    In Iain M.Banks' "Consider Phlebas" he imagines a smaller version, an Orbital, that he then destroys, using the weapon 'grid-fire',a function of the energy between the universes in the Multiverse. I said this was fantasy!
    The fragments of the orbital are dust, that immediately spread out and disperse under radial momentum of the spinning Orbital.

    But a Galactic RingWorld is on such a different scale. How fast would it need to spin for One G at its inner surface? Not much, I suspect in relation to either the Orbital or RingWorld. So less radial momentum to spread it out, and the distances are galactic, not mere star-system, so it would take much, much longer to dissipate. In other words, could the Sombrero have been the site of a Galactic RingWorld, constructed out of all the dust that it originally contained, that has suffered a catastrophic disintegration?

    John

  2. #2
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    I suspect that there isn't enough baryonic matter in a galaxy to create such a ring. Just like there isn't enough matter in our solar system to build what most people would think of a ring world that surrounds our sun.

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    Also, sadly, unless it were made of materials that preserved the elemental abundances you would expect the shattered remains of such a structure to show up spectroscopically. There have been several spectroscopic studies of the galaxy and so far it looks like it is mostly hydrogen and simple species.

    If it is a galactic ring then the makers of it were a busy bunch (from Wikipedia):
    NGC 1291, a galaxy with an outer dust ring
    NGC 4725, a similar galaxy with an extended dust ring
    NGC 6027a, a member of Seyfert's Sextet with a very similar dust ring structure
    NGC 7742, a spiral galaxy with a similar dust ring

  4. #4
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    Spoilsports!

    Wayne,
    Not enough mass? The Sun weighs 2x10^30kgs and is about 98% of the mass of the Solar System.
    So the rest masses about 4x10^28kgs
    I am reliably informed that the RingWorld weighs 2x10^27kgs, so there IS enough mass to build a RingWolrd, by one order of magnitude!
    Of course, an accountant would build it thinner, to save money and mass!

    And, Shaula points out that Galactic RingWorld Engineers Inc. have visited several other galaxies, sadly without any more success than at the Sombrero.
    Clearly a design fault, rather than galactic warfare.
    They are building them too thin!
    Those bl**dy bean counters in charge instead of proper engineers, building robust, long-lived structures!
    You can't even buy a washing machine that lasts three years nowadays.
    Where do you go for a proper Galactic Ring?

    John

  5. #5
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    Quote Originally Posted by JohnD View Post

    But a Galactic RingWorld is on such a different scale. How fast would it need to spin for One G at its inner surface? Not much, I suspect in relation to either the Orbital or RingWorld. John
    Do you mean from centripetal force? In that case, the speed increases as the ring gets larger, so it would have to be phenomenally fast, no?
    As above, so below

  6. #6
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    Suppose our asteroid belt were to be hooked up with filaments by a spider, eventually it could form a ring, it is mostly in orbit already

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    Adding to my own question, the radius of the inside of the dust ring is about 15,000 light years. How fast would that have to spin to get 1g?
    As above, so below

  8. #8
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    Quote Originally Posted by Jens View Post
    Adding to my own question, the radius of the inside of the dust ring is about 15,000 light years. How fast would that have to spin to get 1g?
    If it's a torus with nothing in the centre that wiuld be v^2/R = 10 m/s/s
    so keeping to round numbers say 10^16 m for a light year v^2 = 10^17 so v is about 3. 10^8 m/s

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    a = v^2 / r for centripetal/fugal accelerations. So in this case V = sqrt (ar ) = sqrt( 9.5e15 * 15,000 * 9.8 ) = 3.7e10 m/s. Ooops. We have lightspeed issues.

    w = sqrt( a/r ) so w = 2.6e-10 or one revolution every 6e8s or about 20y. Yeah, 20 year orbital period at 15K ly... That is not going to be easy! Maybe that is why they are all dust rings now. Spin up didn't go so good.

  10. #10
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    Quote Originally Posted by Shaula View Post
    a = v^2 / r for centripetal/fugal accelerations. So in this case V = sqrt (ar ) = sqrt( 9.5e15 * 15,000 * 9.8 ) = 3.7e10 m/s. Ooops. We have lightspeed issues.

    w = sqrt( a/r ) so w = 2.6e-10 or one revolution every 6e8s or about 20y. Yeah, 20 year orbital period at 15K ly... That is not going to be easy! Maybe that is why they are all dust rings now. Spin up didn't go so good.
    sorry to be dim but what is the 15000? oops I missed the 15000 reading too fast, thought it was one light year sorry!
    Last edited by profloater; 2013-Jul-16 at 02:34 PM. Reason: found my mistake

  11. #11
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    Quote Originally Posted by profloater View Post
    sorry to be dim but what is the 15000? oops I missed the 15000 reading too fast, thought it was one light year sorry!
    15000? For what appears to be a good sized spiral? Way too small?

    Regards, John M.
    I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.

    "Mainstream isnít a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik

  12. #12
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    I found 25,000 somewhere, but it doesn't matter because that would just make the problem worse.

    Maybe it was made of tachyons.
    As above, so below

  13. #13
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    Quote Originally Posted by JohnD View Post
    Spoilsports!

    Wayne,
    Not enough mass? The Sun weighs 2x10^30kgs and is about 98% of the mass of the Solar System.
    So the rest masses about 4x10^28kgs
    I am reliably informed that the RingWorld weighs 2x10^27kgs, so there IS enough mass to build a RingWolrd, by one order of magnitude!
    Of course, an accountant would build it thinner, to save money and mass!

    And, Shaula points out that Galactic RingWorld Engineers Inc. have visited several other galaxies, sadly without any more success than at the Sombrero.
    Clearly a design fault, rather than galactic warfare.
    They are building them too thin!
    Those bl**dy bean counters in charge instead of proper engineers, building robust, long-lived structures!
    You can't even buy a washing machine that lasts three years nowadays.
    Where do you go for a proper Galactic Ring?

    John
    where did you get your estimation for the mass of a ring world?

  14. #14
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    Quote Originally Posted by JohnD View Post
    Spoilsports!

    Where do you go for a proper Galactic Ring?
    I think you might find instructions in how to build one in a shop called Flourish & Blotts.
    As above, so below

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    I'm curious.... How fast would a ringworld @ one AU from Sol have to spin to create one G? Hmmm... thats got to be easy

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    Quote Originally Posted by Grant Hatch View Post
    I'm curious.... How fast would a ringworld @ one AU from Sol have to spin to create one G? Hmmm... thats got to be easy
    the formula as above is just v^2/r = accn. = g
    however I prefer the asteroid belt as a starting point

  17. #17
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    So, after we tie them all together with spider webs, how fast do we need to accelerate the asteroid belt to produce 1 G? How much tension would this put on the webbing?

  18. #18
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    OK here's a plan, the asteroid belt is about 3 .10^21 kg, quite small really and we could start with a base on Ceres, the biggest, at around 4.10^8 km radius. With a robotic grab hook we start to rope in minor asteroids in one direction and with just that little reactive push we alter ceres orbit to grab others, at the same time we extend a long rope about 10^9 km long to form the hoop and we catch it as it completes. That might take at 1 km/s 100 years. Something for the grandchildren. Then a special craft using the hoop sets off to tie in the larger lumps. That might take say, 10,000 years, you have the think big, and this is just a solar scheme. Now as for the question, if you accelerate the orbit tries to get bigger but the hoop resists that. At 1 g the force is, I think 3.10^22 N. But during the million years it might take to do that we might work out what to use for the hoop, given that we will have at least a couple of aeons and the advent of superior intelligence by then, and still they might ask, why? Well from Earth it would be very pretty lit up at night with advertising.

  19. #19
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    The thread has drifted a bit, but since we're here, how much energy would it take to stabilize it? One poster used the term "orbit" but a ring is not in orbit and will will not remain stable unless you actively stabilize it, right?
    As above, so below

  20. #20
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    Quote Originally Posted by Jens View Post
    The thread has drifted a bit, but since we're here, how much energy would it take to stabilize it? One poster used the term "orbit" but a ring is not in orbit and will will not remain stable unless you actively stabilize it, right?
    Far less energy than it would take to map the bodies and hop between them to get to where we want to go and avoid being on the ones that are about to collide.

  21. #21
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    Your thread is near the 30 day limit. It was a fun thread, unusual for ATM. You're a good sport.

    Regards, John M.
    I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.

    "Mainstream isnít a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik

  22. #22
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    And with that I close the thread.
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