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Question about the sun and the earth long long ago.

  1. Aug 30, 2007 #1
    I might already know the answer to this but i just need to make sure. Does a suns mass reflect its volume? I ask because...

    The formation of a star simply put is: a planet gathers mass there-by gathering gravity there-by igniting and becoming a star…it becomes a star with x amount of mass to start then burns and burns and burns until it looses enough stuff to burn causing an implosion then an explosion(super nova). Correct??

    So if this is true where was earth when our sun was reeeeeeeeealy big? Is it not true that the sun looses x amount of mass a year and by rewinding the whole sequence you should be able to see how big the sun was say about 4.6 billion years ago? If around that time say a planet was trying to evolve wouldn’t the sun have pulled this planet in leaving it, well, not there? Seeing how the sun loses a lot of mass now, 4.6 billion years ago would put the sun at…BIG (at least I assume big enough to reach our orbit) we’ll say maybe too big for the earth to be just kinda hanging around unharmed. Now let’s move 1.6 billion years ahead. Somehow this planet survived orbiting closely or even within the sun, 1.6 million years should shrink the sun a bit. About this time this planet starts to have life appear, the sun would still be really close, close enough to be super heating the earth and kill those pesky possible life forms. I don’t know the #’s but I’m sure some of you do.
    How much mass the sun is loosing at present/year (x)
    Y + present day mass of sun = mass of sun 4.6billion years ago. (We’ll call this z)
    Now how much volume would the sun fill with (z) amount of mass? Or would the same amount of volume hold greater amounts of mass? Leaving the sun heavier but none the more bigger
  2. jcsd
  3. Aug 30, 2007 #2


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    Main sequence stars don't loose much mass, there is a tiny (by comparison to their size) amount thrown out as the solar wind.
    The sun will expand as it enters the red giant phase and will oddly then begin to lose mass - upto 25% of the outer envelope is ejected.
    Depending on how much mass is lost the earth's orbit may increase so that it escapes being swallowed by the larger sun, but either way it is going to get severly roasted.

    ps. Our sun is not large enough to supernova, it will expand to a large low density red giant and then a small core will be left as a white dwarf.

    As an example of the range of densities, Betelgeuse (the red star at Orion's shoulder) is about 14times the mass of the sun but 650 times the radius, so it has about 275Million times the volume but only 1/20 millionth the density.
    Last edited: Aug 30, 2007
  4. Aug 30, 2007 #3
    Excellent; thanks!!
  5. May 22, 2009 #4
    Red Giant Branch and Asymptotic Giant Branch stars are really just small dense fusion cores surrounded by a very BIG atmosphere. The two parts of the star don't mix and the outer layers eventually get blown away. Smaller stars - smaller than the Sun - are more like the cores of bigger stars. For example, a 0.1 Solar mass red-dwarf star is just 0.125 times the size of the Sun, meaning its average density is 51.2 times the Sun's and its surface gravity is 6.4 times stronger.
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