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Featured B First Interstellar Asteroid Found

  1. Nov 24, 2017 #81

    DaveC426913

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    Interesting. But it would be a fine balance.Enough force to deform it - even over a long timespan - would be very nearly enough to fling anything not nailed down off into space.
    They said they detected zero coma, which is what ruled it out as a comet. But it would also put an upper limit on the amount of dust and grains that would be surrounding it, if such dust and grains were to be flung off by spin.
     
  2. Nov 25, 2017 #82

    OmCheeto

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    From the site I checked for "meteor density", their range was 1790 thru 8000 kg/m3. The most common being 3400 kg/m3. So even their lightest meteor density would yield a tip gravity that exceeds centripetal force by 60%. Which kind of implies that nothing should ever get flung off by its spin, at least recently.

    Perhaps tomorrow I'll spin the creature back down to a spheroid, a billion years younger, and see how the maths works out.

    I also wonder if anyone would know how to model a full metal asteroid of this size. Say, create a 40 meter diameter, 400 meter long nickel-iron cylinder, support it on one end, and see how far it droops over time. Metallurgy is one of my least studied subjects.
    Plasticity, looks like it might be a good candidate, though even the wiki description makes my head hurt. I put the odds at 1000:1 against me being able to get anything useful out of that.

    That's interesting that no coma was seen. Thinking about it though, it kind of makes sense. Something traveling between stars or galaxies wouldn't have the swarm of dust and stuff you find spinning lazily around a solar system. I'm guessing most everything it met was going 94,000 kph! (60,000 mph)

    More things for me to think about in the morning: Interstellar and intergalactic hydrogen densities.

    Lot's of interesting stuff to think about!
     
  3. Nov 25, 2017 #83

    stefan r

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    No, would be 0 stress. An elongated non-rotating asteroid would have more compressive stress at the center. Force from rotation would have to exceed gravity in order to cause tensile stress.

    You might be thinking of cyclical stress. If you bend a bar back and forth it can harden and become more brittle. The material in the asteroid should not be bending at all. Especially in interstellar space were there is nothing (very little?) to give it tidal forces.

    It would have billions of years (or insert age) of ionizing radiation. Asteroids in our belt would have same/similar cosmic radiation and a lot more solar wind. "More brittle" does not mean the same thing as "weaker" and sometimes the opposite. We use ion implantation to toughen steel drill bits.
     
  4. Nov 25, 2017 #84

    OmCheeto

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    Ouch! I do believe you are correct. I'll have to spin this thing backwards in time to see what happens.

    Like I said, metallurgy and rocks are two of my weakest points. Where are @davenn & @billiards when you need them.
    What the heck could shape a rock like that in outer space? Or did it start that way, like some giant splinter?
     
  5. Nov 25, 2017 #85
  6. Nov 26, 2017 #86

    OmCheeto

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    Yes, I saw that. It's kind of big to be a "splinter", so that would be my last choice as to why it's shaped like it is.

    But I did finish my retro spin analysis. All I can say is that the universe gave us a great homework problem.

    2017.11.26.Oumuamua.spin.analysis.png
    When centripetal acceleration is greater than gravity(at the ends), then there will be a tensile stress.

    Bumping the density up to that of dwarf planet Haumea, bumps the "g" curve up, yielding a less elongated equilibrium length to diameter ratio:

    2017.11.26.Oumuamua.with.Haumeas.average.density.png
    Looks like 6.5:1 to me.

    One can only scratch one's head about the evolution of such graphs.
    Did Oumuamua partially evaporate on its journey?

    Further reading: Jacobi ellipsoid
     
  7. Nov 26, 2017 #87

    sophiecentaur

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    We're all stationary, relative to ourselves but what reference frame did you assume for the visitor?
     
  8. Nov 26, 2017 #88

    DaveC426913

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    I believe NR is saying,
    - never mind whether or not the object is moving or stationary wrt any other FoR.
    - Is it possible the object is not gravitationally bound to either our system or another nearby system.

    I'd have to track it down, but yes, there was a hypothesis that the object could have formed independently of a star system, such as perhaps part of a rogue planet.
     
  9. Nov 27, 2017 #89

    sophiecentaur

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    If it is stationary relative to our Solar Sysyem, it won't be approaching us so we would never observe it going through the SS. It would not surprise me to find objects like that, in deep space, that have been 'tracking us' for millions of years but that's not what the thread has been discussing.
    The train and the fly are heading towards each other and the same damage still be done at the collision, whatever FoR we use. I don't think that 'stationary visitor' is a meaningful description.
     
  10. Nov 27, 2017 #90

    tony873004

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    I made a new simulation where you can pan around. It's similar to the one I already posted, except it includes a path for Oumuamua. The previous one didn't because the code only knew how to superimpose Keplerian ellipses, not hyperbolas. So I had to hand-code Oumuamua's path.
    http://orbitsimulator.com/gravitySim.../oumuamua.html
     
  11. Nov 27, 2017 #91
    A minor note: Wikipedia is incorrect - surprise, surprise! - about Haumea's density.

    It is actually about 1.9 grams per cubic centimeter, nearly the same as Pluto's. See Ken Croswell and Nature.
     
  12. Nov 27, 2017 #92

    OmCheeto

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    Oops!
    I should have checked further.

    wiki, regarding Haumea's density, in the side-bar:
    Mean density
    2.6 g/cm3[9][13]
    1.885–1.757 g/cm3[8]

    My bad.
     
  13. Nov 27, 2017 #93

    OmCheeto

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    ps. Any spiritual Ferengis, in the future, who should spot an extrastellaroid, with a 2:1 ratio, should shell out the money to catch it.

    2017.11.27.L.vs.D.ratio.extrastellar.object.value.png



    kg/m^3 Name
    18,950 Uranium
    19,320 Gold
    19,350 Tungsten
    19,840 Plutonium
    20,200 Neptunium
    21,040 Rhenium
    21,450 Platinum
    22,400 Iridium
    22,600 Osmium

    pps. You do the maths...... (≈7 billion kg of gold plated latinum!)
     
  14. Nov 27, 2017 #94

    DaveC426913

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    Agree. The point is that its motion is a red herring to NR's argument (as I see it). It just confuses the issue of what he's trying to ask, which is about being bound to some star.
    The object is not g-bound to Sol; is it possible it's not (and never was) g-bound to any other star system?
    (Of course, it is g-bound to the Milky Way)
     
  15. Nov 27, 2017 #95
    Finding an intergalactic asteroid really would be very impressive.
     
  16. Nov 28, 2017 #96
    Presumably they are much more numerous than their interstellar cousins, considering galactic evolution is orders of magnitude more chaotic than mere stellar dynamics.
     
  17. Nov 28, 2017 #97

    stefan r

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    Why are we presuming that? For an asteroid to escape the milky way from the solar system it would need to gain several hundred km/sec.

    Is there any reason to believe population 2 or population 3 stars form a lot of asteroids?
     
  18. Nov 29, 2017 #98
    We see numerous examples of galactic mergers or large galaxies sucking material from their companions (M51 and NGC 5195 eg). I'm assuming these processes result in the transfer of quadrillions of asteroids, comets and other debris.
     
  19. Nov 29, 2017 #99

    OmCheeto

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    Ehr mehr gerd.......
    This is so much fun.

    Given the wiki-posted range of interstellar Hydrogen density, and the possible time range this object has been traveling, I come up with a range of energies colliding with interstellar hydrogen of:
    1. enough to cook a piece of toast, 0.03 kwh (given the minimums of 250,000 years & 0.4 mg of Hydrogen), to
    2. 16 trillion kwh (13 billion years & 190 billion kg of Hydrogen)​
     
  20. Nov 30, 2017 #100
    Look at the stars. Extragalactic stars exist, but are less common than stars in galaxies.
     
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