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Black Hole Jet Emissions

  1. Jul 13, 2010 #1
    I just read an article about recently observed jets emitted from a black hole, apparently due to the extreme acceleration of something falling into it. Now I'm wondering what would happen if the object accelerating into the black hole was another black hole. Yes, black holes are expected to devour any energy that crosses their event horizon, but as a whole would one not behave similarly to a non-black hole, possibly generating similar jet emissions? If so, would this be a mechanism for black hole gravitation and inertia to be converted into free radiation emissions? Or could such a black hole simultaneously generate radiation from acceleration and absorb it completely?
  2. jcsd
  3. Jul 14, 2010 #2
    Interesting idea brainstorm, but there's one piece missing: its not JUST the act of infalling that creates the jets.

    Whats happening is that, lots and lots of dust and gas and maybe planets and starts (etc etc) are falling towards the black hole. As they fall, they move faster and faster; and eventually start colliding with each-other. The infalling material gets really hot as it falls towards the black-hole, and because its so hot it radiates light (x-rays mostly, but lots of good stuff) and particles. Generally, all of the infalling material is coming from an accretion disk around the black-hole, which only leaves two openings on each end for the radiated energy (light and particles) to be emitted from (magnetic fields can also help 'beam' these emissions) which appear as jets.

    A second black-hole, falling into the first, wouldn't be able to heat-up and radiate in this way, so it would remain (for the most part at least) invisible from light.
  4. Jul 14, 2010 #3
    As I understand it, the energy of particles with mass must increase to infinity to reach the speed of light. As a result, I assume that acceleration of particles approaching the speed of light generates energy approaching infinity. Since infinite energy is impossible, I assume that anything approaching the limit has some sort of breaking point where it dissipates energy as something other than continuing acceleration. In the case of a black hole, I wonder what happens when the total energy it has achieved through acceleration approaching C exceeds the amount of mass/gravitation it exerts. If it becomes angular momentum, couldn't the black hole outspin its own gravity?
  5. Jul 15, 2010 #4
    This is true, but particles aren't being accelerated to the speed of light as they enter a black hole, just to some high (possibly relativistic) velocity.

    Some of the energy from that acceleration is dissipated in heat, and in the jet; the rest is incorporated into the black-hole, which then grows (the event horizon expands)--there is no limit to how much energy a BH acquires (to our knowledge).

    I'm not especially familiar with rotating ("Kerr") black-holes, but as their angular momentum grows, the event horizon in the plane of rotation also expands (so its no longer spherical, but oblate). There isn't any way that the spinning could tear it apart; no amount of force is enough to break apart a black-hole.
  6. Jul 15, 2010 #5
    I don't know what you think causes EM radiation to be emitted from matter, but my impression is that it due to particles, usually electrons, accelerating to near-C velocities. To me, it makes sense that if an electron or other particle cannot express an increase in force as kinetic energy of motion, because an increase in velocity requires more energy than is available, the particle has to dissipate the energy in another form. Photons are the logical candidate since they consist of fields inherent in electrons and can accelerate to C without infinite energy.

    Radiation produces KE-heat (molecular motion) when it strikes matter, correct? So, if radiation entering a BH does not somehow get converted into matter, then it must increase the KE-heat inside the event horizon. The question is what happens to that KE-heat in a gravity situation that prevents expansion. Presumably the contents of a BH are already some sort of plasma, right? So how else could additional KE be expressed except as turbulence or spin? If the event horizon keeps reflecting any radiation released from the plasma back into it generating turbulence and spin, the angular momentum of the plasma-ball would keep increasing, no? So what about a black hole's gravity prevents its angular momentum from exceeding its gravitation? Granted, nothing can escape its gravity without exceeding C, which is not possible - but who says an internal fissure can't emerge from radial momentum such that the BH splits into multiple smaller BH's?

    [/quote]I'm not especially familiar with rotating ("Kerr") black-holes, but as their angular momentum grows, the event horizon in the plane of rotation also expands (so its no longer spherical, but oblate). There isn't any way that the spinning could tear it apart; no amount of force is enough to break apart a black-hole.[/QUOTE]

    But if KE exceeds gravitational force, it has to be expressed somehow. Either there has to be infinite amounts of phase-changes possible that can occur within the BH to express growing energy, or fissures can emerge. I would expect this process to take place similarly to the way a ball of water in zero-gravity breaks apart, i.e. with the surface tension pinching together in each fragment separately to contain them into new units. In the case of a BH, gravity is analogous to surface-tension of water insofar as it is a force of compression and spherical-tendency.
  7. Jul 15, 2010 #6
    Okay, LOTS of issues here....
    There are many reasons for EM radiation, first and foremost black-body radiation from anything at non-zero temperature--and thats the primary mechanism of emission in BH jets. Also, any acceleration of charged particles emits radiation e.g. http://en.wikipedia.org/wiki/Larmor_formula" [Broken]

    Force always leads to acceleration, if the force is small, it will be a small acceleration, if the mass is big, the acceleration will also be small. There is no limit to how small of an increment of acceleration can be made, and an infinite amount of energy can therefore be absorbed as you accelerate something towards the speed of light--there is no need to dissipate energy. Also, being a little nit-picky, photons are be definition not fields, and most certainly do NOT accelerate to c, they're always going at c.

    The temperature (which is average kinetic energy, not "heat") is undefined INSIDE the event horizon. The event horizon itself has a low, finite temperature--but thats unrelated. The condition of the contents of a black hole is also undefined, but definitely not simply a plasma. The "size" of the contents of a black-hole are millions of times smaller than a single atom, if they have any "size" at all.

    The black-hole as a whole will have some kinetic energy, the whole thing can move. Otherwise the KE gets converted to mass-energy, just adding to the mass of the BH itself.

    For a BH to split into smaller ones, the smaller ones would have to escape eachothers event horizons, which is not possible. For the same reason the BH forms in the first place, there is no source of energy which can resist the gravitational pull/collapse.

    There is no need to "express" energy, I don't know what you mean by that. Energy is never 'competing' against gravity, only other forces are--and in the case of a BH--they always lose. It doesn't matter how much mass/energy is in the black-hole, that just makes the BH bigger and stronger.
    Last edited by a moderator: May 4, 2017
  8. Jul 15, 2010 #7
    Thanks for this link. This is new information to me. I thought particles could express all their energy as motion up to a certain velocity.

    This is how I see this, and it may be misguided: if a particle is traveling at close to C, let's say 99.5%C (I'm not a physicist so excuse me if I'm overlooking something in choosing this as an arbitrary speed for discussion's sake). For the particle to accelerate from 99.5% to 99.6%C it has to jump forward in its inertial frame a certain distance, which would be relatively far compared with the same acceleration taking place at a fraction of C, right? So such a jump seems analogous to the jump that occurs between molecules in chemical reactions or static-electricity sparks, or in LED emissions. In other words, an abrupt particle-jump emits radiation, imo, because of a ratio between its energy and the distance across which it is accelerated, hence dissipation of surplus energy - or maybe better stated as the particle's energy getting ahead of itself.

    LOL! You say they're undefined and then proceed to define what they're not. The only thing I meant by "plasma" is that nuclear particles are compressed beyond the isolating-force of their electron shells. All I meant is that very heavy particles are moving at extremely close proximity, which involves a lot of particulate momentum counteracting a lot of particle attraction. In any case, my point was that I think whatever the state of material inside a BH, it must have a limit as to how much energy it can absorb as changes of phase/state. After that, I would expect energy to be expressed as system-level motion (i.e. turbulence or spin).

    If infinite phase/state changes are possible, then BH's could infinitely absorb energy. Likewise, if energy can be sustainably transformed into matter or otherwise increase the gravitation, then the event horizon would simply expand indefinitely. Still, I don't see why a BH couldn't spin fast enough to cause it to split into multiple smaller BHs. System-level motion is different than particle-energy or radiation.

    How does KE get converted into mass-energy exactly?

    Not if gravity is being expressed in the re-sphering of the two halves. Think about a ball of water in zero-gravity. No drop of water can escape the surface tension of the water, but when elongated enough, the ball will split as the two sides re-sphere according to the surface tension being distributed to the ends instead of the center.

    All gravitational systems express energy as motion. This could be rotation or orbiting satellites. Planets, moons, and other satellites maintain radial distance from their fulcrum according to their velocity which "competes" with gravity to establish the object's distance from the center of gravity. If velocity wins, the object's distance from the center increases. If gravity wins, velocity isn't sufficient to maintain orbit altitude and the object begins to fall deeper into the gravity well.

    A planet whose rotation increases sufficiently would overcome its own gravity and fragment into divergent pieces. As long as the planet's gravity is sufficient to overcome the momentum of its constituent parts/particles, the planet remains intact. Heavier particles require more energy to overcome gravity so they can withstand greater velocities and lower gravitation before floating away.

    Take a practical example: First make a chart correlating Earth's rotational speed with its rate of gravity at sea level. Then find the rotational speed at which water boils at 0C. Then figure out the point where gravity is no longer sufficient to prevent the water molecules from blowing away into solar orbit. Eventually, I assume you'd reach a point where the spin would overcome the force holding the core together and the planet would split into multiple moons in mutual orbit.
    Last edited by a moderator: May 4, 2017
  9. Jul 15, 2010 #8
    No, not at all. For the particle to accelerate from 99.5% to 99.6% of c, it would do so continuously, smoothly, not in steps. And it has nothing to do with a jump in distance.

    They're undefined, but I can still say they're not (for example) a banana, or a chevy. Again, he stuff in a black hole is MILLIONS of time SMALLER THAN AN ATOM. There are no more "electrons," "protons," "atoms," etc... not even quarks. Possibly A STRING, but thats neither here nor there. Its not a structured assembly. It has no bulk motion, flows, swirls, or slow-dances. A BH does not have phase changes. It can still infinitely absorb energy.

    You're completely not getting it. A drop of water (apparently and clearly) CAN escape its surface tension. I.e. you just poke it, or you tip the glass over, or you shake it, or heat it, etc etc etc. Matter CAN NOT escape an event horizon! Space-time is bent to such an extent that a path leading out, DOES NOT EXIST.
  10. Jul 15, 2010 #9
    Ok, maybe I can put it this way then: radiation is a pure expression of energy. Material particles accelerate to express energy as higher velocity. If a particle received enough energy to accelerate beyond C, some of that energy would have to be dissipated as radiation because it couldn't be expressed as motion. So, theoretically, that is the same thing that happens at speeds close to C, only the amount of energy liberated has to do with a relative amount of "friction" based on the exact speed and amount of energy added to the particle. I think it is the same process as black-body radiation intensification, which I think also has to do with particle-systems (i.e. atoms) receiving amounts of energy sufficient to push them to near-C velocities. Do you think there's no relationship between KE and EM radiation emissions?

    Ok, what about square dances then?:) Seriously, though: What do you base your notion that matter keeps breaking down into increasingly small particles of matter? You say "string," but what is that? A vibrating segment of pure energy that doesn't move at C? By "phase change," I generally mean re-configurations of matter-energy that would allow it to be compressed infinitely. If there is a limit to matter-energy compression, then energy within a BH would have to be expressed in some other way for it to be conserved, no?

    You don't see the difference between matter or energy escaping the event horizon and the BH as a whole pinching into two halves? You mentioned the possibility of shape-change in a rotating black-hole due to rotation momentum, right? If rotation can deform the BH, surely it could be stretched to the point where the gravitation in each half overcomes the gravitation of the center toward the halves. At that point it would split, no?
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