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B Black Holes & Dark Energy

  1. Jan 19, 2017 #1
    so, i love physics, and the more i look the more it seems our understanding of things are wrong. no planet #9, but now a mysterious planet-nine, dark energy, etc etc.

    so my question probably lies in theory, but getting close to applied physics.

    planet-nine, from what i have seen, the prediction model predicts a mass in orbit which is very very far away. cant this be a black hole or some other cluster of dark matter?

    as for black holes, they were very mysterious until the concept of dark matter/energy came to light. cant we explain a "black" hole in terms of a collection of dark matter/energy?

    and does anyone believe that we can some day have some tools to observe dark matter? or is it believed that we can only describe the theory via math? if you have a working theory that is 100% described by math yet we cannot make the observation, where does that put the problem?
  2. jcsd
  3. Jan 19, 2017 #2
    I am a physics freshman student.so I am not an expert but I just wanted to share my opinion.
    1-I dont think that it can be a black hole.Black holes are huge enough and the affects of a black holes are observable.(If there were a black hole we would be never been here at all,like solar system would never be created cause we need a huge massive star for a black hole)simply that cannot be a black hole.
    2-Also It cant be a dark matter cause dark matter affect galaxies in generally.Its affects are observable in large scales.I dont think it will affect anything at all.

    Hmm Black holes are result of GR.I dont know where you heard Black holes concept came from DE or DM but I dont think thats true.
  4. Jan 19, 2017 #3
    they are philosophical/theory questions, and not based on any other work or person.

    it has been said by the very guy who killed planet #9 and has theorized planet-nine that the prediction is so far away its almost impossible to find. with that said, why is the concept of a small black hole, one with the predicted mass, out of the question? black holes are already not ez to find, so a small one way way out there would be even harder. the prediction made was a chunk of observable mass which makes the item big, yet the distance makes it hard to find (a conundrum, like an infinitely big chunk of mass that is infinitely far away, likely cant find it, etc). a small (tiny) BH can explain the mass in the prediction, and at the same time be very very hard to find.

    as for DE making a BH, maybe GR is caused by the DE, on a different scale from what we normally know of observable mass creates GR. perhaps different types of energy/matter creates different types of GR?
  5. Jan 19, 2017 #4
    If the mass supposedly orbiting our solar system was a black hole, we would begin orbiting it and eventually get "sucked into" it. That itself basically rules out the black hole possibility. I'm not sure how this relates to dark matter and dark energy, though.
  6. Jan 19, 2017 #5
    why's that? regardless of what it is, just based on the predicted mass, we are currently not getting "sucked into it". so whether it be a object of mass XYZ, why would a BH of mass XYZ be any different? the BH would be technically extraordinarily small compared to what we have seen before, etc.
  7. Jan 19, 2017 #6
    Black holes are thought to be singularities in spacetime with infinite density, and they create incredibly strong pulls of gravity. There is no physical way that we wouldn't start orbiting a black hole.
  8. Jan 19, 2017 #7
    I agree with him.

    You need some logical arguments to say those things about GR.Can you refer me any referance about those ideas.
  9. Jan 19, 2017 #8
    strong pulls of GR? isnt that because a BH usually has and enormous amount of stuff in it? more stuff in it = more GR. whats to say we cant have a small BH that has not so much stuff in it? in other words, if i have a planet (object) that is 1x10^10000000 solar masses, and a BH that is 1x10^10000000 solar masses, isnt their GR effect the same?

    i have no references.
    and why cant a BH simply "shred" mass in such a way that what you get is, dark matter, hence why its a "black" hole. is it really a hole, or a sphere of dark matter?
  10. Jan 19, 2017 #9
    Ok using Schwarzschild radius and this info "The planet is estimated to have 10 times the mass , and two to four times the diameter of Earth" (from wikipedia)"

    Calculate and check that Is it fits
  11. Jan 19, 2017 #10
    The greater the mass, the greater the distortion on spacetime (aka greater gravitational pull). Even a small black hole has a relatively large mass that will still create huge gravitational effects.
  12. Jan 19, 2017 #11
    ok, i agree with you, but you missed my crazy idea. whether it be a BH or a chunk of observable matter, if Mass(BH)=Mass(object-matter), and roughly the same density, then wont they both appear to have same affects in space due to GR?
  13. Jan 19, 2017 #12
    Yes they would, if they have the same mass as you say. At the same time, that would rule out any chunk of matter at such a large mass because of the incredible effects of gravity (which would pull us to it instead of the sun pulling us).
  14. Jan 19, 2017 #13


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    Really? The more I learn, the more I find that things fit together. Things which were previously strange and unknown to me suddenly fit into place.

    It's not likely to be a black hole because there's no known way for a black hole with such a small mass to form. It can't be dark matter because our understanding of dark matter says that it doesn't clump together like regular matter does, so there's no way for it to form a compact object. Basically dark matter is thought to pass right through itself and regular matter, so it can't form compact objects like planets, stars, etc.

    Dark matter and energy have nothing to do with black holes. Neither concept affects our understand of black holes in any way.

    We can already observe dark matter by observing its gravitational effects on other objects. However what you're probably asking about is if we can ever observe dark matter through non-gravitational means, or on a very small scale like in a laboratory. Neither of these are likely to happen in the near future. If dark matter only interacts through gravitation then we will never be able to observe it except by looking at gravitational effects. And since gravity is the weakest of the four fundamental forces, we'd need a very compact dark matter object to observe it on a small scale, which can't happen since dark matter can't clump up in the first place.

    But who knows. Maybe some engineers/scientists somewhere will prove me wrong. :rolleyes:

    Not true. A black hole does not suck objects into it any more than the Sun sucks the planets into it. In fact, if we replaced the Sun with a black hole of equal mass, there would be almost no effect on the orbit of the planets. They'd still retain nearly their exact orbits. A black hole with the mass of a moderately sized planet would have a negligible effect on our solar system. We certainly wouldn't begin orbiting it and then be sucked in.

    It can't shed mass because there is no known way to get matter back out from beyond the event horizon. Once beyond the EH, all paths through spacetime take you to the singularity.

    That being said, quantum theory predicts that particles and radiation will be created just outside the event horizon. This is called Hawking radiation and leads to a mass loss from the black hole. I want to make it clear that these particles are created outside of the event horizon. They are not present in the black hole.
  15. Jan 19, 2017 #14


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    If the mass of the two objects is the same, then their gravitational effects are nearly identical if you are a large distance from each object (distance much greater than the radius). But there would be some small differences, especially if the objects are rotating.
  16. Jan 19, 2017 #15


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    Planet nine cannot be a black hole because it would expose itself as an xray source.
  17. Jan 19, 2017 #16
    I guess so. I will revise that to say sucked "towards" it, although I have read before that matter can eventually spiral down to the event horizon after a few million years. But are you certain that a black hole wouldn't change other objects orbits? An object with a mass of that magnitude should drastically alter the spacetime around it and cause other objects to orbit towards it.
  18. Jan 19, 2017 #17


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    Of course it would. Since most black holes have masses several time that of our Sun, such an object near our Solar System would have torn the outer planets out of their orbits long ago. Hence... :smile:
  19. Jan 19, 2017 #18
    Okay. Thanks for clarifying. Not sure if I misinterpreted what Drakkith said or not.
  20. Jan 19, 2017 #19


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    A mass of what magnitude? The mass of the Sun or the hypothetical planet? A 1 solar mass black hole behaves almost identically to a 1 solar mass star, and a 10 Earth mass black hole would behave almost identically to a 10 Earth mass planet, as long as you are far enough away from the event horizon for relativistic effects to be negligible (so greater than perhaps a few hundred to a few thousand radii).

    Also, the idea that it should "make other objects orbit towards it" indicates to me that you aren't that familiar with how gravity and orbits work. A very basic explanation is that you don't have one object orbiting the other. Instead, both objects orbit about their combined center of mass, called the barycenter. For example, the Sun and Jupiter both orbit about a common point that is located outside of the Sun. So if you went above the plane of the solar system and watched the position of the Sun relative to the background stars over the course of one of Jupiter's years, you would see the Sun slowly move around this barycenter.

    A black hole of several Earth masses cannot greatly effect the rest of the solar system simply because it isn't massive enough. Yes, if you get very close to the event horizon you will experience very strong gravitational effects, but only because all of the mass of the black hole is concentrated into a region about 10 mm across. Once you're thousands of kilometers away all of those relativistic gravitational effects have dropped off significantly (so you can get turned into human spaghetti when you're 1 meter from it perhaps, but at 10,000 km you'd barely notice anything).
  21. Jan 19, 2017 #20
    i wrote "shred", not "shed".

    my days of educational physics have come and gone, got though quantum physics, wave equations, with A+ grades, yada yada yada. so for the most part, i understand the solar system, to some extent, as an undergrad, from 20yrs ago, etc.

    my crazy questions are just that, wild theoretical questions, possibilities, etc.
  22. Jan 19, 2017 #21


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    Ah. I assumed it was a typo. My mistake. To answer your question, no, a black hole doesn't shred mass.
  23. Jan 19, 2017 #22
    i dont mean shred as in destroy it, i mean shred as it suck it in, destroy its binding, convert it to something else, perhaps dark matter. aka, matter that is "dark", like a "black" hole. perhaps an un-explainable process doing something we never did imagine, like thinking the sun was just a object of light, but then later come to find its a billion atomic bombs per sec process going on, being held in sensitive equilibrium by gravity.

    and i see where you posted that DM and DE cannot make up a BH. but perhaps that is the understanding today, and maybe in 200yrs the understanding will be different?
  24. Jan 19, 2017 #23
    The lightest (mass-wise) black hole that scientists have discovered, I believe, is about 3.8 solar masses, and it has a radius of about 12 kilometers. Now consider the facts that planet 9 is estimated at about 13,000-26,000 kilometers in radius, and that the radius of the event horizon in a black hole is directly related to the mass of the black hole. This mass would be MUCH greater than that of Earth or the Sun as you say. For example, a black hole the mass of Earth would only be about as big as a marble--- that is, the event horizon, not just the singularity.
    So, this body orbiting beyond Neptune has to be a lot more massive than you say. Using the Schwarzchild radius equation,
    and solving for mass M, the calculation would come out to be about 4400 solar masses (I only solved for the 13,000-km possibility). To sum up, if the "planet 9" was actually a black hole, it would have a mass of approximately 4400 solar masses. What kind of effects would that have on our solar system and its orbits?
  25. Jan 19, 2017 #24


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    In the end, the matter and radiation taken up by a black hole is probably converted to hawking radiation.

    Extraordinarily unlikely for dark energy which isn't even remotely related to black hole physics. A mole is more related to its mountain than dark energy is related to black holes.

    Dark matter is slightly more plausible, but given that current understanding suggests that dark matter cannot clump together in the first place, there is just no known way for a large amount of dark matter to make it into a black hole. Certainly a small amount might. But we're talking tiny fractions of a single percent at best.

    In any case, remember that we discuss mainstream science here at PF, not what-if's about the future or other speculation. Please try to stay in that realm or I will have to lock this thread.

    Not true. The size of the planet is determined by first finding the mass, not the other way around.

    Devastating. Absolutely devastating.
  26. Jan 19, 2017 #25
    Sorry. When I said body, I was using the assumption it was a black hole, not a planet.
    So it does rule out a black hole as a potential for this "planet 9"?
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