Create a star

[Ziggy Stardust]

This is a random hypothetical question inspired by a news item (admittedly, it's an old one) that I stumbled across. Link. For whatever reason this just got me to thinking: assuming that what scientists presently theorize about the 'birth cycle' of stars, what sort of technology would be required to actually create a sun?

The current theory (I don't know too much about astronomy, so I don't know how much evidence has been accrued in support of these theories, but I am going to take it for granted, for the sake of the hypothetical, that they are accurate) is that clouds of molecular gas "collapse" after reaching a certain critical density and temperature, which makes them unstable. Over the course of several hundred thousand years, rotating spheres of superhot gas form, and fusion of deuterium begins. After a long period of time (I can't find an exact figure), if the star gets hot enough, hydrogen fusion occurs, and the star rapidly becomes stable and main-sequence. This is a very brief, lay overview of the initial stages in the birth of a star; hopefully some of you will know more about the process.

Anyway, it takes millions of years for the transition from gaseous cloud to main-sequence star. Assume some advanced future civilization that, for whatever reason, has unlimited resources devoted to this project, wants to create a star (that will be similar to our Sun). What sort of technology would they need to actually do it? For example, would they develop something to accelerate globs of superheated matter at near-light-speed into clouds of gas creating supersonic shock waves that begins a chain reaction leading to collapse, (from here)? Or would there, given sufficient technological might, be a simpler way of doing things?

And, here's the clincher: how much technology/resources would be needed to not only initiate creation, but to create a fully formed main-sequence star within a single human lifetime?

[Ender]

Lots of ram jets and a few million years. Deploy ram jets outside nebula. Use ram jet field to push matter forward as you go rather then collecting it. End result is just accelerating the natural process.

To do it in a human life time? Some kind of time dilation machine to extend the life of the human.

[Kanastrous]

To do it in a human life time? Some kind of time dilation machine to extend the life of the human.

[Patrick Degan]

Lots of ram jets and a few million years. Deploy ram jets outside nebula. Use ram jet field to push matter forward as you go rather then collecting it. End result is just accelerating the natural process.

You could also use the ramscoops as collectors, only in this application the nebular material is directed instead toward a common core point defined by the positions of the scoops. You could have a large asteroid in that position as a gravitational "anchor" (yes, the specific gravity of the body would be infinitessimal even in comparison to one of the smaller moons, but enough to act as an initial building block, so to speak).

[Zixinus]

Create a box made out of forcefields the size of a small nebula. Trap enough interstellar dust to create a sun. Push box of forcefields into being smaller, until the nebula starts to gather by itself.

Use super-hyper-oh-shit-that's-strong laser, nukes or something to occasionally heat things up if you need to.

Then again, I've read that you need a certain type of dust and density for thing to heat up properly, as if there is too much contact then the a choke-point will conducts its heat away.

Granted this is the kind of technology that would make even people from Star Trek or Star Wars wet themselves. In concert.

You can also make an uber-powerful gravity engine that pulls interstellar dust towards it. If it can gather up enough, the fusion process might start by itself, although with the destruction of the machine.

All this within a human lifetime? Make the human life long. Very, very, very, very, very , very ,very long.

[Patrick Degan]

All this within a human lifetime? Make the human life long. Very, very, very, very, very , very ,very long.

Easily enough done. Your crew of engineers will need to periodically check the progress of the collection operation, so put them in shifts on relativistic shuttles. As one group comes in, the next one heads outward, accelerating to a high fraction of c. and cruising for a year or two relative.

[Zixinus]

Actually, if you can make several uber-powerful gravity generators that create anti-gravity as well as gravity and place them well, you can compress the star's nebula even faster. You'll most likely first get a hot pocket of gas and then you have to work your way up until . You might even want to manipulate the hot pockets as well.

You might speed up the process even further by starting or helping the fusion process yourself by nukes or the mentioned gravity generators to create some sort of collecting effect at the core of the star.

[Kuroneko]

Inputing thermal energy, through nukes or otherwise, is absolutely the last thing you would want to do if your task is to speed up stellar formation. The colder the gas is, the faster the star will form.

A spherical molecular cloud of solar mass and, say, average molar mass of 2.5g/mol [1] and average density of 1e6 particles per m³ [2] would be about 5 light-years in radius. Newton's law r" = -μ/r² has the solution r = R/2(1+cos θ), t = (R/2)sqrt(R/2μ)(θ+sin θ), where R is the orbital apogee, so that even if all thermal energy is pseudomagically removed so that the cloud can freefall as dust rather than as collapse as a fluid [3], the time it would take for the matter at the midradius R = 2.5ly (μ = 1.5e19 m³/s²) to contract to half that (θ=π/2) would be about 27 million years.

Although roughly uniform density is probably not at all realistic, it still establishes the scale even under ideal thermal conditions (T = 0) as millions of years. Anyone interested could run the calculation again for different parameters and even a non-uniform initial density distribution (this would just change how μ at a given radius is calculated), but it is clear that massive speedup of the degree required is impossible without magic or a loophole of the type Ender proposed.

[1] I'm not at all sure what the typical compositions of such things is--molecular hydrogen would of course be about 2.0g/mol, but the cloud would also contain heavier elements and molecules.
[2] This is probably on the dense side.
[3] Naturally, this would be the fall of the Ziggy stardust.

[Aquatain]

Find some Aliens and begin to chant"..The rain in Spain stays mainly in the plain.."..

[Zixinus]

Since we are already manipulating time and space in some of our exemples, there is also the idea that you can create a pocket-dimension (or whatever) in which you use machines to do the process. Time in that area is sped up several times, so you can have the ability for the star to properly form and do it under one human lifetime.

[starslayer]

As Kuroneko said, you don't want to add much energy to the cloud. It turns out that there are clouds in nature that collapse too fast, heat up too much, and blow themselves apart. You may be able to counteract this somewhat by adding a surprising chemical: water. According to an article in Astronomy magazine I read some years ago, there is evidence that in order to form stars like the Sun, slightly wet clouds do a far better job, simply because of their higher heat capacity, which prevents the molecules from acquiring too much kinetic energy and flying apart. In any case, speeding up the process by many orders of magnitude seems a pipe dream, even for a civilization with SAT (Sufficiently Advanced Technology). However, as others have noted, if we can exploit relativity, this becomes fairly easy.

[Omeganian]

You'll need to invest a lot of energy into accelerating. And then find some way to bleed off the excess energy. Depressing.

[Xon]

To do it in a human life time? Some kind of time dilation machine to extend the life of the human.

A single Xeelee Nightfighter from Stephan Baxter's Xeelee Sequence condenced a cloud of atomic Hydrogen into a star and then artificially induced fusion to the levels to create a Earth-sized planet in six months.

But the Xeelee are right up there in technology which manipulates the structure of space/time.

[RedImperator]

Since we are already manipulating time and space in some of our exemples, there is also the idea that you can create a pocket-dimension (or whatever) in which you use machines to do the process. Time in that area is sped up several times, so you can have the ability for the star to properly form and do it under one human lifetime.

Why don't you just wave a magic wand and say "Abracadabra!"? Ooh! I know! Let's have zillions of teeny-tiny fairies carry individual molecules to one place. Or if that doesn't work, we'll remodulate the deflector dish to salt the nebula with subspace stellagenic particles. And if all else fails, we'll just catch a leprechaun and make a wish.

Come on. When someone says, "How could X be done?", presumably he wants an answer that requires some thought. He could just make up imaginary physics-busting technology on his own.