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  • UY Scuti is a star 1 billion times the volume of our sun.
  • A billion solar mass black hole formed 750 million years after the Big Bang.

Could it have formed from a star like UY Scuti?

Rare black hole 1 billion times the mass of the sun could upend our understanding of galaxy formation

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    $\begingroup$ are we talking about stars or black holes? The most massive star known to date has a mass of 226 solar masses (226 $M_\odot$). A star with a mass of 1 million solar masses would be something phenomenal en.wikipedia.org/wiki/List_of_most_massive_stars Overall, an interesting question! $\endgroup$
    – dtn
    Sep 28, 2023 at 16:34
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    $\begingroup$ "What is the biggest star in the universe? | Space" space.com/41290-biggest-star.html $\endgroup$
    – user52394
    Sep 28, 2023 at 17:17
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    $\begingroup$ Your question starts off talking about volume, then switches to mass. Which do you mean? $\endgroup$ Sep 29, 2023 at 8:27
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    $\begingroup$ @Mark Morgan Lloyd I wrongly assumed mass was proportional to volume. $\endgroup$
    – user52394
    Sep 29, 2023 at 10:50
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    $\begingroup$ It is theoretically possible to have stars on the order of a million solar masses, but they are very short lived. en.wikipedia.org/wiki/Quasi-star $\endgroup$ Sep 29, 2023 at 14:45

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UY Scuti is a hypergiant star. The name refers to its size, not its mass. It may well have a billion(ish) times the volume of the Sun, but it is only about ten times the mass of the Sun.

A supergiant/hypergiant is an evolutionary phase that at least some massive (10-100 solar mass) stars go through, shortly before the ends of their lives. There is no special formation mechanism - the envelope inflates and becomes very tenuous as a result of the physics of what is going on inside the star - a more extreme version of the giant phase that even the Sun will eventually go through.

Supermassive black holes do not form directly from stars. There was no billion solar mass stellar progenitor. The formation mechanism is somewhat mysterious but likely involves the accretion of lots of gas or the merger of lots of black holes.

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    $\begingroup$ @DaveTheWave Where did you find that 30 solar masses figure? Everything I've read says seven to ten solar masses. $\endgroup$ Sep 28, 2023 at 18:29
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    $\begingroup$ Also bear in mind that to have one billion times the volume of the Sun, it "only" has 1000 times the radius (actually maybe more like 1700, that "one billion" is just the order of magnitude). 1000 solar radii is approximately the distance from the Sun to Jupiter. So, once you believe the Sun will inflate to approximately the Earth's orbit, then it's probably not such a surprise that other stars inflate a few multiples further. $\endgroup$ Sep 29, 2023 at 8:49
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    $\begingroup$ @DaveTheWave: The reason population III stars are said to have low metal content, is that prior to population III stars it seems there was nothing to produce heavier elements. So I don't think it's really curious: population III stars were formed from H and He, they started producing heavier elements, therefore later stars (including UY Scuti) can have higher metallicity. Of course this is conjecture, but a difference in composition between early and late stars isn't a reason to doubt the existence of early stars: it's predicted by the theory. $\endgroup$ Sep 29, 2023 at 9:03
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    $\begingroup$ @DaveTheWave: sorry, I don't know the details of the proposed formation of population III stars. Just from a Google search, aanda.org/articles/aa/full_html/2015/09/aa26617-15/… talks about formation of large low-metallicity stars, and I think even without talking about population III it's not controversial that high-mass low-metallicity stars do exist. Quoting that introduction, "low-metallicity massive stars can also be found in the local Universe: some of the nearby dwarf galaxies form massive stars at a high rate (Tolstoy et al. 2009; Weisz et al. 2014)" $\endgroup$ Sep 29, 2023 at 11:39
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    $\begingroup$ So, if you're going to say that pop III cannot have existed because large low-metallicity stars cannot exist, then you need some other way to explain what appear to be observations of large low-metallicity stars. $\endgroup$ Sep 29, 2023 at 11:43
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You are confusing volume with mass. While UY Scuti is indeed five billion times the size of the Sun in terms of volume, it is only seven to ten times the size of the Sun in terms of mass. That most likely is not massive enough to form a black hole at the time of its death. It will instead form a neutron star. That neutron star might combine with another to form a black hole, which might in turn combine with other stellar mass black holes to form intermediate mass black holes.

The formation of supermassive black holes is still a bit of a scientific mystery. That they exist is not a mystery. That they exist is a scientific fact.

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    $\begingroup$ You are right 7 to 10 solar masses I mixed up a volume with mass. $\endgroup$
    – user52394
    Sep 28, 2023 at 18:39
  • $\begingroup$ Small radiating black holes could have caused reionizamtion instead of population 3 stars. $\endgroup$
    – user52394
    Sep 28, 2023 at 18:41
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Supermassive black holes are believed to form through several processes, like massive early (population III) stars massing up to a thousand or more solar masses, accretion in very dense environments, and mergers with other black holes. Early supermassive black holes are trickier to explain, but there may have been overdense regions of the early universe where dark matter halos got inside its own Schwarzschild radius and collapsed, or metal-free gas clouds that collapsed. But it is an active research area with many unknowns right now.

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The formation of stars like UY Scuti and black holes with a billion solar masses involves different processes and timescales, and they are not directly related in the way one might initially think.

Formation of Massive Stars like UY Scuti

UY Scuti is a red supergiant star, and while it is indeed about a billion times the volume of our Sun, it is not a billion times the mass. Its mass is estimated to be around 7-10 times that of the Sun. Stars like UY Scuti form from massive molecular clouds in a process that involves the gravitational collapse of gas and dust. The mass of the star is determined by the initial conditions in the molecular cloud, including its density and temperature.

Formation of Billion Solar Mass Black Holes

Black holes that are a billion times the mass of the Sun are generally thought to form in the centers of galaxies and are the result of multiple processes, including the collapse of massive stars into smaller black holes, which then merge and accrete mass over time. The formation of such massive black holes so soon after the Big Bang is still a subject of research and debate among astrophysicists. One leading theory is that they form through the direct collapse of large gas clouds, bypassing the star formation stage entirely.

Could a Star Like UY Scuti Turn Into a Billion Solar Mass Black Hole?

The short answer is no. When UY Scuti exhausts its nuclear fuel, it will likely undergo a supernova explosion and may form a black hole. However, the resulting black hole would be much smaller, on the order of 10 solar masses, not a billion. The process of forming a billion-solar-mass black hole involves not just the end stages of one star's life but likely the complex interplay of many stars and other black holes, as well as the accretion of a large amount of matter over a long period.

Implications for Our Understanding of Galaxy Formation

The discovery of black holes with a billion solar masses so soon after the Big Bang does challenge our understanding of galaxy formation and black hole growth. It suggests that there are mechanisms for black hole formation and growth that are faster than those currently understood, which has implications for theories of cosmic structure formation.

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  • $\begingroup$ @Heylts Tony I should think that black holes form quickly because of magnetic fields bringing them or the stars or gas that form them closer together . "impact of magnetic fields on cosmological galaxy mergers – II. Modified angular momentum transport and feedback | Monthly Notices of the Royal Astronomical Society | Oxford Academic" academic.oup.com/mnras/article-abstract/526/1/224/… $\endgroup$
    – user52394
    Sep 29, 2023 at 7:53
  • $\begingroup$ HeyItsTony ... adding two spaces to the end of a line, followed immediately by an 'enter' will force a phrase/sentence to the next line. When you originally posted your answer, your header lines were commingled with the paragraphs... fixed and italicized. $\endgroup$
    – CGCampbell
    Sep 29, 2023 at 12:30

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