# Is it possible to move a black hole?

My fascination with black holes runs very deep. I was wondering if anyone could shed some light on two questions I have:
1. Do black holes orbit around another object, or are they "free-roaming"? If they do, what determines which object they rotate around? The place where they form, or some other external factor?
2. Is it possible to change the vector of a black hole? To physically move it in space? If yes, what forces would be involved in such an activity, and is there an equation that resolves the force necessary to move a black hole with a set mass and dimensions?
Apologies if these questions have been answered elsewhere, but I couldn't find them. Also if the post is in the wrong forum feel free to move it wherever is more fitting.

Many thanks!

## Answers and Replies

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PeroK
Homework Helper
Gold Member
Black holes behave gravitationally the same as the collapsed star that formed them. Unless you get within the radius of the previous star. In that sense there is nothing special about their motion under the gravity of other massive objects.

etotheipi, russ_watters, Alex Ford and 1 other person
Black holes behave gravitationally the same as the collapsed star that formed them. Unless you get within the radius of the previous star. In that sense there is nothing special about their motion under the gravity of other massive objects.
My main question doesn't concern the, "...moving a Black Hole off its Vector." Rather it concerns the direction of the swirl in which energy/matter are, "...sucked in towards the event horizon and continue in that direction after having been, "pulled in," by the gravitational force (not concerned at this point with strong or weak as to me, it must be pretty strong to destroy a star, for example). Are there also Black Holes that have a swirl pattern that are opposite in direction to the usual direction (clockwise or counterclockwise?) of the, "pull of the material in a swirl.

I think an examination with a miniature black hole experiment, here on earth, could answer the question of varying densities (or not) as the journey deeper into the Black Hole is accomplished during the Spacetime continuum. There really is one constant in the universe and that is the constant of, "motion." Alex Ford

weirdoguy
Staff Emeritus
2019 Award
I understand little of what you wrote, but clockwise rotation looks counterclockwise from the other side.

etotheipi
Ibix
Are there also Black Holes that have a swirl pattern that are opposite in direction to the usual direction (clockwise or counterclockwise?) of the, "pull of the material in a swirl.
This appears to be more or less a duplicate of your question here and suffers from the same basic problem that it makes no sense. Whether matter falling into a black hole (or anything else) is moving clockwise or counter-clockwise is a matter of perspective.
I think an examination with a miniature black hole experiment, here on earth, could answer the question of varying densities (or not) as the journey deeper into the Black Hole is accomplished during the Spacetime continuum. There really is one constant in the universe and that is the constant of, "motion."
This makes even less sense. You should probably check the forum rules, specifically the parts about personal theories (you need to understand current theory before you can speculate usefully on extending it) and thread hijacking (you should start your own thread rather than posting tangentially related stuff on someone else's thread) before continuing to post.

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phinds
Yeah, not sure what you're on Alex, seems like you didn't even try to answer my question.

Black holes behave gravitationally the same as the collapsed star that formed them. Unless you get within the radius of the previous star. In that sense there is nothing special about their motion under the gravity of other massive objects.
Sorry if I seem silly, but I really don't understand what you mean by that. To further clarify my point, I'll pose it as follows - is there a way that I can push a blackhole towards some object in space? For example, I might want to take a black hole and shove it in the direction of a massive star with the intention of destroying that star. Can I do that, and if yes - what kind of force would be sufficiently powerful to be able to move an object as dense as a BH without actually falling beyond the event horizon? Would an object with sufficient gravitational pull positioned behind the BH in the intended general direction do the job? Or will there be some sort of gravitational interference and interaction that would complicate things beyond feasibility?

PeroK
Homework Helper
Gold Member
Sorry if I seem silly, but I really don't understand what you mean by that. To further clarify my point, I'll pose it as follows - is there a way that I can push a blackhole towards some object in space? For example, I might want to take a black hole and shove it in the direction of a massive star with the intention of destroying that star. Can I do that, and if yes - what kind of force would be sufficiently powerful to be able to move an object as dense as a BH?
A star and a black hole may collide like any two objects. Your question is no different from asking whether the Earth would collide with the Sun if its orbit could be changed. Black holes from a distance are simply gravitational masses.

Epsilon Eridani
A star and a black hole may collide like any two objects. Your question is no different from asking whether the Earth would collide with the Sun if its orbit could be changed. Black holes from a distance are simply gravitational masses.
Ok, so I can physically move a BH through space if I had a source of strong enough gravity that I can get close enough to the BH to affect its vector. Kind of like pulling a piece of metal with a magnet. Thanks for answering!

Ibix
Sorry if I seem silly, but I really don't understand what you mean by that. To further clarify my point, I'll pose it as follows - is there a way that I can push a blackhole towards some object in space?
You can pull it around with gravity. If it's charged, you can pull it around with electromagnetic forces.
Can I do that
In principle. Generating enough energy to affect the trajectory of an object of stellar mass is left as an exercise for the reader.

As @PeroK says, as long as you don't get too close, you can move a black hole around just like a star, using the gravitational effect of other stars, black holes, planets, etc. The only problem is the sheer scale of shoving that much mass around in any meaningful way. That puts it out of reach of even Star Trek "science".

Epsilon Eridani
You can pull it around with gravity. If it's charged, you can pull it around with electromagnetic forces.

In principle. Generating enough energy to affect the trajectory of an object of stellar mass is left as an exercise for the reader.

As @PeroK says, as long as you don't get too close, you can move a black hole around just like a star, using the gravitational effect of other stars, black holes, planets, etc. The only problem is the sheer scale of shoving that much mass around in any meaningful way. That puts it out of reach of even Star Trek "science".
Thanks a lot for clarifying! The sheer scale of such an operation can fit comfortably in the grasp of the boundless possibilities within the sci-fi genre. If Star Trek didn't do it, I'm sure some Kardashev Type III civilization from a faraway galaxy will be able to figure it out.

PeroK
Ibix
Back of the envelope, if you capture the entire power output of the Sun and turn it with 100% efficiency into motive power it would take eighty years to affect its velocity by 1km/s. Stellar velocities tend to be around ten times that, so upwards of ten millenia to bring it to rest with respect to nearby stars. And then a comparable time frame to reach the nearest star at that kind of velocity - so it's a multi-millenium project even with that kind of energy to throw around.

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etotheipi and Epsilon Eridani
berkeman
Mentor
Thanks a lot for clarifying! The sheer scale of such an operation can fit comfortably in the grasp of the boundless possibilities within the sci-fi genre. If Star Trek didn't do it, I'm sure some Kardashev Type III civilization from a faraway galaxy will be able to figure it out.
Did you mean to post this in the Sci-Fi writing forum? I can move it there for you if that was your intention...

Epsilon Eridani
Back of the envelope, if you capture the entire power output of the Sun and turn it with 100% efficiency into motive power it would take eighty years to affect its velocity by 1km/s. Stellar velocities tend to be around ten times that, so upwards of ten millenia to bring it to rest with respect to nearby stars. And then a comparable time frame to reach the nearest star at that kind of velocity - so it's a multi-millenium project even with that kind of energy to throw around.
I had no idea it took so much force to move a stellar object. Wow... Maybe one could shorten that time if there was a way to, say, locally and temporarily suppress inertia? That's of course in the realm of complete sci-fi, but still. Reynolds used inertia-suppressing technology in his Revelation Space saga.

Did you mean to post this in the Sci-Fi writing forum? I can move it there for you if that was your intention...
Apologies, I didn't know there was such a forum. Please move it there, you're spot on regarding my intention.

Thanks!

berkeman
Ibix
Did you mean to post this in the Sci-Fi writing forum? I can move it there for you if that was your intention...
...and if so, I can think of at least two scifi writers who've used micro-black holes as weapons. That's somewhat less unrealistic.

berkeman and Epsilon Eridani
...and if so, I can think of at least two scifi writers who've used micro-black holes as weapons. That's somewhat less unrealistic.
The authors that have used BHs as weapons are probably way less than those that have used antimatter projectiles And when I say "used" I mean doing so convincingly.

In Neal Asher's recent Rise of the Jain trilogy moving a black hole has some dire consequences, but it's not even speculative sci-fi, it's science fantasy, which I guess you need to even hypothetically posit moving a large BH.

stefan r
In Neal Asher's recent Rise of the Jain trilogy moving a black hole has some dire consequences, but it's not even speculative sci-fi, it's science fantasy, which I guess you need to even hypothetically posit moving a large BH.
It would be hard to not move a black hole. Any spaceship flying near one would follow a hyperbolic orbit. For every action there is an equal and opposite reaction. You would need two space ships to follow opposite prograde and retrograde orbits. Maybe there is a narrow path where the ship does a full 360 around the black hole and continues on the same path it started on. Space probes like Voyager or New Horizon moved Jupiter.

..., so upwards of ten millenia to ...
Lunar mass black holes could be moved using a millionth of the momentum compared to stellar mass black holes.
We don't have the tools to see a Lunar mass black hole in our own Kuiper belt. I'm not saying there is any good reason to believe we have one. Just if we did have one there it would not have been noticed yet.

There has been a suggestion that a 5 Earth mass black hole could explain the orbits of other Kuiper belt objects.

..., to bring it to rest with respect to nearby stars. And then a comparable time frame to reach the nearest star at that kind of velocity -...
Why are we brining it to rest? Let it keep going as it was. Adjust the aim very slightly so that it passes closer to a star that it was going to pass close too anyway.

... even with that kind of energy to throw around.
We can throw around a lot of energy if we have mass and we have a black hole. The energy released by fuel dropping into the black hole is much higher than what you can get from nuclear fusion. The black hole could be in a binary or have surviving planets. There could also be stellar mass fleets of ships that could use the black hole for the Oberth effect.

The person who started the thread wants to take apart a large star. If there happens to be a black hole flying near the target star then it might be easier to redirect the black hole. Other methods of taking apart starts require lots of energy and time.

Why most certainly! Here's my little trick that I played to draw my conclusion:

Galaxies are formed around massive blackholes.

Galaxies move around and sometimes they collide. Our Milkyway galaxy will collapse with... that, that galaxy... well that! (pointing finger up frantically) galaxy in about a couple... million? of years so of course blackholes move and yes they just have to be able to be moved, like, by another massive galaxy.

DaveC426913
Gold Member
Galaxies are formed around massive blackholes.
I'll have to check my facts but I think the prevailing understanding is that galaxies formed first and black holes formed at their centre.,

Galaxies move around and sometimes they collide. Our Milkyway galaxy will collapse with... that, that galaxy.
They'll pass through each other and emerge highly distorted, but there will be relatively little in the way of collisions.

stefan r
stefan r
They'll pass through each other and emerge highly distorted, but there will be relatively little in the way of collisions.
But the number of near misses will be truly abundant.

The whole Andromeda galaxy is only 3 degrees by 1 degree or so wide. That is like the triple 20 spot on a dart board from a reasonable distance. Since things in the Milky Way are orbiting the Milky Way you just have to adjust timing.

Meters/second is not too far off from parsecs/billion years. That alone should be enough for some star to line up. While crashing through a galaxy you have a few dozen kiloparsec pathway. You should need less than a few mm/s delta-v to line up some sort of direct impact.

All this planning and effort will go down the drain if intelligent life emerges somewhere in Andromeda. You have to second guess where the Andromedans will move their stars. Worse than playing chess with billions of pieces.

PeroK and berkeman
I'll have to check my facts but I think the prevailing understanding is that galaxies formed first and black holes formed at their centre.,
Hah, I'll be perfectly honest I had always assumed (which is a very bad practice) massive blackholes form first due to super-super nova collapsing, then other still massive, but nevertheless relatively smaller stars, formed by dust cloud no less, gradually form galaxies, in heaven-knows how many years.

They'll pass through each other and emerge highly distorted, but there will be relatively little in the way of collisions.

Yep, it still gets me sometimes. They are unimaginably gigantic with a lot of "empty" space in between.