Are supermassive black holes just big stars?

  1. Simple enough question. I know there are two types of black holes; the type formed after a star collapses in a supernova and the supermassive variety like the one at the center of the milky way.
    If a star continued to grow by swallowing up other stars and solar systems is it possible that at a certain point its gravitational field would become so strong that light and heat could no longer escape? It would be a tipping point. Prior to reaching that mass it would be a bright star, but as it continued to grow it would start to dim as some wavelengths of the electromagnetic spectrum could no longer escape the massive star's gravitational field. Eventually it would reach such a size that it would appear dark to an observer, but in reality it is a bright and hot star that can no longer be conventionally detected.
  2. jcsd
  3. mathman

    mathman 6,750
    Science Advisor
    Gold Member

    (Not absolutely sure.) As long as the star is shining its volume would be too big to become a black hole. Once it runs out of fuel then things would happen.
  4. Seems likely that if you have enough mass in a small volume to keep photons from escaping, you have enough mass in a small volume that it will collapse into a black hole.

    Or it may be that a BH has to already BE there to keep photons from escaping.
  5. Nabeshin

    Nabeshin 2,202
    Science Advisor

    Indeed, this is a tautology by definition :)
  6. Ryan_m_b

    Staff: Mentor

    All wavelengths of light travel at the same speed, if the gravity is enough to stop one then it can stop all.
  7. Drakkith

    Staff: Mentor

    I don't believe this is possible. Wouldn't an existing star simply burn more fuel, resisting collapse?
  8. If that were true, how would ANY BH ever form? I think I must be missing something about what you are saying.
  9. Drakkith

    Staff: Mentor

    I'm not saying that it wouldn't EVER turn into a black hole, only that it wouldn't be a black hole until it runs out of fuel.
  10. Chronos

    Chronos 10,348
    Science Advisor
    Gold Member

    The Jeans mass limits the 'birth' mass of stars [which varies for Pop 1, II and III stars]. The mass limit for coalescence of stars is not well known. Stellar collisions are so extraordinarily rare in the univerve we have insufficient observational data to model the upper limit for these events. One thing, however, is well established, enormously massive stars simply do not live long enough to accrete a large amount of additional mass. Stars more than 100 solar masses only live for tens of millions of years, as compared to the sun, which has a life expectancy of around ten billion years.
  11. Ah, I KNEW there was something I wasn't connecting the dots with. Thanks.
  12. Hello all,

    As many of you have seen a few of my posts you will know I am not overly speculative, so I am in no way promoting this as a theory just want to know if anything along these lines has been pursued before:

    I have read somewhere that the early U may have had enormous stars, in orders of magnitude larger than current stars, would it be possible that the SMBH's at the center of each galaxy formed from these primordial massive stars? Or would we see evidence of this in the most distant galaxies? Are there any predictions for what massive objects formed the SMBH's or are they considered to merely have grown due to being "fed" stellar material for a few billion years?

    Any information is appreciated.
  13. mathman

    mathman 6,750
    Science Advisor
    Gold Member

    The early stars were (order of magnitude) around 100 solar masses.

    Black holes at galactic centers are of the order of millions to billions of solar masses. It seems unlikely that they could form from early stars without accumulating a lot more material.
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