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Thread: The giant moths circling the center of our galaxy

  1. #1
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    Exclamation The giant moths circling the center of our galaxy

    The most fascinating discovery (for me) for quite a long while. What are these things? They orbit the supermassive black hole like titanic, gaseous moths.


    https://phys.org/news/2020-01-astron...-enormous.html

    Astronomers discover class of strange objects near our galaxy's enormous black hole
    by University of California, Los Angeles
    January 15, 2020

    Astronomers from UCLA's Galactic Center Orbits Initiative have discovered a new class of bizarre objects at the center of our galaxy, not far from the supermassive black hole called Sagittarius A*. They published their research today in the journal Nature. "These objects look like gas and behave like stars," said co-author Andrea Ghez, UCLA's Lauren B. Leichtman and Arthur E. Levine Professor of Astrophysics and director of the UCLA Galactic Center Group. The new objects look compact most of the time and stretch out when their orbits bring them closest to the black hole. Their orbits range from about 100 to 1,000 years, said lead author Anna Ciurlo, a UCLA postdoctoral researcher.

    MAIN PAPER: https://www.nature.com/articles/s41586-019-1883-y
    The central 0.1 parsecs of the Milky Way host a supermassive black hole identified with the position of the radio and infrared source Sagittarius A* (refs. 1,2), a cluster of young, massive stars (the S stars3) and various gaseous features4,5. Recently, two unusual objects have been found to be closely orbiting Sagittarius A*: the so-called G sources, G1 and G2. These objects are unresolved (having a size of the order of 100 astronomical units, except at periapse, where the tidal interaction with the black hole stretches them along the orbit) and they show both thermal dust emission and line emission from ionized gas6,7,8,9,10. G1 and G2 have generated attention because they appear to be tidally interacting with the supermassive Galactic black hole, possibly enhancing its accretion activity. No broad consensus has yet been reached concerning their nature: the G objects show the characteristics of gas and dust clouds but display the dynamical properties of stellar-mass objects. Here we report observations of four additional G objects, all lying within 0.04 parsecs of the black hole and forming a class that is probably unique to this environment. The widely varying orbits derived for the six G objects demonstrate that they were commonly but separately formed.
    Do good work. —Virgil Ivan "Gus" Grissom

  2. #2
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    Quote Originally Posted by Roger E. Moore View Post
    The most fascinating discovery (for me) for quite a long while. What are these things? They orbit the supermassive black hole like titanic, gaseous moths.




    Astronomers discover class of strange objects near our galaxy's enormous black hole
    by University of California, Los Angeles
    January 15, 2020
    It seems they are the collapsed remnants of multi-star systems that get so close to the black hole, that the stars that were orbiting each other collide and merge to form a new star in the process of already being gas stripped. Since the central area is orbited by a bunch of single stars in relatively stable orbits, does this mean that binary stars are going to be more likely to end up supply the gas of an accreting black hole?

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    I wonder if these observations are part of the phenomenology of Walker and Wardle's AU-sized gas clouds, e.g:

    https://arxiv.org/abs/astro-ph/0610737

    https://arxiv.org/abs/1906.01141

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    Universe Today's information on the new G objects...

    https://www.universetoday.com/144654...the-milky-way/
    Do good work. —Virgil Ivan "Gus" Grissom

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    Quote Originally Posted by Roger E. Moore View Post
    Universe Today's information on the new G objects...

    https://www.universetoday.com/144654...the-milky-way/
    ...But no mass estimates?

    Having a merged binary star system in the middle implies a stellar mass. But there is no direct observation of a star at the centre.

    Has anyone seen an estimate of the mass, based on the amount of distortion and the tidal forces experienced by the clouds?

  6. #6
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    Quote Originally Posted by transreality View Post
    Since the central area is orbited by a bunch of single stars in relatively stable orbits, does this mean that binary stars are going to be more likely to end up supply the gas of an accreting black hole?
    I think it just means close binaries get turned into single stars before they fall in. I presume all those stars will eventually fall in, or there'd be a lot more of them orbiting by now. The puzzle is how did they get there in the first place-- they are young stars, so it is thought they should have had to form nearby, but how did they form in an environment that is trying to rip off shells from them? We think stars need to form in giant molecular clouds, but why wouldn't the clouds be shredded by the SMBH? I don't know if that's been resolved yet.

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    Quote Originally Posted by Ken G View Post
    I think it just means close binaries get turned into single stars before they fall in. I presume all those stars will eventually fall in, or there'd be a lot more of them orbiting by now. The puzzle is how did they get there in the first place-- they are young stars, so it is thought they should have had to form nearby, but how did they form in an environment that is trying to rip off shells from them? We think stars need to form in giant molecular clouds, but why wouldn't the clouds be shredded by the SMBH? I don't know if that's been resolved yet.
    I wonder if the s stars are actually derived from the g class remnants, stripped of their clouds and kicked out into a further orbit. Then where do the binary systems that form the g clouds come from; attracted in from the surrounding galaxy?

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    Quote Originally Posted by Ken G View Post
    I presume all those stars will eventually fall in, or there'd be a lot more of them orbiting by now.
    I can imagine a form of negative feedback in the dynamics.

    The more G objects collecting means more friction and more collisions, resulting in mass falling in - until the number of objects drops, resulting in an abatement of friction and collision.

    But the period of pseudo-stability could be arbitrarily long. Maybe there is a maximum number of G objects sustained, until occasionally one or two new objects drop a stellar monkey wrench into the works.

    Quote Originally Posted by Ken G View Post
    ... how did they form in an environment that is trying to rip off shells from them? We think stars need to form in giant molecular clouds, but why wouldn't the clouds be shredded by the SMBH?
    Well, all that mass is still there, even if it is on the slope of a gravity well. There's still going to be huge pressure waves and pressures and collapsing mass. When it rises out the well it its apoapsis, it could be enthusiastically regenerating.

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