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Theoretical scenario for star-forming need help with a calculation!

  1. Jun 22, 2011 #1
    Theoretical situation:

    Temperatures at a point near the center of a gas giant of another star system have been artificially raised by local ET intelligence in order to achieve the heat to begin the fusion process. The planet has enough internal pressure to sustain the fusion process and it has the right ingredients, so it now has the three ingredients to form a star from a gaseous planet, roughly the composition and size of one Jupiter mass, even though the starting FUSION temps have been created artificially.

    My questions are: How long would it take for this small, artificially-induced star to manifest obvious visual evidence at its surface? Would we see heat convection rise up from the center within a matter of years? Would we see lightning flashes at the surface? What would we see and initial and on-going visual evidence? How soon would we see a change in VOLUME of the body?

    Since this star is artificial, how would it act differently from a normal process star?

    The sun's fusion reactions take many thousand of years to arrive at the surface, but the sun is generally in equilibrium, whereas our theoretical star is NOT in temperature equilibrium.

    Thanks!

    JC
     
  2. jcsd
  3. Jun 22, 2011 #2

    Drakkith

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    How would the planet have enough internal pressure without all the mass of a normal star?
     
  4. Jun 22, 2011 #3
    The internal pressure you talk of is that required to raise the TEMPERATURE TO START fusion spontaneously. We are assuming this rule has been bypassed because the TEMPERATURE SPARK has been supplied artificially with outside technology. It's a theoretical situation. Assume the pressure to SUSTAIN fusion is available.
     
  5. Jun 22, 2011 #4

    Drakkith

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    No I mean to sustain the reactions. If you quit heating it, the temperature cools down and fusion stops. Without sufficient pressure to contain the plasma, it expands until fusion ceases.
     
  6. Jun 23, 2011 #5
    There is sufficient pressure. To sustain fusion, to contain the nuclei, etc., it only takes about 3 million bars, assume we have 30 million bars of pressure at the point where the fusion temp. spark was initiated. Assume we are near the center of the planet at 30 million bars of pressure.

    3 things are required for sustained fusion:
    Correct ingredients (assume we have the right hydrogen and helium)
    Correct pressure (assume we have 30 million bars)
    Correct starting temperature (this is what the massive mass is said to be for, the STARTING temperature)
    -once fusion is started, the temperature is self-fulfilling from that point on, it's several orders of magnitude greater than what is required to START the process. Assume we have ARTIFICIALLY provided the starting temperature.

    Total liberated energy is 1000 to 2000 times more than energy required to start fusion (D-T).
    Some D-T can start as low as 12 million K, but average is 120 million K (.01 MeV). But it liberates several orders higher than this in energy (17.6 MeV).
     
    Last edited: Jun 23, 2011
  7. Jun 24, 2011 #6
    Neither D-T or D-D fusion can be stable except at low concentrations. Both would undergo runaway fusion and the whole mass would disrupt, below a critical level - the exact value of which I am unsure. Stars only have a Main Sequence because proton-proton reactions are low probability and the half-life of the reactants is ~8 billion years in stellar core conditions.
     
  8. Jun 24, 2011 #7

    Drakkith

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    I haven't ran the numbers, but IF the pressure is enough to sustain the reaction, then I would guess that we would see the results relatively quickly.
     
  9. Jun 24, 2011 #8
    Minimum for sustained D-D fusion in brown dwarfs is about 2 billion bars and about 500,000 K temperature. And there's just no way to get that much D-T together - tritium is too hot! It's energy production rate of 325 W/kg is much higher than the core of the Sun, let alone a brown dwarf. A mere planet can't contain a sustained fusion reaction by gravitational pressure.
     
  10. Jun 24, 2011 #9
    http://iopscience.iop.org/0741-3335/48/5/B01
    Fusion, the Energy of the Universe, McCracken
    Figure 4.9, pg. 45

    Fusion in a reactor:
    Pressure=30,000,000 bars
    Confinement time=1/6,000,000 seconds
    Temp=100 to 200 million C

    This is on the Inertial Confinement side for "Ignition Criterion".

    Also see: http://en.wikipedia.org/wiki/Nuclear_fusion
    for D-D some fusion reactions start as low as 25 million K, x10 for the average, so 250 million K.
     
    Last edited: Jun 24, 2011
  11. Jun 24, 2011 #10
    When you say relatively quickly, are you imagining a few months, or a few years....?

    What would we see first as evidence at the surface, what would we see next?....any guesses?

    Thanks for your responses!
     
  12. Jun 24, 2011 #11

    Drakkith

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    I'm guessing somewhere on the order of days, as the density and size of the planet is MUCH less than a star. Just be aware that this is highly speculative as I don't believe it is possible for a planet to sustain fusion by gravitational confinement. I don't think the numbers from our reactors here on earth are accurate for what goes on in the core of a star. Assuming that there is sufficient Deuterium to sustain a reaction it would be burned off very quickly.
     
  13. Jun 24, 2011 #12
    If you read your source a bit closer you would've noticed that the temperature x density gives the pressure of the plasma, and that the product of the plasma pressure and the energy confinement time must be great than 5 to achieve ignition. A giant planet's core has a density of ~30,000 kg/m3, so a temperature of ~200 million K means a confinement pressure of ~1 trillion bars to hold a plasma of that density at that temperature. Else it will expand vigorously until the plasma cools sufficient to achieve a new equilibrium.

    The relationship between pressure, density and temperature is what the standard gas laws tell us, but with the average particle mass reduced because of the tiny mass of electrons in an ionized plasma.

    Thus: P = ρ.RT/μ ,where μ ~0.5 g/mol, due to the electrons.

    ...fusion reaction rates increase with the square of the density. Imagine the fusion core of the hypothetical planet as a sphere of high density plasma. It's density declines with the inverse cube of the radius, R, so the reaction rate declines with the inverse ~1/R6. In fact it's worse than that because the temperature also declines with the square of the radius in an expanding sphere, meaning the fusion rate declines (roughly) with the ~1/R12, assuming a linear reaction-rate dependence on temperature (which is roughly true for small perturbations.) Expand the fusion core by 2-fold, drops the reaction rate by 4,096. I would suggest that means an increase in temperature/pressure from fusion would be very rapidly quenched. Such cyclical perturbations from equilibrium would travel outward as pressure waves, which would be noticed at the surface in hours, at most.

    Perturbations from fusion equilibrium cause Cepheid variables to change their luminosity in a periodic fashion, quite rapidly considering the immense size of such old, evolved stars. I imagine the changes would be noticed at the surface of a mere planet very rapidly indeed.

    Finally, deuterium burning in brown dwarfs proceeds very slowly, largely due to the fuel being a small fraction (~0.015%) of the core material. Over about 50 million years the deuterium declines by about 90% then becomes too low for the fusion to continue.
     
  14. Jun 24, 2011 #13

    Chronos

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    Sustained fusion in a sub-critical mass planet could not be achieved without significant engineering enhancements. Artificial fusion requires precisely controlled plasma density and a way to remove ash from the process. If the plasma density drops too low, the reaction ceases. If it gets too high you get runaway fusion [e.g., thermonuclear bomb]. ET would have to engineer something to regulate the plasma density snf purity. In a nomal star, gravity and convection work together to naturally regulate plasma density and purity. If something gets out of whack, a star self adjusts by expanding or contracting. All stars are variable to some extent for this reason. Fortunately, our sun only varies by a fraction of a percent - for now.
     
    Last edited: Jun 25, 2011
  15. Jun 24, 2011 #14
    Thanks all for your responses, good information!
     
  16. Jun 24, 2011 #15
    Let's say that we have a megajovian near the edge of a globular cluster containing many microquasars. Let's say the cluster is part of a dwarf galaxy that is flying past merging, giant, elliptical galaxies within a supercluster. Additionally, the galaxies are merging at an acute angle in such a fashion that their quasars/AGNs converge at a particular point.

    Let's say that everything is pretty optimally placed. I'm guessing that even a megajovian would be stripped of gas if it were to slowly pass through all those things, so let's say that everything optimally turns on all at once and as fast as possible. Additionally, let's say that extremely massive stars are optimally placed to focus some of the energy of most of those energetic systems.

    I suppose that everything would depend on the composition of the material flowing into the systems/from the particle jets and the distance to the relevant objects, amongst other factors. Lastly, it would also depend on the star cluster, dwarf galaxy, interstellar and intergalactic medium. I don't really know the optimal combination of factors that would lead to the most extreme burst of continuous energy. Under the craziest, logically conceivable conditions, are there any exciting events that might transpire?
     
  17. Jun 24, 2011 #16

    Drakkith

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    Nick, what exactly are you asking? You've typed up a crazy post that I can barely wrap my head around thanks to all these "assumptions".
     
  18. Jun 25, 2011 #17

    Chronos

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    Attempts at artificial fusion rely on powerful magnetic containment fields as a substitute for enormous graviy. Plasma is hot and requires extreme force to contain it while avoiding incinerating everything else required to sustain fusion. We have not yet mastered thls technology.
     
  19. Jun 25, 2011 #18

    It was Friday night. My fiance bombarding me with questions while covering me with the condensation from her wine bottle. Not only was I highly distracted, but I also wanted to post something as quickly as possible to stop the madness.

    Additionally, it was very convoluted because I was trying to outline a slightly plausible scenario where something like that might take place. And, I wanted to acknowledge that a number of deterministic factors, such as the medium between the energy sources, their distances, the inflowing matter, mass/composition of each object, the rate at which the transfer of energy intensifies, etc., would need to be considered. Honestly, I just wanted to give as much wiggle room as possible while also deflecting simple questions designed to avoid providing an answer.​



    1. If something close to the mass of a failed star were simultaneously, and somewhat optimally(e.g. everything hits it all at once, like spotlights on a stage), blasted by several microquasars and the jets of two quasars, could anything exciting transpire?
    2. If some behemoth, gravitational lenses(e.g. an ejected SMBH and a hypergiant or an intermediate blackhole) were in between the super-jupiter and the quasars, could that positively affect the chances of an exciting effect occurring?

    The thread made me wonder if that type of scenario might cause some sort of short-lived, natural phenomena. My guess is that, even in the best-case scenario, it might just strip off the gas and that most of the energy would uneventfully radiate away. I don't even know how much energy could be transferred, nor how those gravitational lenses would alter a relativistic jet.

    It seems like the gravitational lenses could increase the total amount of energy transferred, concentrate the energy, diminish the total amount of energy that would have otherwise been transferred by the active galactic nuclei or mostly just alter trajectory and velocity of the particles passing by the objects(e.g. reduce the quantity reaching the exoplanet). I'm sure that part of it would depend on whether focal point is on, slightly in front of or slightly behind the center of the super-jupiter.

    EDIT: Let's also make the "assumption" that the planet doesn't have an orbit around a star because of some sort of gravitational interaction that previously took place within the globular cluster/dwarf galaxy.
     
    Last edited: Jun 25, 2011
  20. Jul 6, 2011 #19
    A side note to this question:

    IF such a ball of fusion could be created artificially inside a gas giant, would it, by default, have a density less than the atmosphere above it (or liquid hydrogen above it) and therefore try to "float to the top", or would it create "simulated density" because it had equalized with the pressure of the zone it is in.

    In other words, would it, as a ball of fusion, although less dense from expanding, actual be simulating a greater density from its fusion pressure?
     
  21. Jul 7, 2011 #20
    Taking the sun, for example:
    central density 160 g/cm-3
    central temp 15,000,000 K

    qraal, according to your numbers, the sun would not be able to hold its central fusion. It would need 400 billion bars of pressure, and the estimate for its center is 100 - 250 billion bars. I may have some calc. wrong here though. Could you give me a play by play?

    Also, the unexplained temp. rise near the surface of the sun does not make sense.

    There is also an unexplained temperature DROP near the center of the sun according to this model:

    http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/SunLayers.html

    If the inverse properties hold true for temperature at the center of the sun, it should be over 18 million K there and not 15 million.
     
    Last edited: Jul 7, 2011
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