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How were early galaxies formed?

  1. Feb 8, 2015 #1
    The early universe would appear to be contain more material per unit volume than now.This would then gve rise to a first generation big stars and an early develoment of supernova.
    My interest lies in the inevitable momentum that would be transferred by slingshot from pairs or groups of black- holes as they pass thorough a relatively dense environment.The trajectory of such material will be governed by the aquired momentum and the velocity away from the shared gravity well.
    The trajectory reminds me of water from a lawn sprinkler and over much time could contribute to the classical "galactic" spiral.
  2. jcsd
  3. Feb 8, 2015 #2
    Check out http://en.wikipedia.org/wiki/Density_wave_theory which explains the spiral structure as a result of standing density waves. I think the idea is that as an orbiting star approaches an over dense region, gravitational force will accelerate it towards the dense region. On the way out of the dense region, the star will be pulled back. The result is that the stars clump up in the dense region, causing a visible pattern. The differential rotation of a galaxy (slower orbits further from the center) will generally cause a disturbance like this to shear into a spiral shape on the galactic scale. The cause of an over dense region could be tidal forces from another galaxy, a supernova shockwave, etc.
  4. Feb 9, 2015 #3
    Big stars are the brightest

    Spiral arms are concentrations of star formation... Where big stars form and soon SN

    The only stars to live long enough to escape the arms are the smaller redder ones... So forming the disk of the galaxy

    Is that not true?
  5. Feb 9, 2015 #4
    I think part of the theory is that a dust cloud would be compressed as it enters a dense region, causing lots of star formation. It seems like those big stars would contribute most of the light for the spiral pattern.
  6. Feb 9, 2015 #5
    Except that there would not be any dust in the early universe. There would only be hydrogen, with a small amount of helium. How these first Population III stars formed still remains a mystery, but ESA's Planck satellite suggests that they did not form until ~550 million years after the Big Bang.
  7. Feb 9, 2015 #6


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    I was not aware that there WERE any black holes in the early universe, other than perhaps micro ones. Do you have a citation for that concept?
  8. Feb 9, 2015 #7
    I thought dust was a broad term that includes molucular clouds of hydrogen that would exist in the early universe. Either way, the result would be star formation.
  9. Feb 9, 2015 #8
    Primordial black holes are theoretically possible. They would have had to form within the first second after the Big Bang (before the end of the Hadron Epoch) when pressures and temperatures were still high enough to create black holes. The first stellar black holes obviously could not have formed until after the first Population III stars formed.

    Primordial Black Holes: Sirens of the Early Universe
    Last edited: Feb 9, 2015
  10. Feb 9, 2015 #9
    Cosmic dust is anywhere from few molecules to 0.1 µm in size, with each grain having a mass of approximately 10−17 kg. Cosmic dust is produced either by supernovae or asymptotic giant branch stars. Which means that cosmic dust could not have existed before the first Population III stars.
  11. Feb 9, 2015 #10


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    Right, I should have been more clear that I'm aware of the theory of primordial black holes but pretty clearly he was not talking about tiny ones at all.
  12. Feb 10, 2015 #11

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    Cosmologists have long had a chicken and egg problem: Which came first, galaxies or the black holes at the hearts of galaxies? Thinking has gone back and forth, but the current thoughts appear to be that large (but not yet supermassive) black holes preceded the formation of the first proto galaxies.

    I'll try to add some references in the literature later. For now, I'll leave you with this NPR All Things Considered interview with UT-Austin astrophysicist Karl Gebhardt and this blog post on What came first, black holes or galaxies? by Ethan Siegel.
  13. Feb 10, 2015 #12
  14. Feb 10, 2015 #13


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    It is clearly a challenge to explain the supermassive black holes believed to reside in high z quasars without some kind as of yet unknown black hole formation mechanism in the very early universe.
  15. Feb 11, 2015 #14
    Would not the very large Population III stars form black holes in short order (as in within a few million years)? We know that Population I and II stars will form black holes if they have a mass greater than 10 solar masses and less than 130 solar masses, but they would take to long to form black holes before galaxies formed. It has also been theorized that stars with between 130 and 250 solar masses create pair-instability supernovae, which do not leave black holes. It is my understanding, however, that Population III stars were even more massive, ranging from 250 solar masses to well over 1,000 solar masses. I am not sure whether or not they would leave a black hole upon their death, but their life-span would be very short, well under a million years for the more massive Population III stars. As these massive Population III stars die out, assuming they leave black holes in their wake, that could be the mechanism required to start forming galaxies.
  16. Feb 12, 2015 #15


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    That is one possibility, but , does not entirely satisfy Jeans mass limits. It is, however, still considered possible ancient black holes may have formed via direct collapse -bypassing the pop III stellar scenario.
  17. Feb 12, 2015 #16


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    Apropos the title of this thread, one early galaxy at z=6.34 i.e. 0.868 Gyrs. after BB. (Ned Wright's Calculator) - HFLS3 - a record-breaking galaxy


    (Emphasis mine)

    Going back to the OP questions about BH's; did any form at this time?

    Well we would have to look at the high energy (gamma or X ray) end of the spectrum, not optical/IR/sub-millimetre as above.

    A most distant GRB is GRB 090423 subsequently identified by its IR afterglow at z=8.2. (618 Myr after BB) Even earlier (further) than the distant galaxy.
    Those Pop III's were very busy - unless as Chronos suggested BH's formed by direct collapse.

    A lot happened very quickly!!

    Last edited: Feb 12, 2015
  18. Feb 12, 2015 #17
    According to ESA's Planck satellite, they have recently placed reionization, or the first formation of stars, at ~550 million years after the Big Bang. Which would only leave ~318 million years to form galaxies (assuming GRB 090423 is one of the oldest). That does not seem like much time, but when you consider that a 250 solar mass star has a lifespan of ~10,000 years, and a 1,000 solar mass star has a lifespan of less than 500 years, that is a lot of supernovas, or direct collapsing, going on in a very short period. In ~318 million years there is not likely to be any Population III stars remaining.
  19. Feb 13, 2015 #18


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    Agreed - and we ought to be able to detect those 'hypernovae' any time now....

    Even though there was enough time for the Pop III's to evolve the question arises of how did primordial galaxy formation, BH accretion and Pop III formation happen in ~ 300Myrs?

    For example, with low or near zero metallicity, Pop III formation would be difficult as the collapsing nebula - Bok globule, would find it difficult to radiate the heat away. Normally dust particles as efficient radiators are important at this stage.

  20. Feb 13, 2015 #19
    A prominent textbook observes that while larger galaxies have central SMBH, their smaller relatives have nuclear star clusters NSC. The NSC seem to obey the same scaling law for mass compared to surrounding galaxy, and there may be some evolutionary connection between them, which I think means NSC might gravitationally settle until the core is so dense with stars that it collapses into a SMBH
  21. Feb 13, 2015 #20
    I agree, that does pose a problem. Without cosmic dust, you are not going to have Bok globules. There is also the Jeans mass problem. The hydrogen nebula should have collapsed into a star, or directly into a black hole, before reaching 250 solar masses. So how could such super-massive stars exist? With no cosmic dust and super massive stars in the early universe, there must have been some other mechanism involved in their creation.
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