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I find one theory regarding Planet 9 especially interesting, and that is that it could be a primordial black hole with a Schwarzschild radius on the order of ju

I find one theory regarding Planet 9 especially interesting, and that is that it could be a primordial black hole with a Schwarzschild radius on the order of just a few centimeters. So basically, just a golf ball-sized black hole. This would explain why we can see the gravitational effects on the other objects as described in many papers, and it would also explain at the same time why we have no direct observation of this object, because it's simply too tiny and black.

api 1y ago
I really hope this is true, because it would mean there is a black hole close enough it could be examined and studied. This might allow us to test physics ideas that can’t be tested any other way, and maybe even to “finish” physics. It could also allow gravity and Oberth effect acceleration of small probes to meaningful fractions of the speed of light for interstellar flyby missions. Imagine the Oberth effect boost from thrusting in such a deep gravity well.
- TheOtherHobbes 1y ago
  I really hope it isn't true because if there's one out there, there will be others, and I'd rather not meet one in person. We don't have enough data to see whether there are unexpected instabilities in detected planetary systems. But it would be an interesting project to look for those.
  - api 1y ago
    They're not dangerous unless you get too close. A black hole is not a cosmic vacuum cleaner. If the Moon were suddenly transformed into a tiny black hole with the same mass, it would continue to orbit the Earth at the same distance. Ocean tides due to its gravity would continue normally. There would not be much effect except that it would no longer be visible with the naked eye and would no longer reflect the sun's light back to Earth. If you found it in a telescope, you might see gravitational lensing as it passed in front of the star field. Objects like probes or old spacecraft stages orbiting the Moon would continue to do so. The only danger would be that if things fell into it I suppose you might get dangerous X-ray and gamma ray emissions from its accretion disc that would be a problem at such a close range. That would not be an issue with a primordial black hole much further away. If there were such an object we could send probes to orbit it and study it, and some experiments may involve firing objects or shooting lasers or beams of particles into it to attempt to learn about the quantum effects at the event horizon. This could be massive for physics, allowing us to access and observe conditions and energies not replicable here on Earth with any current technology. BTW we don't have any hard evidence that primordial black holes exist, but many theories predict them. So far such predictions around black holes have a pretty good track record. If you made me bet, I would bet on them existing. They are a candidate for some or perhaps even all of dark matter, though even if that's not the case they might still exist. It's possible that the dark matter haloes we can spot with gravitational lensing are clouds of these things. ("Clouds" of course is a misnomer-- the distance between them would be many light years.) If planet nine is a PBH it means that at some point one was captured by our solar system into a Kuiper Belt orbit. Even if planet nine isn't one, there still may be small asteroid mass PBHs in our solar system, so we still might find one. They would require extremely sensitive X-ray or gamma ray telescopes or highly accurate gravitational models of the solar system to detect.
    - deleted 1y ago
      [deleted]
    - nonethewiser 1y ago
      That is very interesting and made me realize I did think of black holes as “sucking” things in. Which I see is not the right way to think about it.
      - api 1y ago
        It’s an object with theoretical maximum density. That’s one way to think about it. Another visualization: if you had an Earth mass black hole with a solid shell surrounding it at the same radius as the Earth’s surface is from its core, gravity atop that shell would be 1g. The actual black hole would be about the size of a marble. If you got close to it you would of course be subject to insane gravity and be “spaghettified” etc. All the mass would be in that marble. But at a distance it would be the same. Compared to that object the Earth is mostly empty space. Ordinary matter is not that dense. Black holes are totally fascinating. They are in some ways the most extreme objects that can possibly exist. If we could study one we could learn a lot.
        philipov 1y ago
        That's Newton's Shell Theorem for you.
        baxtr 1y ago
        I love HN for these kind of comments
        XorNot 1y ago
        They're also interestingly one of the most boring: every black hole can be described by 3 numbers: mass, spin and charge. Which is to say they are extremely high entropy.
        api 1y ago
        They are extremely high entropy as far as what's accessible. We don't know what's really on the inside.
  - shiandow 1y ago
    Running into a rogue black hole must be far less likely than an extinction level impact with a relstively boring big rock.
    - deleted 1y ago
      [deleted]
    - api 1y ago
      I recall reading years ago some speculation that the Tunguska event may have been an encounter with such an object. A micro black hole traveling at tremendous velocity would go right through the Earth and keep going, but as it encountered the atmosphere it might emit a bunch of ultra high energy gamma rays (due to accretion) that set off fusion reactions and create an airburst. From there it would shoot right through the Earth and cause another kaboom when it exited, but that would have been in the middle of the Pacific. Nobody would have noticed in 1908. https://en.wikipedia.org/wiki/Tunguska_event https://en.wikipedia.org/wiki/Tunguska_event No way of knowing unless we find evidence in the form of a "track" through layers of rock or some other signature. A comet or other similar body remains a more likely explanation for that event.
      - mock-possum 1y ago
        It’s a fun idea - I vaguely remember listening to an NPR show / podcast on the subject last year.
  - colonial 1y ago
    They're no more dangerous than a regular rogue planet, which are pretty common on a galactic scale. The gravitational effects (disruption to planetary orbits) are the same, and Earth would not meaningfully survive a collision with either.
- ednite 1y ago
  Honestly, if there is a golf ball–sized black hole out there chilling in the outer solar system, I'm all in. Let’s fire up a replica of TARS, load up ChatGPT inside (TARS-GPT, patent pending), and yeet it straight toward the Schwarzschild golf ball. It’ll narrate live. Imagine the livestream: “Approaching event horizon. Spaghettification at 3%. Mood: stretchy.” “Entering gravitational lensing zone… wow, even my tokens are redshifting.” Bonus: With the right timing and Oberth maneuver, TARS-GPT might sling itself into Alpha Centauri before we finish arguing whether Pluto’s a planet again. Worst case: we lose a robot. Best case: we unlock quantum gravity and get a podcast from inside a black hole. I'd call that a win.
  - ednite 1y ago
    Not sure why the downvotes—if I came off wrong, my apologies. I genuinely meant it in a humoristic way. I'd honestly love to see a probe launched into a black hole.
    - misnome 1y ago
      It’s the AI Poe’s law: Any joke is indistinguishable from insane stuff LLM advocates will earnestly say they can do.
    - snapetom 1y ago
      We don't do humor here, and I'm not kidding. Humor devolves the site into useless one liners. If you want evidence of that, go to reddit and see how useful that site is these days if you want to actually research and learn something. Slashdot knew this back in the day and while funny posts got visibility, they did not add anything to a user's total karma score.
      - ednite 1y ago
        Fair enough--I'll be more mindful next time. Thanks for letting me know.
      - vaxman 1y ago
        Oh this site does humor great, it's just that the serious participants are so "focused" they don't (or can't) realize how funny their often esoteric comments are. As far as devolving into useless one liners --there is an emerging tech called the at-proto (not related to modems hahaa) that is poised to disrupt billions of dollars worth of sites like this one. Enjoy this era while it lasts..
- kiba 1y ago
  We could use the black hole to power our civilization due to how efficient it is for generating power.
  - api 1y ago
    Not at that distance but black hole starship drives are theoretically possible. Far, far beyond our capabilities but possible within known physics. This is like Kardashev type II civilization stuff. Domesticating fusion would be much easier. That is within sight.
  - ta1243 1y ago
    No need for something that exotic. The Earth alone receives more energy from the sun every hour than mankind uses each year.
    - john2x 1y ago
      Yeah but you can't raise trillions of dollars with that. Investors want to be able to tell to their friends at parties that they helped made blackhole tech possible.
- zveyaeyv3sfye 1y ago
  Not sure I want a black hole in my backyard ;-) For all it's worth, there's no need to go black hole to explain the lack of visual observation. Objects that far from a star reflect very little if any light and would appear black to a black background.
  - margalabargala 1y ago
    Black holes are no more "dangerous" than other objects of equal mass. If a black hole with a mass of, say, Ceres hit the Earth, it would not be particularly worse than if Ceres hit the Earth.
    - devoutsalsa 1y ago
      I’d love see a mini-Ceres about this streaming on Nebula.
      - andrekandre 1y ago
        cerial storytelling ftw ^^
    - magicalist 1y ago
      > If a black hole with a mass of, say, Ceres hit the Earth, it would not be particularly worse than if Ceres hit the Earth. This equivalency is true for many aspects of orbital mechanics (depending on setup giving sufficient distance), but I don't believe that's true at all for a collision. Someone with more knowledge correct me, but a black hole with the mass of Ceres would be very tiny but also emitting a ton of radiation. The collision would be very different.
      - margalabargala 1y ago
        I more mean that the resulting moon-sized fragments of what used to be the earth would be equally devoid of life. I agree the physics might vary somewhat. If the black hole had a mass more similar to a 0.5-mile asteroid...well, I'm not sure what would happen. Would it just punch a hole straight through the earth?
ajross 1y ago
FWIW, the object in the linked article is visible, so while that's an interesting theory it's actually ruled out if this thing turns out to be a planet. The black hole would need to be Planet 10 I guess.
lazide 1y ago
At the distances described, available passive light flux is so low, it could be 100% painted with white titanium dioxide paint and we’d be lucky to ever see it. It doesn’t need to be a black hole to be effectively invisible.
- perihelions 1y ago
  Indeed, it's a doubly inverse-squared law: one 1/d^2 factor for how far it is from the sun, by how much the solar flux is reduced; and one 1/d^2 factor again for how it is from Earth-based observers. 1/d^4, a quartic law. That's the idea behind this paper (and similar ones like it): since they're looking for the planet's intrinsic emissions, from its internal heat, it's only a single inverse-square law. With d being ~20 times Neptune's distance and ~140 times Jupiter's, these really are large factors!
Projectiboga 1y ago
If it were earth mass it would be ~grapefruit size. This estimate puts object nine at 9 earth mass so maybe vollyball size or melon size? https://www.astronomy.com/science/is-planet-nine-a-black-hole-or-a-planet-harvard-scientists-suggest-a-way-to-find-out/ https://www.astronomy.com/science/is-planet-nine-a-black-hol...
- tlogan 1y ago
  If I’m remembering right, compressing all of Earth’s mass would give a Schwarzschild radius of roughly 9 mm. I think Uranus (15x heavier than earth) would be like basketball. Is my calculation correct?
- Qem 1y ago
  If it were a blackhole it wouldn't show up in IRAS and AKARI infrared maps.
  - tremon 1y ago
    Wait, are you saying we have infrared maps showing planet 9?
    - IAmGraydon 1y ago
      For god's sake man read the article before you comment.
  - bobmcnamara 1y ago
    Would probably be a screamer on x-ray though.
    - XorNot 1y ago
      Not without an accretion disk, and why would it have one? It would've cleared it's orbit.
      - bobmcnamara 1y ago
deadbabe 1y ago
Any chance we could use this black hole as a really powerful slingshot by getting very close right before passing the event horizon and then firing off into space?
- randomtoast 1y ago
  I think one problem for such tiny black holes is the way the gravitation works on objects that come close to it. So for instance, a spaceship could or a human could not reach the event horizon of a tiny black hole in one piece, because it would be torn apart by the gravitational tides. So the question is how close can you come to the event horizon before gravitation rips you apart. My guesstimation would be not close enough to reach a meaningful percentage of c.
interludead 1y ago
A golf ball–sized primordial black hole lurking in the outer solar system sounds like pure sci-fi, but it would neatly explain the gravitational weirdness and the lack of visual detection
goku12 1y ago
It would be extremely difficult to observe something that far away from the sun, no matter how voluminous it is. I'm not going to scorn at the idea of a blackhole, but I wonder what process can crush that much mass into such a volume. I don't think it's massive enough to suffer a gravitational collapse.
- smolder 1y ago
  Primordial black holes can theoretically be much smaller than those formed in the usual way from collapsed stars or neutron star mergers, etc, because the early universe was dense with matter already and perturbations could have caused gravitational collapses for arbitrary volumes. I don't think we've observed any directly, which would be hard as small low-emission masses. They're still a potential piece of the dark matter missing-mass puzzle.
- yfontana 1y ago
  Primordial black holes are black holes that formed right after the big bang. Basically areas where gravity caused the extremely dense matter of the universe's first instants to collapse into black holes before expansion could pull it apart. Their existence has been hypothesized but not confirmed (or definitively rejected) so far.
snowwrestler 1y ago
This paper exploring the idea has as Fig 1. a to-scale illustration of a 5-Earth-mass primordial black hole: https://arxiv.org/pdf/1909.11090 https://arxiv.org/pdf/1909.11090 As I recall, it did not get printed this way because the ink would be too expensive, or mess with the paper.

api 1y ago

I really hope this is true, because it would mean there is a black hole close enough it could be examined and studied. This might allow us to test physics ideas that can’t be tested any other way, and maybe even to “finish” physics. It could also allow gravity and Oberth effect acceleration of small probes to meaningful fractions of the speed of light for interstellar flyby missions. Imagine the Oberth effect boost from thrusting in such a deep gravity well.

TheOtherHobbes 1y ago
I really hope it isn't true because if there's one out there, there will be others, and I'd rather not meet one in person. We don't have enough data to see whether there are unexpected instabilities in detected planetary systems. But it would be an interesting project to look for those.
- api 1y ago
  They're not dangerous unless you get too close. A black hole is not a cosmic vacuum cleaner. If the Moon were suddenly transformed into a tiny black hole with the same mass, it would continue to orbit the Earth at the same distance. Ocean tides due to its gravity would continue normally. There would not be much effect except that it would no longer be visible with the naked eye and would no longer reflect the sun's light back to Earth. If you found it in a telescope, you might see gravitational lensing as it passed in front of the star field. Objects like probes or old spacecraft stages orbiting the Moon would continue to do so. The only danger would be that if things fell into it I suppose you might get dangerous X-ray and gamma ray emissions from its accretion disc that would be a problem at such a close range. That would not be an issue with a primordial black hole much further away. If there were such an object we could send probes to orbit it and study it, and some experiments may involve firing objects or shooting lasers or beams of particles into it to attempt to learn about the quantum effects at the event horizon. This could be massive for physics, allowing us to access and observe conditions and energies not replicable here on Earth with any current technology. BTW we don't have any hard evidence that primordial black holes exist, but many theories predict them. So far such predictions around black holes have a pretty good track record. If you made me bet, I would bet on them existing. They are a candidate for some or perhaps even all of dark matter, though even if that's not the case they might still exist. It's possible that the dark matter haloes we can spot with gravitational lensing are clouds of these things. ("Clouds" of course is a misnomer-- the distance between them would be many light years.) If planet nine is a PBH it means that at some point one was captured by our solar system into a Kuiper Belt orbit. Even if planet nine isn't one, there still may be small asteroid mass PBHs in our solar system, so we still might find one. They would require extremely sensitive X-ray or gamma ray telescopes or highly accurate gravitational models of the solar system to detect.
  - deleted 1y ago
    [deleted]
  - nonethewiser 1y ago
    That is very interesting and made me realize I did think of black holes as “sucking” things in. Which I see is not the right way to think about it.
    - api 1y ago
      It’s an object with theoretical maximum density. That’s one way to think about it. Another visualization: if you had an Earth mass black hole with a solid shell surrounding it at the same radius as the Earth’s surface is from its core, gravity atop that shell would be 1g. The actual black hole would be about the size of a marble. If you got close to it you would of course be subject to insane gravity and be “spaghettified” etc. All the mass would be in that marble. But at a distance it would be the same. Compared to that object the Earth is mostly empty space. Ordinary matter is not that dense. Black holes are totally fascinating. They are in some ways the most extreme objects that can possibly exist. If we could study one we could learn a lot.
      - philipov 1y ago
        That's Newton's Shell Theorem for you.
      - baxtr 1y ago
        I love HN for these kind of comments
      - XorNot 1y ago
        They're also interestingly one of the most boring: every black hole can be described by 3 numbers: mass, spin and charge. Which is to say they are extremely high entropy.
        api 1y ago
        They are extremely high entropy as far as what's accessible. We don't know what's really on the inside.
- shiandow 1y ago
  Running into a rogue black hole must be far less likely than an extinction level impact with a relstively boring big rock.
  - deleted 1y ago
    [deleted]
  - api 1y ago
    I recall reading years ago some speculation that the Tunguska event may have been an encounter with such an object. A micro black hole traveling at tremendous velocity would go right through the Earth and keep going, but as it encountered the atmosphere it might emit a bunch of ultra high energy gamma rays (due to accretion) that set off fusion reactions and create an airburst. From there it would shoot right through the Earth and cause another kaboom when it exited, but that would have been in the middle of the Pacific. Nobody would have noticed in 1908. https://en.wikipedia.org/wiki/Tunguska_event https://en.wikipedia.org/wiki/Tunguska_event No way of knowing unless we find evidence in the form of a "track" through layers of rock or some other signature. A comet or other similar body remains a more likely explanation for that event.
    - mock-possum 1y ago
      It’s a fun idea - I vaguely remember listening to an NPR show / podcast on the subject last year.
- colonial 1y ago
  They're no more dangerous than a regular rogue planet, which are pretty common on a galactic scale. The gravitational effects (disruption to planetary orbits) are the same, and Earth would not meaningfully survive a collision with either.
ednite 1y ago
Honestly, if there is a golf ball–sized black hole out there chilling in the outer solar system, I'm all in. Let’s fire up a replica of TARS, load up ChatGPT inside (TARS-GPT, patent pending), and yeet it straight toward the Schwarzschild golf ball. It’ll narrate live. Imagine the livestream: “Approaching event horizon. Spaghettification at 3%. Mood: stretchy.” “Entering gravitational lensing zone… wow, even my tokens are redshifting.” Bonus: With the right timing and Oberth maneuver, TARS-GPT might sling itself into Alpha Centauri before we finish arguing whether Pluto’s a planet again. Worst case: we lose a robot. Best case: we unlock quantum gravity and get a podcast from inside a black hole. I'd call that a win.
- ednite 1y ago
  Not sure why the downvotes—if I came off wrong, my apologies. I genuinely meant it in a humoristic way. I'd honestly love to see a probe launched into a black hole.
  - misnome 1y ago
    It’s the AI Poe’s law: Any joke is indistinguishable from insane stuff LLM advocates will earnestly say they can do.
  - snapetom 1y ago
    We don't do humor here, and I'm not kidding. Humor devolves the site into useless one liners. If you want evidence of that, go to reddit and see how useful that site is these days if you want to actually research and learn something. Slashdot knew this back in the day and while funny posts got visibility, they did not add anything to a user's total karma score.
    - ednite 1y ago
      Fair enough--I'll be more mindful next time. Thanks for letting me know.
    - vaxman 1y ago
      Oh this site does humor great, it's just that the serious participants are so "focused" they don't (or can't) realize how funny their often esoteric comments are. As far as devolving into useless one liners --there is an emerging tech called the at-proto (not related to modems hahaa) that is poised to disrupt billions of dollars worth of sites like this one. Enjoy this era while it lasts..
kiba 1y ago
We could use the black hole to power our civilization due to how efficient it is for generating power.
- api 1y ago
  Not at that distance but black hole starship drives are theoretically possible. Far, far beyond our capabilities but possible within known physics. This is like Kardashev type II civilization stuff. Domesticating fusion would be much easier. That is within sight.
- ta1243 1y ago
  No need for something that exotic. The Earth alone receives more energy from the sun every hour than mankind uses each year.
  - john2x 1y ago
    Yeah but you can't raise trillions of dollars with that. Investors want to be able to tell to their friends at parties that they helped made blackhole tech possible.
zveyaeyv3sfye 1y ago
Not sure I want a black hole in my backyard ;-) For all it's worth, there's no need to go black hole to explain the lack of visual observation. Objects that far from a star reflect very little if any light and would appear black to a black background.
- margalabargala 1y ago
  Black holes are no more "dangerous" than other objects of equal mass. If a black hole with a mass of, say, Ceres hit the Earth, it would not be particularly worse than if Ceres hit the Earth.
  - devoutsalsa 1y ago
    I’d love see a mini-Ceres about this streaming on Nebula.
    - andrekandre 1y ago
      cerial storytelling ftw ^^
  - magicalist 1y ago
    > If a black hole with a mass of, say, Ceres hit the Earth, it would not be particularly worse than if Ceres hit the Earth. This equivalency is true for many aspects of orbital mechanics (depending on setup giving sufficient distance), but I don't believe that's true at all for a collision. Someone with more knowledge correct me, but a black hole with the mass of Ceres would be very tiny but also emitting a ton of radiation. The collision would be very different.
    - margalabargala 1y ago
      I more mean that the resulting moon-sized fragments of what used to be the earth would be equally devoid of life. I agree the physics might vary somewhat. If the black hole had a mass more similar to a 0.5-mile asteroid...well, I'm not sure what would happen. Would it just punch a hole straight through the earth?

ajross 1y ago

FWIW, the object in the linked article is visible, so while that's an interesting theory it's actually ruled out if this thing turns out to be a planet. The black hole would need to be Planet 10 I guess.

lazide 1y ago

At the distances described, available passive light flux is so low, it could be 100% painted with white titanium dioxide paint and we’d be lucky to ever see it. It doesn’t need to be a black hole to be effectively invisible.

perihelions 1y ago
Indeed, it's a doubly inverse-squared law: one 1/d^2 factor for how far it is from the sun, by how much the solar flux is reduced; and one 1/d^2 factor again for how it is from Earth-based observers. 1/d^4, a quartic law. That's the idea behind this paper (and similar ones like it): since they're looking for the planet's intrinsic emissions, from its internal heat, it's only a single inverse-square law. With d being ~20 times Neptune's distance and ~140 times Jupiter's, these really are large factors!

Projectiboga 1y ago

If it were earth mass it would be ~grapefruit size. This estimate puts object nine at 9 earth mass so maybe vollyball size or melon size? https://www.astronomy.com/science/is-planet-nine-a-black-hole-or-a-planet-harvard-scientists-suggest-a-way-to-find-out/ https://www.astronomy.com/science/is-planet-nine-a-black-hol...

tlogan 1y ago
If I’m remembering right, compressing all of Earth’s mass would give a Schwarzschild radius of roughly 9 mm. I think Uranus (15x heavier than earth) would be like basketball. Is my calculation correct?
Qem 1y ago
If it were a blackhole it wouldn't show up in IRAS and AKARI infrared maps.
- tremon 1y ago
  Wait, are you saying we have infrared maps showing planet 9?
  - IAmGraydon 1y ago
    For god's sake man read the article before you comment.
- bobmcnamara 1y ago
  Would probably be a screamer on x-ray though.
  - XorNot 1y ago
    Not without an accretion disk, and why would it have one? It would've cleared it's orbit.
    - bobmcnamara 1y ago

deadbabe 1y ago

Any chance we could use this black hole as a really powerful slingshot by getting very close right before passing the event horizon and then firing off into space?

randomtoast 1y ago
I think one problem for such tiny black holes is the way the gravitation works on objects that come close to it. So for instance, a spaceship could or a human could not reach the event horizon of a tiny black hole in one piece, because it would be torn apart by the gravitational tides. So the question is how close can you come to the event horizon before gravitation rips you apart. My guesstimation would be not close enough to reach a meaningful percentage of c.

interludead 1y ago

A golf ball–sized primordial black hole lurking in the outer solar system sounds like pure sci-fi, but it would neatly explain the gravitational weirdness and the lack of visual detection

goku12 1y ago

It would be extremely difficult to observe something that far away from the sun, no matter how voluminous it is. I'm not going to scorn at the idea of a blackhole, but I wonder what process can crush that much mass into such a volume. I don't think it's massive enough to suffer a gravitational collapse.

smolder 1y ago
Primordial black holes can theoretically be much smaller than those formed in the usual way from collapsed stars or neutron star mergers, etc, because the early universe was dense with matter already and perturbations could have caused gravitational collapses for arbitrary volumes. I don't think we've observed any directly, which would be hard as small low-emission masses. They're still a potential piece of the dark matter missing-mass puzzle.
yfontana 1y ago
Primordial black holes are black holes that formed right after the big bang. Basically areas where gravity caused the extremely dense matter of the universe's first instants to collapse into black holes before expansion could pull it apart. Their existence has been hypothesized but not confirmed (or definitively rejected) so far.

snowwrestler 1y ago

This paper exploring the idea has as Fig 1. a to-scale illustration of a 5-Earth-mass primordial black hole: https://arxiv.org/pdf/1909.11090 https://arxiv.org/pdf/1909.11090 As I recall, it did not get printed this way because the ink would be too expensive, or mess with the paper.