Sloshing, supersonic gas may have built the baby universe’s biggest black holes

Sep 29, 2017

By Joshua Sokol

A central mystery surrounds the supermassive black holes that haunt the cores of galaxies: How did they get so big so fast? Now, a new, computer simulation–based study suggests that these giants were formed and fed by massive clouds of gas sloshing around in the aftermath of the big bang.

“This really is a new pathway,” says Volker Bromm, an astrophysicist at the University of Texas in Austin who was not part of the research team. “But it’s not … the one and only pathway.”

Astronomers know that, when the universe was just a billion years old, some supermassive black holes were already a billion times heavier than the sun. That’s much too big for them to have been built up through the slow mergers of small black holes formed in the conventional way, from collapsed stars a few dozen times the mass of the sun. Instead, the prevailing idea is that these behemoths had a head start. They could have condensed directly out of seed clouds of hydrogen gas weighing tens of thousands of solar masses, and grown from there by gravitationally swallowing up more gas. But the list of plausible ways for these “direct-collapse” scenarios to happen is short, and each option requires a perfect storm of circumstances.

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11 comments on “Sloshing, supersonic gas may have built the baby universe’s biggest black holes

  • @OP – Sloshing, supersonic gas may have built the baby universe’s biggest black holes

    Which clueless astro-duffer wrote this title about orbital velocities?

    https://en.wikipedia.org/wiki/Supersonic_speed

    Supersonic travel is a rate of travel of an object that exceeds the speed of sound (Mach 1).
    For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately 343 m/s 1,125 ft/s, 768 mph, 667 knots, or 1,235 km/h.
    Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic.

    Then we move UP to the speeds of planetary and stellar orbits!

    http://www.skyandtelescope.com/astronomy-news/star-speeds-around-milky-ways-black-hole/

    At its closest approach last March, the star swung within 17 light-hours of the hole, only three times the average distance of Pluto from the Sun. But while Pluto moves at a leisurely pace of less than 5 kilometers per second,
    S2 traveled more than 5,000 kilometers per second — proof of the enormous mass inside its tiny orbit. “The only compelling explanation is that there is a supermassive black hole lurking there,” writes Karl Gebhardt (University of Texas) in an accompanying Nature commentary.

    Even Pluto’s small mass in the weak gravity of the outer Solar-System has an orbital velocity far exceeding “hypersonic”!



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  • Alan,

    Supersonic technically means faster than the speed of phonons in a medium, or faster than acoustic pressure waves in a medium. Different media have different propagation speeds. (In many gasses it goes to a minimum around 1 bar.) Sonic pressure waves can (mostly) elastically dissipate (disperse) the acoustic energy. If they have so much energy (1/2mV^2 so velocity) they overcome the elastic limit of the medium, this results in the particles crashing into each other, even starting black holes.

    http://www.lpl.arizona.edu/~rlorenz/soundspeed.pdf



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  • phil rimmer #2
    Sep 29, 2017 at 1:46 pm

    Alan,

    Supersonic technically means faster than the speed of phonons in a medium, or faster than acoustic pressure waves in a medium.

    In gas nebulae I would expect that the molecules and atoms would be so widely spaced, that pressure waves would be very limited.

    Different media have different propagation speeds. (In many gasses it goes to a minimum around 1 bar.) Sonic pressure waves can (mostly) elastically dissipate (disperse) the acoustic energy.

    I am unclear as to how this is supposed to work, or why in a general article the speed of sound would be quoted in this context!

    Our usual concepts of speed of sound is orders of magnitude too slow for the usual processes of accretion disks orbiting or spiralling into stars, or gas clouds spiralling into black holes.

    I am not a physicist, so perhaps you could clarify some of these issues.



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  • Have a look at how the speed of sound varies on the gas giants with pressure in the attached paper.

    Here is some basic material.

    https://en.wikipedia.org/wiki/Bow_shocks_in_astrophysics

    Note the speed of sound in a gas (plasma in this case) is both proportional to pressure and inversely proportional to density. One might expect that ratio of pressure and density to preserve the speed of sound nominally constant over a range of pressures/densities. But its temperature that can increase pressure whilst density is constant.

    High temperature in very low density gas/plasma creates high speeds of sound. Likewise in high densities of gas.

    Whilst space is cold, bathed in photons of 2.3K, plasma particles are generally hot having very high individual velocities (not to be confused with the actual speed of sound in the medium) but hot particles will transmit their compression forces to their neighbours more quickly resulting in a higher speed of sound.

    I think the supersonic comment exactly describes the mechanism for crushing matter to arbitrarily high densities. The ejected plasma is the medium. The supersonic effect will happen somewhere in the middle of it.



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  • Sorry my first comments about pressure needed you to compare fig3 and fig6 in the gas giant paper. The speed of sound is varying most strongly in relation to temperature as later explained.



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  • phil rimmer #4
    Sep 29, 2017 at 3:17 pm

    High temperature in very low density gas/plasma creates high speeds of sound. Likewise in high densities of gas.

    It would appear that time-scales are important, as following the inflationary period, the energy of the Big-Bang was cooling and condensing into atoms, so was probably still hot at this stage.

    @OP – They could have condensed directly out of seed clouds of hydrogen gas weighing tens of thousands of solar masses, and grown from there by gravitationally swallowing up more gas.

    The density and dimensions of these clouds in the vacuum of space, would appear to be a key issue, with gas pressure acting against gravity, and generating heat as the gas was compressed.

    @OP – But the list of plausible ways for these “direct-collapse” scenarios to happen is short, and each option requires a perfect storm of circumstances.

    For theorists tinkering with computer models, the trouble lies in getting a massive amount of gas to pile up long enough to collapse all at once, into a vortex that feeds a nascent black hole like water down a sink drain.
    If any parts of the gas cloud cool down or clump up early, they will fragment and coalesce into stars instead. Once formed, radiation from the stars would blow away the rest of the gas cloud.

    Whilst space is cold, bathed in photons of 2.3K, plasma particles are generally hot having very high individual velocities

    I find this unclear. If stars have not yet formed in those regions, where are these photons coming from?

    (not to be confused with the actual speed of sound in the medium) but hot particles will transmit their compression forces to their neighbours more quickly resulting in a higher speed of sound.

    Thanks for the links about higher speeds of sound in extraterrestrial conditions.

    We know that supernova explosions cause shock waves in nearby gas clouds to form stars, but before the first stars formed, shock waves must have been generated by some other means.

    I think the supersonic comment exactly describes the mechanism for crushing matter to arbitrarily high densities. The ejected plasma is the medium. The supersonic effect will happen somewhere in the middle of it.

    There would appear to be distinct phases with radically different conditions, before, during, and after, initial black hole formation.



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  • phil rimmer #5
    Sep 29, 2017 at 3:37 pm

    Sorry my first comments about pressure needed you to compare fig3 and fig6 in the gas giant paper. The speed of sound is varying most strongly in relation to temperature as later explained.

    Thank your for the links.

    Even with your higher fig.6 velocity of “sloshing, supersonic gas”, there is a considerable contrast between the speed of sound up to the 1600 metres/sec. in figure 6 on your link, and the 5,000 kilometers per second of matter approaching a large black hole, or even the low gravity orbit of Pluto at less than 5 kilometers per second, as linked at #1.

    I still have a problem with understanding how this matter at this velocity is accreting into black holes, although the paper is suggesting some sort of interaction with dark matter building up pressure waves.!



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  • I am only explaining why supersonic is a valid concept here. My account is only with regard to the references quoted. I’m afraid I haven’t read the OP.

    “Supersonic” means super compression, because above the “elastic limit”. The degree of compression is a matter of the energy of the event. There is no upper limit on this. The 2.3K was mentioned in relation to the Wiki article to illustrate the unusual definition of what the temperature in a region of space is and how it doesn’t relate to say the temperature of gas or plasma particles when they are low density.



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  • Clarification.

    Even with your higher fig.6 velocity of “sloshing, supersonic gas”,

    The gas giant paper was an illustration of the varying speeds of sound. There is nothing in the paper to do with “supersonic”. It is only we, looking at, it can now see that supersonic (a speed above the speed of sound) is contingent on context. (I possibly could have found a better paper for this point. But it came quickly to hand.



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  • phil rimmer #8
    Sep 29, 2017 at 6:54 pm

    The 2.3K was mentioned in relation to the Wiki article to illustrate the unusual definition of what the temperature in a region of space is and how it doesn’t relate to say the temperature of gas or plasma particles when they are low density.

    While I appreciate the limited energy transfers of high temperature particles in very low density materials in space, due to a lack of matter, low densities are not conducive to massive accretion processes. This is one of the puzzling aspects of this OP article.

    Perhaps some intense localised condensation of matter would bypass the accelerations to extreme velocities which would occur if that huge mass of diffuse gas was to accrete around a barycentre to form a black hole.



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  • We don’t know what the gas densities are nor the energy in a supersonic compression wave from the article. The “sloshing” may suggest interference patterns (like the multiple sloshing of waves in a pool) perhaps creating extra dense interference nodes a few of which are coincident with nascent black holes.

    It may just be that a sheet of hyper compressed gas makes a more efficient feedstock for black holes than merely compressed or uncompressed gas, the black hole being able to take a much bigger gravitational bite. Sloshing may indicate repeated hyper compressed waves growing the black hole especially rapidly.



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