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Would a Hot star have more mass than a cooler one?

  1. Aug 2, 2004 #1
    If you had 2 identical stars, one was a very hot star, but the other was cooler. Since mass is relative to velocity, shouldnt the hotter star be more massive than the cooler one since the atoms in the hotter star would have more kinetic energy and therefore a higher speed?
     
  2. jcsd
  3. Aug 2, 2004 #2
    If you had the cool star and energy was added to it to make it hot, then it would be more massive than it was when it was cool. I don't know if your analogy works because if one was hotter than the other they wouldn't be identical. But you're right; adding heat, or any kind of energy, to anything makes that thing more massive.
     
  4. Aug 2, 2004 #3

    turin

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    Can you clarify what you mean by "identical stars?"
     
  5. Aug 2, 2004 #4

    Nereid

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    Be sure too, when answering turin's question, to tell us whether the 'stars' are in some kind of equilibrium or not ... e.g. not in the process of exploding or collapsing :wink:
     
  6. Aug 2, 2004 #5

    Doc Al

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    Is the question really about stars, or is it about whether heating something up increases its mass? If it's the latter, choose a simpler example: two identical steel chunks, say. Now heat one up. Does its mass increase?
     
  7. Aug 2, 2004 #6
    What you meen by identical stars is confusing.
    but if you take a black hole which,supposedly has an infinite mass,. Is this black hole hotter than a star such as a hypernova or supernova?. basically because a black hole is/was a star that burnt its fuel so quickly that it collasped uder the force of its own gravity, then i would assume that the temperature would not be the only consideration in this.
    Am I right.
    jamie
     
  8. Aug 2, 2004 #7

    turin

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    No black hole that I've heard of is supposed to have an infinite mass. All the ones I've heard of have masses less than a galaxy's worth. I don't think they have temperature, though, or, if they do, it is extremely low (down at the Hawking radiation level, if such a mechanism truly exists).
     
  9. Aug 2, 2004 #8
    hello turin
    nothing has infinite mass because this would violate the laws of the conservation of energy.
    now many times i have seen on this forum, and others, people refering to infinite mass/energy in the case of singularities.
    this is why i used the term suposedly
    regards jaime
     
  10. Aug 3, 2004 #9
    Hey all, sorry about the confusion. By saying identical stars, i meant that the stars (if would be the same temperature) would have the same mass, and i guess the same concentration of H and He atoms, although i dont think thats neccasary to say in this case. Lets just say you first have 2 identical stars, later one stays the same, while the other heats up. I guess you can say one grows old while one stays young. Assuming that there is no other outside influence on the 2 stars, the hotter star should have more mass shouldnt it? Seems to me that it should.
     
  11. Aug 3, 2004 #10

    Nereid

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    Hmm, I'm still confused as to whether you're looking for a mass-temperature effect, or something about stellar evolution.

    Since you've posted in Classical Physics, and not in Stellar Astrophysics (or Astronomy & Cosmology), my guess is, as Doc Al said, the former.

    If, however, it's stellar evolution you're interested in, then your question can't be answered. Why? because if you have two identical stars, they will evolve in the same way, so it's not possible that 'later one stays the same, while the other heats up'. Also, for stars, it's not clear what you mean by 'heats up' - while it's relatively straight-forward to determine the effective temperature of the photosphere (a star's 'surface'), that's only the temperature of a small fraction of its total mass; for example, the core has a very much higher temperature.
     
  12. Aug 4, 2004 #11
    The whole point i was making wasnt star evolution, but the fact that if one star has a greater temperature than the other then that would mean that the atoms that the star is made up of have a higher kinetic energy and therefore a higher speed. Mass is relative to speed, so if the atoms of one are moving faster than the atoms of the other, then one must have a greater mass.
     
  13. Aug 4, 2004 #12

    pervect

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    Yes, the hotter star has a higher mass. One has to be able to consider the star as an isolated system (that's not a problem here) within an asymptotically flat space time (that's not a problem here either) to fully justify this statement.
     
  14. Sep 29, 2011 #13
    It's not an increase in rest mass. It's an increase in total mass, however, including energy.

    E = mc^2.

    Therefore, m = E/(c^2)

    And about the infinite mass/energy singularity, I think it's supposed to be infinite density, not mass. Density is the mass/volume, so dividing mass by a volume approaching 0 means a density approaching infinity.
     
  15. Sep 29, 2011 #14

    Vanadium 50

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    This thread is seven years old.
     
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