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" But the history of astronomy is rife with speculation that is never borne out: The same guy who correctly predicted the existence of Neptune also believed tha

by FuNe 10y ago

" But the history of astronomy is rife with speculation that is never borne out: The same guy who correctly predicted the existence of Neptune also believed that a planet he called Vulcan was responsible for the wobble of Mercury. That “discovery” caused the astronomy world to waste years looking for something that wasn't there. (Mercury's wobble was eventually explained by the theory of general relativity.) " Buying into the theory though and given that there is no sight of it yet - has the possibility of a small black hole been considered?

nickff 10y ago
Depending on when exactly you think the black hole was formed, it would likely have grown large enough to swallow the rest of the solar system. Simply swallowing interplanetary particles would cause fairly quick growth, and the black hole would soon be absorbing comets and asteroids; in addition, it would obscure and distort our view of distant stars. Apart from those issues which would make the black hole apparent, you would have to figure out how one could form in a stable solar system. I am not aware of any theory of black holes which would explain how one could spontaneously form within a stable solar system.
- FuNe 10y ago
  Could be a mini stray back hole caught up in a highly elliptical orbit around our solar system (not much of interplanetary particles there - right) ? I have not studied astrophysics (quite obviously) - just pitching ideas.
  - zamalek 10y ago
    The more important thing here is that there is currently no reason to believe that it's a black hole - although it would be cool to have access to that sort of experiment.
- scatters 10y ago
  Such a black hole would have to be primordial, and then you'd have to explain how it came to be associated with our solar system. Far more likely that a planetary-mass object associated with a solar system is an actual planet. I don't think it'd be likely to accrete much mass, though; a back-of-the-envelope calculation of a 10 Earth mass black hole in the outer solar system subject to interstellar mass flux gives an accretion rate of 0.1 nanograms/year and a radiative power of 0.1 milliwatts. Likewise, its Schwarzschild radius would be of the order of 10cm, so gravitational lensing events would be nigh-on unobservable.
  - MichaelApproved 10y ago
    Speaking of primordial black holes, PBS Space Time had a recent episode where they covered this topic. https://www.youtube.com/watch?v=rcv_tYcRgw4 https://www.youtube.com/watch?v=rcv_tYcRgw4 The overall series is great with ~10 minute long videos that dives deep into spacetime topics while barely touching on actual equations.
  - Zardoz84 10y ago
    And how many Howkings radiation would have a black hole of these mass ?
    - scatters 10y ago
      I remember the rule of thumb is that a Moon-mass black hole is in equilibrium with the microwave background (in the current era). So such a planetary-mass black hole would be several times colder than the microwave background and would actually absorb energy.
  - raattgift 10y ago
    Yes, and if we just accept arguendo that such black holes exist in our universe (and in reality they have not been precluded, as I note below), we have a density problem, although the argument is pretty Copernican (or alternatively rests on the cosmological counting system: forbidden, exactly one, mandatory). One problem with the argument that there is just one in the solar system is that unless it's unique, we would expect to see effects on star motions on a large enough number of nearby stars that one has to be inventive in attempting to explain why we haven't notice that yet. Worse, you would expect that at least one PBH would be near each supernova, and would interact with remnants, and that does not appear to be the case. Additionally, even if there was one in essentially every star system in every galaxy, they're still a tiny fraction of the dark matter sector, and we'd have to work even harder on an explanation for the core-cusp problem. That said, ~ the high end of sublunar mass PBHs (~ 10^23 kg) is about the least constrained mass region, so it's not surprising that people speculate about ~ M_earth PBHs. "[H]ow it came to be associated with our solar system" is fairly straightforward -- the field of PBHs existed before large structure formation, so you have the question a little backwards. The PBH was here first and its perturbations of the pre-sun GMC would have influenced the formation of our solar system. The question is whether those perturbations conflict with reasonable hypotheses for the formation and evolution of the solar system (and its predecessor). And again, you would expect PBHs to be involved in most similar star systems, and get to wonder about the gradient of such tiny black holes from the centres of galaxies to space outside galactic clusters. (Extragalactic space inside galactic clusters is maybe worse: there's invisible mass-energy among the galaxies mixed in with dust and gas, so why aren't stars forming there if the density of small PBHs is roughly similar to the outer edges of galaxies within the clusters? And if the density is very different, then why?) Finally, https://arxiv.org/abs/1607.06077v3 https://arxiv.org/abs/1607.06077v3 is very fresh and lists some further relevant constraints, but leans especially on https://arxiv.org/abs/1301.4984 https://arxiv.org/abs/1301.4984 .
bmm6o 10y ago
> Mercury's wobble was eventually explained by the theory of general relativity So, explaining the observations only took an entire new branch of physics? Only in hindsight is "maybe we don't understand how things move through space" the more obvious explanation than "maybe there's something there we haven't seen".

by FuNe 10y ago

nickff 10y ago

Depending on when exactly you think the black hole was formed, it would likely have grown large enough to swallow the rest of the solar system. Simply swallowing interplanetary particles would cause fairly quick growth, and the black hole would soon be absorbing comets and asteroids; in addition, it would obscure and distort our view of distant stars. Apart from those issues which would make the black hole apparent, you would have to figure out how one could form in a stable solar system. I am not aware of any theory of black holes which would explain how one could spontaneously form within a stable solar system.

FuNe 10y ago
Could be a mini stray back hole caught up in a highly elliptical orbit around our solar system (not much of interplanetary particles there - right) ? I have not studied astrophysics (quite obviously) - just pitching ideas.
- zamalek 10y ago
  The more important thing here is that there is currently no reason to believe that it's a black hole - although it would be cool to have access to that sort of experiment.
scatters 10y ago
Such a black hole would have to be primordial, and then you'd have to explain how it came to be associated with our solar system. Far more likely that a planetary-mass object associated with a solar system is an actual planet. I don't think it'd be likely to accrete much mass, though; a back-of-the-envelope calculation of a 10 Earth mass black hole in the outer solar system subject to interstellar mass flux gives an accretion rate of 0.1 nanograms/year and a radiative power of 0.1 milliwatts. Likewise, its Schwarzschild radius would be of the order of 10cm, so gravitational lensing events would be nigh-on unobservable.
- MichaelApproved 10y ago
  Speaking of primordial black holes, PBS Space Time had a recent episode where they covered this topic. https://www.youtube.com/watch?v=rcv_tYcRgw4 https://www.youtube.com/watch?v=rcv_tYcRgw4 The overall series is great with ~10 minute long videos that dives deep into spacetime topics while barely touching on actual equations.
- Zardoz84 10y ago
  And how many Howkings radiation would have a black hole of these mass ?
  - scatters 10y ago
    I remember the rule of thumb is that a Moon-mass black hole is in equilibrium with the microwave background (in the current era). So such a planetary-mass black hole would be several times colder than the microwave background and would actually absorb energy.
- raattgift 10y ago
  Yes, and if we just accept arguendo that such black holes exist in our universe (and in reality they have not been precluded, as I note below), we have a density problem, although the argument is pretty Copernican (or alternatively rests on the cosmological counting system: forbidden, exactly one, mandatory). One problem with the argument that there is just one in the solar system is that unless it's unique, we would expect to see effects on star motions on a large enough number of nearby stars that one has to be inventive in attempting to explain why we haven't notice that yet. Worse, you would expect that at least one PBH would be near each supernova, and would interact with remnants, and that does not appear to be the case. Additionally, even if there was one in essentially every star system in every galaxy, they're still a tiny fraction of the dark matter sector, and we'd have to work even harder on an explanation for the core-cusp problem. That said, ~ the high end of sublunar mass PBHs (~ 10^23 kg) is about the least constrained mass region, so it's not surprising that people speculate about ~ M_earth PBHs. "[H]ow it came to be associated with our solar system" is fairly straightforward -- the field of PBHs existed before large structure formation, so you have the question a little backwards. The PBH was here first and its perturbations of the pre-sun GMC would have influenced the formation of our solar system. The question is whether those perturbations conflict with reasonable hypotheses for the formation and evolution of the solar system (and its predecessor). And again, you would expect PBHs to be involved in most similar star systems, and get to wonder about the gradient of such tiny black holes from the centres of galaxies to space outside galactic clusters. (Extragalactic space inside galactic clusters is maybe worse: there's invisible mass-energy among the galaxies mixed in with dust and gas, so why aren't stars forming there if the density of small PBHs is roughly similar to the outer edges of galaxies within the clusters? And if the density is very different, then why?) Finally, https://arxiv.org/abs/1607.06077v3 https://arxiv.org/abs/1607.06077v3 is very fresh and lists some further relevant constraints, but leans especially on https://arxiv.org/abs/1301.4984 https://arxiv.org/abs/1301.4984 .

bmm6o 10y ago

> Mercury's wobble was eventually explained by the theory of general relativity So, explaining the observations only took an entire new branch of physics? Only in hindsight is "maybe we don't understand how things move through space" the more obvious explanation than "maybe there's something there we haven't seen".