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Thread: Iron sequestration helpful?

  1. #1
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    Iron sequestration helpful?

    At the recent ALCON event, someone asked how Nature benefited from blackholes? Teleological questions can be quite interesting, and this looks like a dandy. One thought I considered was that iron would be less invasive to new stars. Does this benefit evolution by giving it more starshine time, or not? Or is there some other benefit? Perhaps galaxies could not form without them. Perhaps future galactic travel will require them, or something.

    What should Mother Nature say about their efficacy?
    We know time flies, we just can't see its wings.

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    Another way to ask...

    Does increased metalicity, specifically iron, decrease stellar life? Perhaps the question depends on the amount of iron in a nascent star where a little helps but too much causes problems?
    We know time flies, we just can't see its wings.

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    In general, the smallest mass at which fusion will occur decreases with increasing metallicity. That is, a pure hydrogen object must be XX solar masses in order to cause fusion in the core, but an object with a significant amount of metals can be much less than XX solar masses.

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    Nature "benefits" from gravity, of which black holes are a side effect. Can't have one without the other.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by StupendousMan View Post
    In general, the smallest mass at which fusion will occur decreases with increasing metallicity. That is, a pure hydrogen object must be XX solar masses in order to cause fusion in the core, but an object with a significant amount of metals can be much less than XX solar masses.
    Would this mean that all stars would burn faster, and die quicker, as a result? If all the iron that collapses during the black hole formation were instead foisted into protostellar nebulae, would metalicity be so high to do more harm than good. I suppose we need to make some assumptions on what is "good", perhaps evolutionary timesacales of several billion years under a steady-Eddie star might be one to consider.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    Would this mean that all stars would burn faster, and die quicker, as a result?
    This article has a good discussion of stars and increasing metallicity:

    A DYING UNIVERSE: The Long Term Fate and Evolution of Astrophysical Objects

    http://arxiv.org/pdf/astro-ph/9701131v1.pdf

    For small stars, they calculated a "sweet spot" for metallicity. Up to the sweet spot, increases in metallicity allows an increase in the hydrogen burning phase. Above the sweet spot, the decrease in total available hydrogen decreases the hydrogen burning phase, even though the star would use hydrogen more frugally. They refer to the maximum lifetime stars as "frozen stars" because the temperature at the top of the atmosphere would stay roughly at the freezing point for water. However, these stars would have a very long lifetime - they claim something on the order of a thousand times longer than today's low mass stars which themselves are expected to stay on the main sequence for around a trillion years.

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    Quote Originally Posted by Van Rijn View Post
    This article has a good discussion of stars and increasing metallicity:

    A DYING UNIVERSE: The Long Term Fate and Evolution of Astrophysical Objects

    http://arxiv.org/pdf/astro-ph/9701131v1.pdf
    Very nice and interesting!

    Their luminosity equation involving mass and mean molecular weight (bottom of pg. 6) is especially intriguing. Luminosity increases as the 7.5 power of mean mol. wt. So, what if all those metals that would have been lost to a black hole were spewed in SN explosions and we simply double (arbitrarily) the mean mol. wt. The star life, from the eq. 2.3 decreases 180x, so that our star in this example would be at today's evolutionary point in only about 28 million years. Darwin wouldn't like it and he called Lord Kelvin and "odious spectre" for using a similar too short a period for the age of the Earth.

    Perhaps doubling the mean mol. wt. is way too extreme. We should be able to calculate it, given a little free time, which I rarely have these days.

    ...They refer to the maximum lifetime stars as "frozen stars" because the temperature at the top of the atmosphere would stay roughly at the freezing point for water.
    Herschel would have loved this one. He suggested that beings might life under the surface of the Sun. Double crazy idea given what we now know, yet for these stars, these beings might have to!
    We know time flies, we just can't see its wings.

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    Frozen stars, eh? This sort of object can't exist in our current era, or would be very rare. But they would be worth colonising once they do exist, since they will continue to shine at near-Earth temperatures for a quadrillion years. Perhaps it would be worthwhile trying to manufacture them.
    Last edited by eburacum45; 2014-Jul-26 at 10:03 AM.

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    I seem to remember a novel "star king" featuring something similar...

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    Quote Originally Posted by George View Post
    Herschel would have loved this one. He suggested that beings might life under the surface of the Sun. Double crazy idea given what we now know, yet for these stars, these beings might have to!
    For those us (me) who are only semi-educated, what type of surface gravity would a low mass "frozen star" have?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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