would it be possible to sling shot an oject to near light speed using a black hole gravity to slingshot it?

Question

just like nasa uses the gravity field of planets to sling shot space probes to other planets in our solar system, than theoretically wouldnt be possible to accelerate a space ship to nearly the speed of light using this same principle and by using the gravity field of a rotating black hole, assuming that the space ship didnt cross the event horison, and assuming that the same ship was built in a manner that could withstand the gravitational forces, inertial forces, and the centrifugal force created by the acceleration.

Answer 1

You sure could slingshot something but it won't be the same shape it started off. If you want to get to near light speed you will have to get really close. The gravity field has such a steep gradient it will rip apart the atoms in the strongest materials.

Answer 2

NASA uses the gravity both of the sun and a planet (neither alone) to slingshot objects through the solar system. All the planetary object can do in the absence of it's orbital velocity is turn the spacecraft to a different direction. If this is done properly a spacecraft gains or loses velocity by being dragged along the orbit of a planet (along with the change in direction) either in the same direction as the planet orbits (gain in velocity) or in the opposite direction (velocity loss). The orbit of the planet is dictated by the strength of the gravity of the sun and it's distance.

If the spacecraft passes the planet across it's orbit rather than along the orbit (over the poles, for example, if the poles point normal to the orbital plane) there may be no permanent change in speed but only a change in direction. (There is a solar probe out there right now that went all the way to Jupiter, crossed that planet's orbit across it's polar regions, and reversed direction, back toward the sun, but with little change in speed).

So, if an object entered the gravity field of a black hole and managed to come out again it's speed would be the same as it was before the close encounter, if the before and after distances to the black hole were the same. It could be accelerated to near light velocity at one or another point, but it would then slow just as much as it sped up.

Notice I changed rather abruptly here and there from using the term velocity to the term speed. That's because speed is change in position divided by time, whereas velocity dictates acceleration (which can mean same speed, different direction).

Answer 3

Yes. And if it were a really big black hole, like the ones in the centers of galaxies, the forces on your object wouldn't even be that high. The bigger the black hole, the smaller the tidal forces and the acceleration forces. For a truly gigantic black hole, the forces are tiny.

P.S. The solution to epidavros' objection is that to make the slingshot work, you have to eject something from your spaceship (i.e. do a rocket burn) when you are near the event horizon. The kinetic energy you gain far from the black hole is approximately equal to the rest mass energy of the stuff you eject.

Answer 4

Simplistically a black hole is an object with an escape velocity equalt to the speed of light. The escape velocity is the velocity you would need at the event horizon to reach infinite distance with an ultimate zero speed. So, by definition, it must be possible to accelerate an object close to the speed of light by having it fall towards a black hole from infinity.

However, as a slingshot its pretty much a non starter. This is because as the object receded from the black hole its gravity would act to slow it down again, ultimately to zero speed of course.

Answer 5

This depends on your definition of 'near light speed' really
how near? Remember that c isn't just the speed of light, it a fundamental part of how time and space are joined.

consider E=(delta)MC(squared)
if you are applying energy to a mass to make it accelerate you have to accept that the mass of the object would increase as you approached the speed of light. given that the the mass increases the amount of energy required also increases, until, at the speed of light the mass is infinite, and thus so is the energy required, thus making it impossible.
it is very unlikely that your spaceship could gain enough energy to even to make a close approach to the speed of light without falling foul of the black holes gravitational field.

special relativity is a pain in this situation, unfortunately you cant even get round it by setting up your deck chair and settling down in a different inertial frame, seeing as the speed of light is the same in all frames.

brilliant question though :)

charlie

Answer 6

nice idea, but no, since the gravity from a black hole pulls stuff in and it would be impossible to escape. The speed of light (186,000 m/sc) would be impossible to reach, I think that that guy Einstine proved in his GTR thing. E=MC x C, don't know how to put squared on this.

Answer 7

Be careful you don't accidently bump into a planet at light speed, and remember not to drink and drive as you go, else you get the risk of the interstellar police on your tail - and thats not a pretty sight!

Answer 8

No acceleration is lost as it escapes orbit of the black hole. they dont really sling shoot anything like that. they use that to make a coarse corection without using power.

Answer 9

near light speed, possibly, but it would lose a good amount of that speed pulling away.

Answer 10

you could give it a shot, but there is the risk of impregnating the hole creating interstellar overpopulation of black holes.