20 votes

‘Planet Nine’ may actually be a black hole

15 comments

  1. cmccabe
    Link
    Here’s a better article: https://gizmodo.com/what-if-planet-nine-is-a-bowling-ball-size-black-hole-1838527880 And the original paper: https://arxiv.org/pdf/1909.11090.pdf Unlike the sciencemag.org...

    Here’s a better article:
    https://gizmodo.com/what-if-planet-nine-is-a-bowling-ball-size-black-hole-1838527880

    And the original paper:
    https://arxiv.org/pdf/1909.11090.pdf

    Unlike the sciencemag.org article, this one emphasizes that the idea of Planet 9 as a primordial black hole is less literal and more intended to nudge astronomers into thinking more creatively about searching for the source of observed perturbations to the orbits of other planets.

    18 votes
  2. [12]
    KapteinB
    Link
    Can a black hole that small even exist? Why do they think it is surrounded by dark matter? Why would there also be dark antimatter in the halo?

    Can a black hole that small even exist?

    Why do they think it is surrounded by dark matter?

    Why would there also be dark antimatter in the halo?

    5 votes
    1. [11]
      Amarok
      Link Parent
      Black holes as we know them come from gravitational collapse, and the limit to their smallness from this process is thought to be around 1.5 solar masses, which is much more massive than this...
      • Exemplary

      Black holes as we know them come from gravitational collapse, and the limit to their smallness from this process is thought to be around 1.5 solar masses, which is much more massive than this hypothetical rogue black hole. That doesn't mean there aren't smaller black holes, though - we just don't know how one would go about creating a black hole smaller than 1.5 solar masses. It wouldn't come from typical stellar collapse at that size and there are no other models as far as I know.

      I've seen arguments that they could exist and even be stable at one Planck length, the smallest size there is in this universe. Micro black holes are also considered proof of extra dimensions for some theories. All of that stuff is hypothetical until we find one or create one in a lab. If memory serves the smallest we've ever seen in the wild is around 4 solar masses.

      Finding any black hole under 1.5 masses would be big news, and if we found one at five earth mass hiding in our own solar system - one we could visit, orbit, and study - that would be a stroke of luck for physics we'd never dare dream could be real. Unless it was towing a fleet of planet killing comets from the oort cloud in our direction, that is. It would be easier to find if that were the case. :P

      As for the dark matter, there's a curious relationship between black holes and dark matter and if we extrapolate from that we'd expect this shrimpy black hole to have the same sort of halo the rest of them do, and that might provide a mechanism for detection.

      Dark matter/anti-matter wants to be separated from itself. If you can imagine a universe where every single particle fights like hell to stay as far away as it can from every other particle, that's how dark matter is thought to behave. It's repulsive, not attractive. No molecules can form, so it's just raw primitive particle soup.

      That means gravity pulls these repulsive particles into large clouds orbiting massive objects, just like Saturn's rings but on a larger scale. Now imagine those rings pushing against each other and getting a lot larger/more disperse, but still unable to escape the gravity forcing them to become rings. We know this is real because we see the gravity of those dark particles distorting space time whenever we look at distant large objects though a telescope. Galaxies have gargantuan halos many times larger than the galaxy itself.

      Regular antimatter isn't long lived if it exists in nature - too much matter to collide with and poof, nothing but gamma rays left. We don't see it out there and we're always looking for it. Dark antimatter tries to avoid collisions and it doesn't interact with regular matter, so if it's out there still somewhere, it's in these halos with the regular dark matter, and it's got a much higher chance of still being around since it avoids collisions. Every once in a while, there could be a collision between dark matter/antimatter, and we'd expect to see gamma ray bursts come out of that, from apparently empty space. Pretty sure that's all still hypothetical as well.

      So, the short version is still - who knows? :P

      15 votes
      1. [4]
        imperialismus
        Link Parent
        Where did you get the idea that dark matter is repulsive? The whole reason we think dark matter exists is because we need unseen mass to explain how galaxies work. Which implies it must interact...

        Where did you get the idea that dark matter is repulsive? The whole reason we think dark matter exists is because we need unseen mass to explain how galaxies work. Which implies it must interact gravitationally like visible matter. And it must interact very weakly if at all electromagnetically, otherwise it wouldn't be dark matter - we'd be able to see it. What mysterious force would be responsible for this repulsive force? As far as I know, physicists do not believe that dark matter is repulsive to dark matter. Maybe you're getting it confused with dark energy?

        See these answers from physicists Ted Bunn and Lubos Motl. Bunn goes some way towards explaining why dark matter remains diffuse while still interacting in the ordinary way gravitationally (i.e. it attracts itself like regular matter):

        Lubos Motl's answer is exactly right. Dark matter has "ordinary" gravitational properties: it attracts other matter, and it attracts itself (i.e., each dark matter particle attracts each other one, as you'd expect).

        But it's true that dark matter doesn't seem to have collapsed into very dense structures -- that is, things like stars and planets. Dark matter does cluster, collapsing gravitationally into clumps, but those clumps are much larger and more diffuse than the clumps of ordinary matter we're so familiar with. Why not?

        The answer seems to be that dark matter has few ways to dissipate energy. Imagine that you have a diffuse cloud of stuff that starts to collapse under its own weight. If there's no way for it to dissipate its energy, it can't form a stable, dense structure. All the particles will fall in towards the center, but then they'll have so much kinetic energy that they'll pop right back out again. In order to collapse to a dense structure, things need the ability to "cool."

        Ordinary atomic matter has various ways of dissipating energy and cooling, such as emitting radiation, which allow it to collapse and not rebound. As far as we can tell, dark matter is weakly interacting: it doesn't emit or absorb radiation, and collisions between dark matter particles are rare. Since it's hard for it to cool, it doesn't form these structures.

        And here's part of Motl's answer, which also agrees that dark matter attracts dark matter:

        Dark matter surely has to carry a positive mass, and by the equivalence principle, all positive masses have to exert attractive gravity on other masses.

        Also, from the viewpoint of phenomenological cosmology, we obviously want dark matter to attract itself. It has to attract visible matter because this is why dark matter was introduced in the first place: it helps to keep the stars in a galaxy even though they're orbiting more quickly than one would expect from the distribution of visible mass in the galaxy.

        For this reason, the force between dark matter and ordinary is surely attractive. The force between dark matter and dark matter has to be attractive, too. In fact, dark matter has played the dominant role in the structure formation - the creation of the initial non-uniformities that ultimately became galaxies, clusters of galaxies, and so on. The dark matter halos are larger than the visible parts of the galaxies: the visible stars arose as "cherries on the pie" near the centers of the dark matter halos.

        5 votes
        1. [3]
          Amarok
          (edited )
          Link Parent
          I'm more partial to JS Farnes' theory from last year. Dark matter has negative mass, which is the source of the repulsive action. I'm well aware negative mass is regarded as heresy. I also find...

          I'm more partial to JS Farnes' theory from last year. Dark matter has negative mass, which is the source of the repulsive action.

          Dark energy and dark matter constitute 95% of the observable Universe. Yet the physical nature of these two phenomena remains a mystery. Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures. However, contemporary cosmological results are derived upon the reasonable assumption that the Universe only contains positive masses.

          By reconsidering this assumption, I have constructed a toy model which suggests that both dark phenomena can be unified into a single negative mass fluid. The model is a modified ΛCDM cosmology, and indicates that continuously-created negative masses can resemble the cosmological constant and can flatten the rotation curves of galaxies. The model leads to a cyclic universe with a time-variable Hubble parameter, potentially providing compatibility with the current tension that is emerging in cosmological measurements. In the first three-dimensional N-body simulations of negative mass matter in the scientific literature, this exotic material naturally forms haloes around galaxies that extend to several galactic radii. These haloes are not cuspy. The proposed cosmological model is therefore able to predict the observed distribution of dark matter in galaxies from first principles.

          The model makes several testable predictions and seems to have the potential to be consistent with observational evidence from distant supernovae, the cosmic microwave background, and galaxy clusters. These findings may imply that negative masses are a real and physical aspect of our Universe, or alternatively may imply the existence of a superseding theory that in some limit can be modeled by effective negative masses. Both cases lead to the surprising conclusion that the compelling puzzle of the dark Universe may have been due to a simple sign error.

          I'm well aware negative mass is regarded as heresy. I also find the paper's arguments that we should carefully reconsider this idea remarkably compelling. It makes plenty of testable predictions too, and CERN will likely have some answers to confirm this idea or rule it out within a couple of years.

          Edit: clarity/formatting

          4 votes
          1. imperialismus
            Link Parent
            In the future, maybe mention that you're talking about an extremely speculative theory that runs counter to mainstream physics. Your replies give the impression that you're talking about the...

            In the future, maybe mention that you're talking about an extremely speculative theory that runs counter to mainstream physics. Your replies give the impression that you're talking about the scientific consensus. That is what one tends to assume when no qualifications are present.

            3 votes
          2. SunSpotter
            Link Parent
            Really confused how this makes sense in the broader meaning of dark matter. The meaning being, a large collection of matter that can't be accounted for visually. We know that our galaxy is much...

            Really confused how this makes sense in the broader meaning of dark matter. The meaning being, a large collection of matter that can't be accounted for visually. We know that our galaxy is much more massive than it should be, accounting only for stars and interstellar gas, as one of the most famous examples. How would negative mass account for that? Wouldn't we observe our galaxy being less massive than it should be in that case?

            Also worth mentioning that your first two links don't actually seem to go anywhere for me, though I would be interested in reading them.

      2. [2]
        moocow1452
        Link Parent
        So this could totes be a wormhole that connects us to the greater culture of the universe for when we are ready to join the intergalactic community?

        So this could totes be a wormhole that connects us to the greater culture of the universe for when we are ready to join the intergalactic community?

        3 votes
        1. Amarok
          Link Parent
          Wormholes are still well outside the scope of our knowledge. If you want a fun rundown, I'll refer you to Issac Arthur's video on the subject.

          Wormholes are still well outside the scope of our knowledge. If you want a fun rundown, I'll refer you to Issac Arthur's video on the subject.

          2 votes
      3. KapteinB
        Link Parent
        Great explanation. Thanks!

        Great explanation. Thanks!

      4. [3]
        teaearlgraycold
        Link Parent
        Are you saying that dark matter and anti-matter are the same thing? I thought anti-matter was just normal matter with electrons/protons of opposite charges, and dark matter something completely...

        Dark matter/anti-matter wants to be separated from itself.

        Are you saying that dark matter and anti-matter are the same thing? I thought anti-matter was just normal matter with electrons/protons of opposite charges, and dark matter something completely different.

        If I misunderstand and you're just saying that anti-matter and dark matter both repel themselves, why would anti-matter do so but normal matter would not?

        1. [2]
          9000
          Link Parent
          I think they are saying that there are both normal and anti- versions of dark matter, just like normal matter, and both of these repel. Not that dark matter and anti-matter repel

          I think they are saying that there are both normal and anti- versions of dark matter, just like normal matter, and both of these repel. Not that dark matter and anti-matter repel

          5 votes
          1. Amarok
            (edited )
            Link Parent
            Yeah, I could have been clearer about that in my reply. We have (in theory) two classes, [matter / antimatter] and [dark matter / dark antimatter]. The regular kind attracts and forms into stuff...

            Yeah, I could have been clearer about that in my reply. We have (in theory) two classes, [matter / antimatter] and [dark matter / dark antimatter]. The regular kind attracts and forms into stuff like planets and people and stars, the dark kind refuses to get near itself so it never forms into anything. Both classes are unable to interact with each other outside of gravity.

            Physicists have been trying to figure out where the hell all the antimatter went (should be 50/50 according to theory) for a long time, it's one of the remaining big questions.

            It's worth noting that the dark stuff is the vast, vast super majority of all matter in the universe, and it moves slow compared to normal particles, which is what gets it trapped into these halos. It just gloms around normal matter in vast quantities due to gravity. You're swimming in it right now, you may as well be encased in a big puffy sponge made of the stuff. There's more info about it in this video. If that makes your head hurt, well, now you know how most astrophysicists have been feeling for the last decade as they try to puzzle out this strange mess.

            2 votes
  3. [2]
    cfabbro
    Link
    Although unrelated to this new black hole theory, Veritasium did a video on Planet Nine a few weeks ago that people might also find interesting: https://www.youtube.com/watch?v=pe83T9hISoY

    Although unrelated to this new black hole theory, Veritasium did a video on Planet Nine a few weeks ago that people might also find interesting: https://www.youtube.com/watch?v=pe83T9hISoY

    4 votes
    1. [2]
      Comment deleted by author
      Link Parent
      1. Thrabalen
        Link Parent
        Hey, a previous proposal was Xena. Bowie is a step up. That said, I'd love to see it named after Diana, the Roman equivalent to Artemis. A hunter, out in the wastes, being hunted herself by science.

        Hey, a previous proposal was Xena. Bowie is a step up.

        That said, I'd love to see it named after Diana, the Roman equivalent to Artemis. A hunter, out in the wastes, being hunted herself by science.

        9 votes