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Is Our Solar System's Ninth Planet Actually a Primordial Black Hole? (forbes.com) 165

Posted by EditorDavid from the black-holes-matter dept.
An anonymous reader quotes Forbes: Conventional theory has it that Planet 9 — our outer solar system's hypothetical 9th planet — is merely a heretofore undetected planet, likely captured by our solar system at some point over its 4.6 billion year history. But Harvard University astronomers now raise the possibility that orbital evidence for Planet 9 could possibly be the result of a missing link in the decades-long puzzle of dark matter. That is, a hypothetical primordial black hole with a horizon size no larger than a grapefruit, and with a mass 5 to 10 times that of Earth.

In a paper accepted for publication in The Astrophysical Journal Letters, the co-authors argue that observed clustering of extreme trans-Neptunian objects suggest some sort of massive super-earth type body lying on the outer fringes of our solar system. Perhaps as much as 800 astronomical units (Earth-Sun distances) out...

If they exist, such primordial black holes would require new physics and go a long way towards solving the mystery of the universe's missing mass, or dark matter.
Their argument also constitutes a "new method to search for black holes in the outer solar system based on flares that result from the disruption of intercepted comets," according to a statement from the Harvard-Smithsonian Center for Astrophysics. The paper was co-authored by Avi Loeb, chair of Harvard's astronomy department, who points out that "Because black holes are intrinsically dark, the radiation that matter emits on its way to the mouth of the black hole is our only way to illuminate this dark environment."

And in an explanatory video, Mike Brown, a planetary astronomy professor at CalTech, suggests another way it could be significant. "All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found."
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Is Our Solar System's Ninth Planet Actually a Primordial Black Hole? More

Is Our Solar System's Ninth Planet Actually a Primordial Black Hole?

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  • Dwarf planet (Score:3, Interesting)

    by impaledsunset ( 1337701 ) on Sunday July 12, 2020 @03:40AM (#60288670)

    There wouldn't be any ninth planet, as such a body would be a dwarf planet!

    Look, son, a planet is a solar system body that needs to have cleared its neighbourhood. That be virtually impossible at the proposed orbits even for a gas giant-sized body.

    Look, you don't go all the way in introducing a half-cooked* definition just to disqualify Pluto as a planet as it didn't look like one to you just because you thought excluding it explicitly would feel arbitrary, and then immediately ignore your own definition when a thing that looks a planet to you becomes possible to exist.

    * The definition doesn't even account for extra-solar planets, as it requires planets to orbit the Sun.

    • Re: Dwarf planet (Score:2, Informative)

      by NagrothAgain ( 4130865 )
      The whole "cleared its orbit" thing is a bunch of nonsense which relies on a bunch of arbitrary definitions.

    • Re:Dwarf planet (Score:5, Interesting)

      by Solandri ( 704621 ) on Sunday July 12, 2020 @01:04PM (#60290290)
      The "half-cooked definition" wasn't to disqualify Pluto. It was to prevent textbooks from having to be rewritten every time a new trans-Neptunian object [wikipedia.org] was discovered and had to be added as a new planet. It wasn't that big a deal in 1930 when Pluto was discovered and people thought there were just a handful of large objects out there. But since then, the Oort cloud [wikipedia.org] theory has gained acceptance, which would mean there are thousands if not millions of such large objects orbiting far out there.

      Unfortunately for Pluto, its characteristics match more closely with these trans-Neptunian objects than it does the classic planets. So it was demoted.

      • Then the definition needed to be "Objects with the following physical characteristics: [list goes here] or for which a historical precedent exists to call them planets."

        It's as simple as that. No danger of textbooks needing to be overwritten. No need to demote Pluto.

    • There wouldn't be any ninth planet, as such a body would be a dwarf planet!

      If it is a Black Hole then it is not a planet at all since will have formed by a completely different mechanism and will have radically different properties. Indeed, I really hope it is a Black Hole since, with it being in the Solar System, it will be near enough to send a probe to. This will allow us to confirm things like Hawking Radiation but perhaps also so start refining models of Quantum Gravity far, far sooner than anyone has ever though possible.

  • Magic physics solves problem? No. (Score:4, Interesting)

    by Way Smarter Than You ( 6157664 ) on Sunday July 12, 2020 @03:51AM (#60288682)

    This was interesting until they noted the size which current physics says is too small to be a black hole. Then they doubled down and said "well yeah we know but wouldn't it be super cool if there were some totally new physical laws of magical gravity and mass we could make up so we can get more funding next year?"

    • Re: (Score:2, Informative)

      by Anonymous Coward

      Yeah, it's almost as if scientific endeavour starts out with speculative theories and then looks for funding to try and prove or disprove them to advance humanity or something.

      You're not even Way Smarter Than a Broken Dildo, let alone any actual human.

    • There is nothing about an earth mass black hole, or thereabouts, that violates physics or requires new physics. The lifetime of one is highly stable, over 10^67 years before it evaporates if Hawking radiation is correct so if it formed right at the Big Bang it would have not lost any measurable mass yet. The only “new physics” is understanding exactly what happened in that first 10^-30 second which is actually an area of ongoing research and is poorly understood. Small black holes (under abou

      • Re:Magic physics solves problem? No. (Score:5, Interesting)

        by hankwang ( 413283 ) on Sunday July 12, 2020 @08:12AM (#60289276) Homepage

        There is nothing about an earth mass black hole, or thereabouts, that violates physics or requires new physics.

        The thing is, other than "maybe many of them were formed during the big bang and survived billions of years without getting noticed before", there is no mechanism how one of them could be created.

        We know how neutron stars and black holes can be formed from large stars. There is no plausible mechanism for compressing a few earths worth of matter into the volume of a grapefruit. And wouldn't even a small black hole collect some interstellar gas into a mini-accretion disc that would render it visible?

        • Re: (Score:3)

          by ceoyoyo ( 59147 )

          And wouldn't even a small black hole collect some interstellar gas into a mini-accretion disc that would render it visible?

          No more than Neptune has collected a detectable accretion disk.

          • Well, Neptune doesn't have a surface gravity acceleration of 10^15 m/s^2 either. I don't know how close a particle needs to get to the Schwartzschild radius in order not to escape anymore, due to the non-conservative gravitational potential under relativistic conditions and due to radiation losses, nor how much radiation they would emit before they are swallowed. But I'd estimate that there can easily be 10^9 molecules per second per square meter (10^6 per m^3 density, 1 km/s velocity); it's not obvious to

            • Miniature black holes on the order of a hundred trillion metric tons don’t radiate hardly anything from Hawking radiation, are stable and would last since the Big Bang, have a size of only .1 nanometers, and wouldn’t likely be able to radiate much even if passing through solid matter. Much smaller and they start resembling massive explosions and are not stable on long timeframes, much larger and they would definitely radiate if they came in close contact with material of any kind.

            • Re: (Score:2)

              by ceoyoyo ( 59147 )

              Particles falling into the black hole don't radiate. Accretion disk radiation is X-rays from friction between particles in the disk. That depends a great deal on the size, speed and density of the disk. There isn't much stuff out that far, and a few Earth masses isn't that much gravity to capture and hold onto what stuff there is.

              The paper's authors do suggest searching for a low mass primordial black hole using x-ray emission, but x-rays from a dark matter halo that they expect would gather around primord

              • The problem is there needs to be 5x the dark matter as normal matter. If it were in earth massed black holes, there would be (lots and lots)^lots of interaction with normal matter, radiation when passing through gas clouds, we could see mergers with gravitational wave detectors etc. if it were in hundred trillion metric ton massed holes, they are still to large to radiate much Hawking radiation, are 0.1 nanometers in size, are too small to likely merge and if they do are too weak to detect unless they ar

                • Re: (Score:2)

                  by ceoyoyo ( 59147 )

                  I don't think I really followed what you're trying to say. The idea in the paper is that primordial black holes, which form in a very dense (matter and dark matter) universe, would hold onto their own little halo of dark matter. Not *in* the hole, around it. That over density of dark matter might be detectable because it would produce a very specific frequency of x-ray when it annihilated. If it annihilates.

                  That is certainly lots of assumptions and is unlikely to work.

                  • I was pointing out how larger primordial black holes can’t be that common or we would see the evidence for them. For example, having a large amount of earth mass black holes in the early universe would make a massive difference in how gas clouds collapse.

            • It doesn't matter if they're completely invisible or not.

              We're barely at the stage of indirectly observing large planets around other stars. It's very likely that the methodology we use to detect planets around other stars would exclude attempts at observing a similar mass black hole.

              A lot of the planet detection relies on watching the brightness of nearby stars dip like 1% on a regular basis as the planet occludes the star. Even if a primordial black hole had a ring, it likely wouldn't trigger the algorith

              • It’s easy to detect. Just wait about 10^70 years and look for a giant explosion.

              • Even hubble is going to struggle to find a hypothetical grapfruit with a ring that far out.

                Yeah, we're not going to find it visually. We'll have to find it by it's gravitational effects, I think. I'm not even sure if you could send a probe to look for it in the neighborhood it's supposed to be in and be able to 'see' anything, not if it's as small as they're saying it could be. It's not going to have a bunch of junk orbiting it, not if it's that small. Detect tidal effects from it, maybe?

        • The whole idea is that PBH aren't "created" from ordinary matter. They are areas where mass was so dense it collapsed into a black hole, before things like atoms and subatomic particles existed. Accretion disks eventually get pulled into the black hole. So, many black holes are invisible in EM terms.

        • wrong, there are plausible mechanisms in the early universe and Hawking wrote paper on it.

        • What many of you commenting on this subject aren't realizing is that the physics required to form such a tiny singularity only existed for a very short time at the very beginning of the Universe, during the Big Bang; those conditions do not exist anymore however. That's the theory anyway.

    • Re:Magic physics solves problem? No. (Score:4, Interesting)

      by ceoyoyo ( 59147 ) on Sunday July 12, 2020 @09:13AM (#60289454)

      What? There's no minimum size for a black hole. The only issue with small ones is explaining how they formed. Primordial black holes have been a popular explanation for the existence of small black holes for quite a while, because they probably should have formed in the early universe. The only "new physics" required would be to explain how they could make up a substantial portion of dark matter.

      • The only "new physics" required would be to explain how they could make up a substantial portion of dark matter.

        I suppose the thinking would be "there were many many of them formed at the same time"? And, if they're stable, they survived all these billions of years? And, if there's a 'grapefruit sized' one hanging around our local neighborhood, it got that way by clearing out random junk, increasing it's mass and size?

        • Re: (Score:2)

          by ceoyoyo ( 59147 )

          There are a bunch of observations that put limits on the number of black holes in specific size ranges. They don't seem to collide with neutron stars, white dwarfs or regular stars, microlensing searches, etc. I think there's still a bit of room for a significant fraction of dark matter to be primordial black holes, but it doesn't look very likely under our current understanding of the early universe.

    • This is Gravity 2.0 - twice as strong!
    • He can't even be bothered to read a Wikipedia article before opening his mouth

    • Re: (Score:2)

      by rtb61 ( 674572 )

      The only likely missing out there would be the left overs from the impact of Venus to give it it's contra orbit, distinct surface formations and screwed up atmosphere. It would be interesting to calculate the original orbits for Venus based upon that impact sufficient to alter it rotation and what the model of the solar system was like prior to that. Also why Mars has two distinct surfaces, like one was added long after it was formed.

      The only thing out there would be impact debris there nature dependent up

  • Glad to clear that up for you.

    • Re:No, it isn't. (Score:5, Insightful)

      by Sesostris III ( 730910 ) on Sunday July 12, 2020 @06:23AM (#60289050)
      It's a hypothesis. They have given a way that it can be tested. Now comes the testing part. That's how science progresses. Just saying 'No' to any new possible hypothesis isn't really science.

      • Re: (Score:2)

        by Calydor ( 739835 )

        How about we just launch a probe and aim it at where this supposed tiny black hole is going to be? It'll take what, 25-30 years to get out there, but at least we'll see if the probe suddenly gets gobbled up by something invisible.

  • Two possibilities (Score:5, Funny)

    by thegarbz ( 1787294 ) on Sunday July 12, 2020 @04:07AM (#60288710)

    1) Space is large and it's really really hard to find something orbiting 100 billion km out.
    2) It's a micro black hole hitherto-fore unexplained by physics.

    Yep we're going with number 2 because Occam's Razor isn't a thing.

  • If it's a primordial black hole (Score:3)

    by Antique Geekmeister ( 740220 ) on Sunday July 12, 2020 @05:55AM (#60289006)

    It establishes that they exist and that they're common enough to be found in our solar system. How common are they? If they're common enough for a large percentage of stars to have collected them, and they're also distributed remotely evenly in intergalactic space, then they're a comprehensible source of so-called "dark matter" with no new physics involved. Note also that primordial black holes do _not_ involve new principles of physics, simply a previously described of the Big Bang that is very difficult to detect. The theory is more than 50 years old.

    • The problem is if they are on the size of earth mass and a grapefruit, as opposed to a few hundred trillion metric tons and a tenth of a nanometer in size. With the former, gas will accrete and it will have a visible signature if it feeds like solar mass black holes. If two of these collided nearby (because there are supposedly lots), we could detect it with a gravitational wave detector (hint we haven’t). If it is the latter, it’s too big to radiate detectable Hawking radiation, too weak an

      • Do you have any pointers to the models for "the size of Earth and a grapefruit"? I assume you mean a black hole the mass of the Earth.

        The likelihood of collisions is a fascinating problem, and very dependent on their density. Since they're so difficult to detect directly, their density is also a fascinating question.

        • Here is a handy Hawking radiation calculator that lets you play around with a not charged not spinning black hole. Real ones won’t have any real charge but do have copious amounts of spin, this effectively shrinks the horizon radius and other parameters somewhat, but since astronomy math is 3+3=10 it still gives a good approximation.

    • Re:If it's a primordial black hole (Score:5, Interesting)

      by crunchygranola ( 1954152 ) on Sunday July 12, 2020 @09:46AM (#60289578)

      ...then they're a comprehensible source of so-called "dark matter" with no new physics involved...

      Not really. The paper (which is here [arxiv.org], /. never gives usable links to papers) is only claiming that they might account for up 10% of the dark matter mass of the Milky Way Galactic Halo.

      There is at this point only a narrow (logarithmic) range of black hole masses that could be invoked to explain the 85% of the matter in the Universe that we cannot detect, but by its large scale gravitational effect. This range is from 10^13 to 10^16 tonnes at most. Any process in the early Universe that converted 85% of its mass into black holes in the narrow very small size range would absolutely be entirely new physics. Dark matter is real, we can measure its distribution in the Universe, and even in our galaxy, and it isn't made of anything that we currently know exists.

  • Please replace the words "black hole" into "deny hole", as done elsewhere [slashdot.org].
    • Considering such an object absorbs 100% of all light cast on it, you could call it a 'ultrablackhole' and it would be just as valid; if I'm wearing a shirt of the color #000000, can I not call it a 'black shirt'? If I'm wearing a shirt that's #FFFFFF, would you not call it a 'white shirt'?
      I know you're being funny/sarcastic, but at the end of the day I don't think we can erase the entire concept of color from our language with regards to describing objects visual appearance, not without breaking our langua
  • Comment removed based on user account deletion
  • This sounds a bit like more mathematically-inclined people describing the old Nemesis hypothesis. https://en.wikipedia.org/wiki/... [wikipedia.org] I don't know offhand how far back this idea goes; I believe it was originally proposed to explain cyclic mass extinction events occurring due to bodies being upset in the outer reaches of the Solar System by a companion to our sun (maybe a brown dwarf, maybe a black hole, maybe something else) with an eccentric orbit shaking things up. I recall seeing a computer visualization
  • We've now examined thousands of planetary systems by observing the gravitational interaction of the star and the "dark stuff" (presumed to be planets) orbiting it. (We can watch the star wobble periodically as it orbits the system's center of mass, from which we can infer what else in the system has mass and how it's moving.) If primordial black holes with planet mass were common, this method would be a perfect way to detect them. But these little things wouldn't dim the star when they transit in front of i

    • No, not if orbit large, won't detect wobble.

      • also should have added, with say earth mass or more and 800 au distance orbital period would be 23,000 year.... not going to see transits very often, heh.

  • Highly elliptical orbits come close to the sun, so the mass can be tidally disrupted and one object can become many. (e.g. https://www.nature.com/article... [nature.com]) They can also be accelerated with each pass, (for instance this month's C/2020 F3 (NEOWISE) is leaving faster than it arrived) so that they are eventually ejected. The total mass in the orbit and the effects of that total mass could have still left the footprint we see on other solar system orbits.

    So there are two well known explanations for why p

  • Planet X theories have been around since 1906, [or Planet O in 1908 because O comes after (N)eptune] , to explain irregularities in the orbit of Uranus. However, once a more accurate mass for Neptune was obtained in 1993 the evidence for the existence of Planet X disappeared. Since Pluto was bumped to a snowball it's now Planet 9 that is heavy enough only to cause irregularities in outer solar system bodies, which we haven't proven the existence of.

    They are talking about hypothetical forms of a hypothetica

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