What's the easiest way to move a star?

[TheDonk]

OK, I know it's difficult to move a star. But I'm trying to write some science fiction here and I want to make sure I'm consistent with astronomy and cosmology.

Now assume that over the next billion years we completely colonize the galaxy and we're all cooperative and stuff. What would be the easiest way to eject a star from the galaxy?

You can attach a rocket to an asteroid to move the asteroid.
You can even attach a bunch of rockets to a planet to move the planet if you're smart about when the rocket are turned on and off. (Remember, time is not a big issue. Say within 1 billion years.)
But you can't attach rockets to a star. What else could you do? Best idea I can think of is by moving heavy solid objects like planets into (well timed) close orbits that pull the star a little bit in the direction you want. Repeat a trillion times and you're done.

Would ginormous anti-matter explosions near the surface do any better?

There must be a way!

 

[ebits21]

The star would have to reach a certain escape velocity to permanently leave the galaxy. The only way to do it (I think) is to have the star slingshot around a supermassive black hole (like in the middle of the galaxy). Which I believe has actually been observed.

I don't think there's any other way.

 

[ebits21]

Here's an article from NASA on stars being ejected by a supermassive black hole. (http://www.nasa.gov/mission_pages/hubble/science/expelled-star.html" )

But really... you're never going to be able to tow our star to the galactic centre. And I don't think any other method would produce enough force.

 

[Hurkyl]

The first thing to note is that you generally don't want to propel any object directly along the path you want it to go -- you want to nudge it so that it will slingshot around other objects. Maybe there are larger stars "nearby" you could use, or maybe you could make use of a nearby cluster.

It's easier with planets, since there tend to be very massive objects nearby to slingshot around. (by the way, did you forget about gaseous planets? )



You can always shoot objects into the star, to transfer momentum directly. It would probably only be half as effective as using slingshots to transfer momentum to the star, but probably easier to aim. You can transfer momentum with light too; depending on the hypothetical technology it might be easier to aim a zillion lasers at the star rather than relying on massive objects to transfer momentum.

 

[Chronos]

As long as we are talking science fiction, a wormhole is a theoretical possibility. All you need is an industrial strength wormhole generator and a gazillion gigawatts. You can use your imagnination to invoke any of a number of plausible disasters that might arise.

 

[jimgraber]

A few ultrahigh velocity stars, i.e stars leaving our galaxy are actually known.
In real life the only two explanations actually considered are supernovae and near collisions involving three or more bodies. The three bodies can all be stars, but one or more could also be a black hole.

Jim Graber

 

[phyzguy]

We see a large number of "jets" at different scales. As matter spirals into a rotating black hole, it forms an accretion disk around the star's equator, and a large amount of the accreting matter gets ejected out the poles, forming oppositely directed jets. We see these things around black holes ranging in size from a few solar masses (stellar mass black holes) to billions of solar masses (super-massive black holes). If the oppositely directed jets were not perfectly symmetric, these things could be used as rockets. I was thinking that a neat idea for a science fiction story was an advanced civilization that found (or engineered) a stellar mass black hole with asymmetric jets and then went into a distant orbit around it and used the thing as a rocket to travel around. Just an idea.

 

[wolram]

What's the easiest way to move a star?

Tell him/her he/she has won an Oscar.

 

[Nicodemus]

Well, if we go full scifi maybe you ignite a 'nearby' hydrogen cloud and form a hyper-giant. That shockwave should be a good first move, and if you're taking the Sun there are things other than galactic nuclei that could get it moving.

Even in a sci-fi context however, the ability to move a star seems like a wasted investment.

 

[qraal]

OK, I know it's difficult to move a star. But I'm trying to write some science fiction here and I want to make sure I'm consistent with astronomy and cosmology.

Now assume that over the next billion years we completely colonize the galaxy and we're all cooperative and stuff. What would be the easiest way to eject a star from the galaxy?

There must be a way!

Fortunately there are several.

(1) Use big magnetic fields to channel the Solar Wind out one pole, thus turning the Sun into a rocket. The Solar Wind might be pushed to higher mass-loss rates and higher speeds, which Galactic escape will need. Just how fast? That's a bit tricky because of the Galaxy's Halo of mass - either Dark Matter or MONDian gravity - which means the Galaxy's effective mass increases as you move away from it. If we assume a maximum mass of ~1.2 trillion solar masses at a radius of ~150 kly, then the escape velocity is ~474 km/s. Our Solar Wind rocket would need a fast Solar Wind (say ~950 km/s) to eject about ~40% of the Sun's mass to push it to that speed.

(2) Surround the Sun with a perfect reflector to one side - thus creating a giant Photon rocket. Over the next ~5 billion years the Sun will produce enough light-energy to propel it to a speed of ~152 km/s. Not quite enough. So we need to up the luminosity. If we coaxed it to fuse all its hydrogen, instead of just ~10%, then we'd be pushing towards 1,500 km/s, more than enough for the job. In the process it will travel about 13 million light-years and have a final speed of 1 lightyear every 200 years.

 

[Nicodemus]

Fortunately there are several.

(1) Use big magnetic fields to channel the Solar Wind out one pole, thus turning the Sun into a rocket. The Solar Wind might be pushed to higher mass-loss rates and higher speeds, which Galactic escape will need. Just how fast? That's a bit tricky because of the Galaxy's Halo of mass - either Dark Matter or MONDian gravity - which means the Galaxy's effective mass increases as you move away from it. If we assume a maximum mass of ~1.2 trillion solar masses at a radius of ~150 kly, then the escape velocity is ~474 km/s. Our Solar Wind rocket would need a fast Solar Wind (say ~950 km/s) to eject about ~40% of the Sun's mass to push it to that speed.

(2) Surround the Sun with a perfect reflector to one side - thus creating a giant Photon rocket. Over the next ~5 billion years the Sun will produce enough light-energy to propel it to a speed of ~152 km/s. Not quite enough. So we need to up the luminosity. If we coaxed it to fuse all its hydrogen, instead of just ~10%, then we'd be pushing towards 1,500 km/s, more than enough for the job. In the process it will travel about 13 million light-years and have a final speed of 1 lightyear every 200 years.

I like those ideas, but that seems more like sending a star on a "ballistic" journy, not really moving it to another location. The concept of how you go about the process of braking boggles the mind, but I suppose if some exotic form of life were bound to ONE star.

Hey, maybe it would be better to slingshot Jovian planets into it, and combine your rocket idea AND give it more fuel to work with. You could impart a little momentum too, and that might allow you to preserve some luminosity for later.

 

[FtlIsAwesome]

Check out the http://en.wikipedia.org/wiki/Stellar_engine" on Wikipedia. It is a megastructure capable of moving a star by redirecting its radiation, and therefore generating continuous net thrust. Though it is very slow. It'd take a billion years or so to leave the galaxy. It can be combined with the Dyson sphere concept to gather usable energy. Also, the engine can direct it to slingshot around other stars repeatedly, which would probably cut down the travel time significantly.

I'm curious, why do you want to eject a star? A form of intergalactic travel? (A habitable planet can orbit the star. It wouldn't have some of the problems of an interstellar or intergalactic spacecraft .)

 

[mistergrinch]

See this story: http://www.dynamical-systems.org/zwicky/Essay.html

It's based on an idea of Fritz Zwicky for moving the sun by firing pellets into it to produce asymmetrical fusion explosions, which he thought could move the sun to Alpha Centauri in 2500 years!