I identify four possible kinds of thrust below (there may be more or less). I don't know how to do the math to test them though.

  1. Direct transfer of kinetic energy as thrust. The energy of objects falling into the black holes themselves would transfer some kind of directional force, right?

  2. Ion thrust. Radiation/gases emitted by the black holes would act as a kind of thrust, right? I know that current models indicate an outflowing of energy from a black hole, a sort of constant flow. Is this outflow constant over the whole surface of the black hole, or is it more concentrated in some areas vs. others? If so, it might act as a form of constant propulsion, causing the black hole to accelerate over time.

  3. Gyroscopic thrust. I'm a little less clear here, but my understanding is that most black holes are constantly spinning. Could those be acting like gyroscopes and the gravitational energy of the matter spinning around those black holes acts as torque, causing the gyroscope to accelerate in a single direction over time?

  4. Heat differential. Are black holes a constant temperature across their entire surface? Or is there a heat differential in various areas, and could that heat differential (if real) act as thrust?

Taking the logic train further: (Feel free to poke holes, I know I make a lot of assumptions, probably based on fallacies.)

If any of these forces exist, the propulsion they exert on the black holes would be immense when factored over time (even taking into account the extreme mass of the black holes themselves). In fact, if these forces exist, it would stand to reason that the more massive a black hole is, the faster it would be accelerating in space.

Then, if black holes are accelerating, in what direction? I'm guessing they would generally accelerate away from the largest concentrations of mass, the impact of the mass itself propelling them in the opposite direction. I am less clear on the directional thrust of the radiation emitted or of any gyroscopic thrust.

But, if the supermassive black holes accelerate away from the largest concentrations of mass, then, over time, they are moving away from the center of the universe at an ever-increasing speed, right? This is assuming that mass in the universe is most dense at the core and least dense at the edges.

And, as these black holes move through space, they drag their respective galaxies along with them. Acting as galactic engines, propelling the expansion of the universe over time.

Lots of logical leaps, I know. But it was a fun ride.


closed as off-topic by Aaron Stevens, user191954, G. Smith, John Rennie, GiorgioP Mar 26 at 6:37

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Black holes don't have a physical surface. They do have an event horizon, but that's just a mathematical surface, similar to how Earth's equator is a mathematical line, not a physical structure on the globe.

Black holes (possibly) emit a tiny amount of energy (Hawking radiation) just outside the event horizon, but that has a temperature around a billionth of a degree above absolute zero for stellar mass BHs, and even colder on the big BHs.

Active black holes (that is, ones absorbing matter) have an accretion disk of matter that hasn't fallen in yet. (Black holes are pretty tiny relative to their gravity, so when there's a lot of matter trying to fall into the hole you get a traffic jam). Matter in the accretion disk is orbiting at a very high speed, so it has a lot of kinetic energy, and when matter crashes into the accretion disk the collision is very violent, giving off all sorts of radiation, including x-rays, and "shrapnel" gets ejected in polar jets. Those jets could give the BH some thrust, except that the jets are fairly well balanced, so the net force on the BH is pretty small.

The universe doesn't have a centre, or edges. Please see Did the Big Bang happen at a point?.

Stellar black holes are formed in supernova explosions, which tend to be rather asymmetrical, so the BH gets a kick when it's created, so it can have a substantial velocity relative to the stars in its galactic neighbourhood. But they don't have any active thrust mechanism after that initial kick.

We don't know exactly how the huge black holes in the centres of galaxies were formed. And although they do dominate the gravity in their immediate vicinity they do not dominate the whole galaxy: their mass is only a tiny percentage of the total mass of the galaxy. So even if they did have some kind of thrust mechanism happening it'd only affect the nearby stars, not the whole galaxy, so the BH would take off leaving most of the galaxy behind.

Black holes don't run away from matter, that would require some kind of antigravity.


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