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Collapsing Stars on the H-R diagram

  1. Sep 7, 2011 #1
    Hi, I've been looking at the Hertzsprung-Russel diagram and was wondering exactly what types of stars collapse to form a black hole? What temperature range/radius etc. turn into black holes. I understand that its most likely the supergiants that form black holes, but what about the giants? Are they too small?
  2. jcsd
  3. Sep 8, 2011 #2


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    A giant star is simply a star with greater radius and luminosity than a main sequence star of equal temperature. It doesn't have anything to do with the mass. However, stars do need a minimum of mass to reach the giant stage. According to wikipedia they need greater than 0.25 solar masses.

    For a star to collapse into a black hole, the core needs a minimum amount of mass when it reaches the point where it can no longer hold itself up over gravity. I believe this is somewhere between 1.5 - 3.0 solar masses. Note that this is the mass of the core, not the entire star itself. A large percentage of a stars mass will be ejected in the supernova of the collapse, with only the core itself actually collapsing. I would guess that SOME giants can collapse into a black hole, but I really don't know the required inital mass range a star needs.

    Interestingly, stars above a certain mass will actually blow themselves apart from the core outwards without leaving a neutron star or black hole, meaning that black holes can only form from stars in a range of masses with a minimum and maximum value.
  4. Sep 8, 2011 #3
    We don't know enough about how supernova work to know the exact dividing line. We are pretty sure that things over 40 solar mass will end up as a black hole and things that are under 15 solar masses will end up as a neutron star. Where the exact dividing line is, we don't know.

    Also it could be different for different stars. If a large star has a lot of mass loss because of it's environment, it could behave differently than a small star that doesn't.
  5. Sep 8, 2011 #4
    This is one of the uncertain things. In order to calculate that number we need to know how "stiff" nuclear material is, and we don't. If nuclear material is stiff they you need more of it to collapse into a black hole.

    That's cool. No one else does either. We don't know enough about supernova and massive star evolution to go from initial mass to final mass. We know enough to set some limits (i.e. 10 solar mass will not be a black hole. 40 solar mass will), but we don't know enough to figure out the details.

    One of the things that I wanted to do with my Ph.D. dissertation was to figure out what the limit was. After seven years of doing my dissertation, I came to the conclusion that what I was doing wouldn't come up with the answer, and so this is a mystery of the universe that someone else needs to take a crack at.

    Most of these calculations are done using computer simulations, which can be quite complicated.

    That's about 100 solar mass at which point you get a weird pair-production supernova. Also stars in the early universe when there was nothing other than hydrogen/helium are likely to behave very differently than stars today.
  6. Sep 8, 2011 #5


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    Exactly twofish! So interesting!!
  7. Sep 9, 2011 #6
    thanks for all the replies, it was very enlightening. I would like to know about your thesis twofish-quant.
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