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Thread: Question about First-Gen Star Formation

  1. #31
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    Quote Originally Posted by Ken G View Post
    Yes, it would probably have to be more than just tidal effects. Presumably gas pressure would be involved. Without walls.
    That's one of the two options. Either gas and stars are separated by galaxy collisions, or they already are separated in galaxy before collisions.

  2. #32
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    Yes, and judging from the bullet cluster, I favor the former.

  3. #33
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    First-generation Population III stars may have commonly formed in double or multiple systems. https://arxiv.org/abs/2002.00012 (computer simulations)
    Do good work. —Virgil Ivan "Gus" Grissom

  4. #34
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    Quote Originally Posted by Roger E. Moore View Post
    First-generation Population III stars may have commonly formed in double or multiple systems. https://arxiv.org/abs/2002.00012 (computer simulations)
    Would the situation for the first stars forming in the galaxy have been the same for Pop3 stars, or is that already Pop2. Would the first stars to form in the galaxy have had the same distribution as those that form later. I am wondering if the earliest stars to form in the galaxy have been multiple systems, and distributed in a spherical halo with virilised orbits.

    I am wondering if the early population of multiple stars systems would form the population of tired systems that end up at the galactic centre being collapsed to form the G-clouds?

  5. #35
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    Quote Originally Posted by transreality View Post
    ... Would the first stars to form in the galaxy have had the same distribution as those that form later. I am wondering if the earliest stars to form in the galaxy have been multiple systems, and distributed in a spherical halo with virilised orbits.

    I am wondering if the early population of multiple stars systems would form the population of tired systems that end up at the galactic centre being collapsed to form the G-clouds?
    I haven't spotted any papers about this topic (doesn't mean there weren't any). How much of the galactic disk had formed when the Pop-3 stars formed? probably not much of one, since the earliest galaxies we observe at Z>7 are all irregular looking. Based on that, I am guessing that IF Pop-3 stars left remnants they would be at best in the thick disk, or perhaps distributed in a somewhat flattened spherical halo. Note that we have observed a few extremely low metal stars (VERY old red dwarfs) and they are well outside the main disk.


    Also, as I understand current thinking on these topics, the G-clouds are not nearly massive enough to be Pop-3 stars.
    Forming opinions as we speak

  6. #36
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    Here is a paper on Pop III galaxies, but I am unsure if this answers your questions above.

    https://ui.adsabs.harvard.edu/abs/20....178K/abstract

    Fragmentation in Population III Galaxies Formed through Ionizing Radiation
    Kulkarni, Mihir ; Visbal, Eli ; Bryan, Greg L.

    Population III stars forming in minihalos tend to be relatively inefficient, with each minihalo hosting one or a small number of stars which are more massive than local stars, but still challenging to observe directly at high redshift. Here we explore a possible mechanism for the generation of larger clusters of such stars: a nearby ionizing source that ionizes a late forming halo, delaying its collapse until the halo is sufficiently large enough that the core can self-shield and suffer runaway collapse. We use simulations with a simple but accurate model for the radiative ionizing flux and confirm the basic predictions of previous work: higher ionizing fluxes can delay the collapse to lower redshifts and higher masses, up to an order of magnitude above the atomic cooling limit. In a limited number of runs we also examine the fragmentation of the cores at even higher resolution, using both simple estimates and sink particles to show that the number of fragments is generally small, at most a handful, and that the mass accretion rate on the fragments is of order 10-3 M ☉ yr-1. This rate is sufficiently high enough that the descent on the main sequence (and hence the suppression of accretion) is delayed until the stellar masses are of order 100-1000 M ☉, but not high enough to produce direct collapse black holes of mass ̃105 M ☉. The resulting clusters are larger than those produced in minihalos, but are still likely to fall short of being easily detectable in James Webb Space Telescope blind fields.

    ===

    And another recent book chapter.

    https://arxiv.org/abs/1807.06248

    Formation of the first stars
    Ralf S. Klessen (Heidelberg University, Center for Astronomy)
    (Submitted on 17 Jul 2018)

    From studying the cosmic microwave background, we know our Universe started out very simple. It was by and large homogeneous and isotropic, with small fluctuations that can be described by linear perturbation theory. In stark contrast, the Universe today is highly structured on a vast range of length and mass scales. In the evolution towards increasing complexity, the formation of the first stars marks a primary transition event. The first generation of stars, the so-called Population III (or Pop. III) build up from truly metal-free primordial gas. They have long been thought to live short, solitary lives, with only one massive star forming per halo. However, in recent years this simple picture has undergone substantial revision, and we now understand that stellar birth in the early Universe is subject to the same complexity as star formation at present days. In this chapter, I review the current state of the field. I begin by introducing the basics concepts of star-formation theory and by discussing the typical environment in which Pop. III stars are thought to form. Then I argue that the accretion disk that builds up in the center of a halo is likely to fragment, resulting in the formation of a cluster of stars with a wide range of masses, and I speculate about how this process may be influenced by stellar feedback, the presence of magnetic fields, the energy input from dark matter annihilation, and the occurrence of large- scale streaming velocities between baryons and dark matter. Finally, I discuss direct and indirect constraints on Pop. III star formation from high-redshift observations and from the search for extremely metal-poor stars in the Milky Way and its satellites.
    Last edited by Roger E. Moore; 2020-Feb-11 at 02:49 PM.
    Do good work. —Virgil Ivan "Gus" Grissom

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