1. Subscribersonhouse
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    28 Aug '13 15:21
    http://phys.org/news/2013-08-oldest-solar-twin-vlt-clues.html
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    28 Aug '13 17:075 edits
    Strangle, the link doesn't explain exactly in what way this star is very much “like” Sol.

    Anyone:

    Do they simply mean (by “like” ) it has almost exactly the same mass as Sol? If so, then their assumption that it could show us what Sol would be like 4 billions years time is deeply flawed because Sol would loose a large proportion of that mass by the time it becomes as old as that other older star is now and thus would NOT ever be like that star! And that other older star would have been a lot more massive when it was the age Sol is now! And so that other star would NEVER been like Sol!

    OK, if they don't mean it is like Sol specifically in terms of mass, then in what way like Sol?
    Do they mean that they have calculated that its mass would have been almost exactly that of Sol when it was the age Sol is now? if so, wouldn't that mean that they are making assumptions about the rate of loss of its mass as it evolved within the last 4 billion years which may not necessarily be totally accurate or reliable? -this would be my main concern.
  3. Standard memberDeepThought
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    28 Aug '13 18:47
    Originally posted by humy
    Strangle, the link doesn't explain exactly in what way this star is very much “like” Sol.

    Anyone:

    Do they simply mean (by “like” ) it has almost exactly the same mass as Sol? If so, then their assumption that it could show us what Sol would be like 4 billions years time is deeply flawed because Sol would loose a large proportion of that mass by the ...[text shortened]... rs which may not necessarily be totally accurate or reliable? -this would be my main concern.
    I think they mean it's got the same classification G2V, which constrains the mass fairly tightly. It's still in the main sequence, so it's properties won't have changed that much, although it's power output will be higher than earlier in it's lifetime. From memory, the losses from solar wind for dwarf stars aren't that intense until they stop being dwarfs. According to the Wikipedia page on Solar Wind the sun's so far lost about 0.01% of its mass, so it's unlikely this other star will be much different.

    The interesting result is that the amount of lithium decreases while the star is in the main sequence. The reaction Li(7, 3) + p ---> Be(8, 4) ---> 2 He(4,2) is part of the proton-proton chain and occurs in the sun, but most of the lithium in a star is consumed in the proto-star phase. It could easily have been that the percentage of lithium is stable during the main sequence and that the sun is just anomalous. Their result is useful because it means that the amount of lithium in the star gives you information about how old it is.
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    28 Aug '13 20:45
    Originally posted by DeepThought
    I think they mean it's got the same classification G2V, which constrains the mass fairly tightly. It's still in the main sequence, so it's properties won't have changed that much, although it's power output will be higher than earlier in it's lifetime. From memory, the losses from solar wind for dwarf stars aren't that intense until they ...[text shortened]... means that the amount of lithium in the star gives you information about how old it is.
    According to the Wikipedia page on Solar Wind the sun's so far lost about 0.01% of its mass

    Yes, I just checked this and you are right. My memory completely failed me here because I thought I remembered reading somewhere that it lost a lot more than that!
    Must have somehow got that mixed up with the substantial mass it would loose when it turns into a red giant!

    Just thought of another possible flaw in the reasoning; How do they know that this older star had the chemical elements in almost exactly the same proportions as Sol did when it was the age Sol is now? Because, if my memory serves me correctly (this time ), the gas clouds that collapse to make stars vary considerably in their proportions of chemical elements with some having a much larger proportion of hydrogen and other lighter chemical elements compared to the heavier chemical elements and others having a much smaller proportion.
  5. Subscribersonhouse
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    28 Aug '13 21:41
    Originally posted by DeepThought
    I think they mean it's got the same classification G2V, which constrains the mass fairly tightly. It's still in the main sequence, so it's properties won't have changed that much, although it's power output will be higher than earlier in it's lifetime. From memory, the losses from solar wind for dwarf stars aren't that intense until they ...[text shortened]... means that the amount of lithium in the star gives you information about how old it is.
    Wow, that means for people living there, lithium ion batteries are going to be WAY more expensive than here on Earth! So lets form a trade union and go there and sell them lithium!
  6. Standard memberDeepThought
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    28 Aug '13 22:18
    Originally posted by humy
    According to the Wikipedia page on Solar Wind the sun's so far lost about 0.01% of its mass

    Yes, I just checked this and you are right. My memory completely failed me here because I thought I remembered reading somewhere that it lost a lot more than that!
    Must have somehow got that mixed up with the substantial mass it would loose when i ...[text shortened]... elements compared to the heavier chemical elements and others having a much smaller proportion.
    I had a look at the paper (they get the wrong end of the stick every now and again but phy.org get credit off me for making the basic research easy to find) which is here: http://www.eso.org/public/archives/releases/sciencepapers/eso1337/eso1337a.pdf and they're basis for the claim about composition seems to be based on previous work. I've only read the introduction and I'm off field, so... Although their primary interest seems to have been lithium, if I've read it right they measured the other metals as well. They'll be looking at spectroscopic line brightness (not in the intro), but further than that this is beyond my ken. They're helped a lot by the proximity of this star - for example at a mere 250 light years its distance will be known from parallax measurements which are quite accurate.
  7. Standard memberDeepThought
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    28 Aug '13 22:27
    Originally posted by sonhouse
    Wow, that means for people living there, lithium ion batteries are going to be WAY more expensive than here on Earth! So lets form a trade union and go there and sell them lithium!
    The amount of lithium in the Earth is not related to the amount of lithium in the Sun. For a terrestrial planet around that star the percentage composition will depend on the collapsing nebula's composition - not the amount of lithium in the star, since that all gets burnt in the proto-star stage.

    Besides with a round trip of at least 500 years you won't get much investor interest.
  8. Subscribersonhouse
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    29 Aug '13 02:548 edits
    Originally posted by DeepThought
    The amount of lithium in the Earth is not related to the amount of lithium in the Sun. For a terrestrial planet around that star the percentage composition will depend on the collapsing nebula's composition - not the amount of lithium in the star, since that all gets burnt in the proto-star stage.

    Besides with a round trip of at least 500 years you won't get much investor interest.
    Bust my party will you🙂

    As to the composition, I read an article in Scientific American a couple years ago about the stars that formed together with Sol from the same cloud, I recall there being something like 1500 to 5000 stars coming from that cloud and all resulting in more or less G2's. They then traced where they are today and they are spread out in our local arm around 1000 LY apart in more or less a straight line, kind of bunched together in a long string. Not sure whether this star under study was in that group. It sure sounds like it though.
    It would be an extremely fascinating trip if we can ever achieve interstellar travel.

    200 LY's puts it really close in the big picture.

    A generation ship going 0.1c would take 2000 years one way with no appreciable relativistic effects. I suppose a trip like that could be planned where everyone is cryogenically frozen or you have frozen embryo's decanted say 25 years just before arrival and robots bring up the kids with lots of recordings of images and voices from Earth. Lots of ethical concerns there!

    At 0.9c I think you get effective times for those onboard of about 2.3c so that would be about 86 years ship time.

    At 0.99c it would effectively be about 7c or 28 years ship time. Of course round trip leaving today would still get you home in the year 2500 or so depending on how much time you sped there and how much time it takes to get to 0.99c. If you could manage 0.999c that would be about 22c ship time so that would be a trip of about 9 years, starting to get reasonable. 20 odd years round trip. You still don't get back till the year 2400 minimum though.

    It gets more serious at 0.9999c, about 70c so about 6 years round trip time which helps those on board but doesn't help Earth much, you still take 400 years round trip, Earth time.

    So 5 9's c gets you to about 223c so ship time of less than a year, couple years there and back. Still puts you back at the year 2400 or so, no help for that. You would need some serious propulsion though, at least 1 g constant accel. Gets you close to c in about 1 year.

    Would not want to run into a meteor at that speed though🙂 There would clearly be associated with such a ship heavy duty shields, magnetic, laser blasters (mainly to ionize stuff ahead of you so the magnetic shield would deflect it)

    My guess is such a craft would be shaped like a loop, like a bracelet where the magnetic lines of force would converge inside the loop to direct ionized bad stuff and radiation looping around the lines of force.

    It would be a real boon if we ever got the drives envisioned by the Nasa propulsion dudes though, the space warp drive where space would be curved positive in back and negative in front and you would be kind of like going downhill all the time achieving an effective faster than light speed but without the relativistic effects, so if you were going 10c it would take 20 years to get there and 20 years back and 40 years would go by on Earth so you would be in sync timewise, your brother would be the same age as you when you got back and so forth. That would be barely in the realm of possible, leave at the age of 20 and get back at the age of 60 or 65 or so. It would certainly be your life's work.

    It would be fascinating to see an Earth like planet there 4 billion years further on than Earth, if there ever was some kind of scientific civilization there and long gone you might not EVER find evidence if there was anything like the geological activity of Earth. Of course if OUR sun was still something like what it is now, 4 billion years from now might run our core down in temperature where continental plates get fixed in place and no more major crunching taking place. Our moon would be long gone, joining the crowd in stellar space, maybe crashing into Jupiter or something but for sure not close to Earth any more, gravitational instabilities would see to that. So not much in the way of tides. Sounds like a boring planet...

    On the other hand if things go like Kurzweil thinks there could be some kind of immortal life there still. Wonder what they would think of Earthlings.
  9. Cape Town
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    29 Aug '13 06:22
    Originally posted by sonhouse
    A generation ship going 0.1c would take 2000 years one way with no appreciable relativistic effects. I suppose a trip like that could be planned where everyone is cryogenically frozen or you have frozen embryo's decanted say 25 years just before arrival and robots bring up the kids with lots of recordings of images and voices from Earth. Lots of ethical concerns there!
    It is my opinion that by the time we have the technology to do that, robotics will have advanced enough to do the job and we wouldn't want to send people at all, unless we are establishing a new colony for the sake of procreation.
    I also think that whatever method is used, there is no point in a return trip. Rather send all the data back by radio waves and if you still have resources for more space travel, push on further out!
    However, even if the spacecraft travels at close to c, we wouldn't see the data for at least 400 years.

    I think that as soon as we develop drives close to c we should send out robotic spacecraft to all nearby star systems, rather like the voyagers but much faster.

    Does anyone know what the maximum velocity that can be obtained from slingshoting of plants is? Must you get closer to the planet the faster you go, and thus have a surface collision problem for higher speeds?
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