Build Our Own Star?

Factual Questions
21

A few quick things.
T Tauri stars: While not well understood, it is generaly believed their energetic behavior has a lot to do with how they are born. Stars form out of large clouds with their own magnetic fields and rotation. When you shrink a big cloud to a little star, it is like a figure skater pulling their arms in a spin, they speed up. The same is true for both the star rotation and the magnetic field (conservation of angular momentum and magnetic flux for the physics minded). Theorists have long known that this was a problem for forming stars at all. Stars need to get rid of this extra spin and magnetic field and we think this is what all this violent early activity is about. It is not clear to me that tossing ten brown dwarfs together will have an effect at all similar.

Restarting our sun: Our sun only uses 10% of its fuel over its lifetime. The problem is all the burning takes place in the core, which fills up with helium (which does not burn in our sun). If we could mix the sun (and probably regularly remix the sun) we might make it last 10 times longer. That, however, might be harder than moving a brown dwarf.

Moving a Brown Dwarf: Hold on, because I’m going throw a little matha t ya. A really powerful solid fuel rocket (say a Proton) can produce about two million Newtons of thrust (a Newton can accelerate 1 kg by 1 meter/second per second.) Ion rockets are 10 times more efficient, so in the distant future we can probably imagine one producing 20 million Newtons for the same price/size. Now lets build one million of them and send them to the nearest Brown Dwarf for a total of 20 trillion Newtons of thrust (2x10^13 N if you like).
Sounds impressive, and it is, but Brown dwarfs are big. At 1/20 the size of our sun, that is 10^29 kilograms (a hundred thousand trillion trillion…from this point on I might have to stay with scientific notation). Newton’s second law says that Force = Mass x Acceleration. Using out million futuristic Proton rockets on our Brown Dwarf gives an acceleration of 2x10^-16 meters per second per second, or 0.2 femtometers per second per second.
But we have a long time right? Say all 20 of our brown dwarfs are spread out over a sphere a light year in radius. To simplifiy things, say we need to move the typical brown dwarf a half light year to get it to the joining spot (it would be slightly longer). That is about 5x10^15 meters. If
our million rockets were firing the entire time, how long would it take it to get there?

100-200 million years.                           (distance=0.5xaccelxtime^2)

Unlikely any technology could work that long. One could be clever and look for brown dwarfs that were heading in a similar direction, which could certainly cut the necessary time down, but I think you see the problem. I would much rather hook those same rockets to a good sized asteroid and cruise my population to the next star…

But that’s just me.

22

If the sun engulfs the Earth’s orbit, how long would it take before it engulfs the orbit of Mars? Is there any percentage in terraforming Mars in anticipation of the day the Goldilocks Zone reaches it? What about other (non-gas giant) planets?

23

Well, I was envisioning something much more like what somebody proposed for increasing the radius of earth’s orbit - put something else in orbit and slowly tugging it out.

So the technology I’m envisioning that would last as long as needed would be an orbit - which, I believe, can last that long.

First, I’m relatively certain that the thing about the sun actually engulfing earth has been found to be wrong - the sun will be much less massive by then, and won’t swell up to an earth orbit size.

However, it is going to be darn hot.

Anyway, your question is still valid, but I’ve assumed that by the time we’re talking about, all the inter-solar-system colonizing possible will have already been done, and it’ll be crowded too.

24

ULIRG – Great first post!! Welcome to SDMB; you’re a definite aset!

I appreciate the correction on the T Tauri – in my layman’s minimal knowledge, I was under the impression that the flares in the T Tauri stars resulted from their undergoing stabilization as they lit up.

Re: bup’s last post – does anyone know the most recent estimates for how much the Sun will expand as it enters giant phase? Whatever it is, I’m certain the increased insolation will be sufficient to make Earth uninhabitable at its present orbit, even if it doesn’t reach out to and incinerate it.

For all practical purposes, the Sun will not be significantly less massive at that point. H>He Fusion only reduces mass by something like a thousandth of a percent; the solar wind associated with the Sun is fairly minimal compared to stars that do lose substantial mass by solar wind. A percent or so reduction over a multi-million year span, I can believe; a sizeable mass reduction, no.

I see your point about getting a brown dwarf to move towards another one by altering its orbit – but how do you propose to do that? You’d need to move something as massive to gravitationally do so, and see ULRG’s post on using thrusters.

25

As far as inhabiting the Solar System during the Red Giant phase without stellar engineering -

the comfort zone with Earth-like temperatures would be at about 40 AU - round about where Pluto is now, but due to a strong stellar wind the Sun will lose a lot of mass, so perhaps Neptune and Uranus will migrate into this temperate zone.

The Earth itself won’t be engulfed directly as far as I can make out, but it would be entirely uninhabitable. It might get braked by the solar wind and fall into the Sun, flaring like a meteor.

26

Long before the sun goes to the red giant phase, we’re going to have to do some cosmic engineering.

You see, as main sequence stars age, they heat up. The newborn sun, after settling down to main sequencehood, radiated only about 70% of what it does today. In something like .5 to 1 billion years, it will heat up so much that it’ll roast the surface of the Earth. So what we need to do is start planning on moving the Earth away from the sun.

Sometime in the next couple hundred million years, we’ll have to put those plans into effect. And then every couple million years, do it again. So by the time the red giant phase comes, the Earth should be far enough away not to be incinderated.

But don’t get overconfident here. Red giant phases are quite short compared to the lifetime of a star. And after that comes the white dwarf phase, and who wants to orbit one of those tacky things? I mean gauche doesn’t even begin to describe the experience.

So it will be incumbent on us to find a new star at that point. Perhaps a nice G8 or K0 would be good. They last much longer than the G2 we have now.

27

am I the only idiot who opened this thread thinking it might be about selecting a famous Doper from among the posters here and making him the “Star” of a TV show?
But at least now I’ve learned that stars can be catergorized as types O and A., just like blood samples.

28

There is a couple of Science Fiction novels called “The Mechanical Sky” by Donald Moffit that indirectly addresses this issue. In these books they whip stars around like billiard balls around a table by creating fast moving black holes and doing close flybys of the star, captuing the sun and dragging it along behind the BH. I always thought there was a few problems with the physics, but the idea was nice.

DancingFool

29

Okay, you’re willing to plan sufficiently far ahead to move a Yellow star’s equivalent in mass around, gather them in one place, and wait for the resulting star to stabilize. Let’s assume we have all the questions about internal stellar structure and isotopic composition (which might not be quite the same in a star created from substellar masses as for one that was naturally accreted with a higher percentage of the heavier elements residing [for reasons that elude me at the moment] in the planets).

It seems to me that you still need interstellar travel. Stars aren’t like batteries, you can just pop out the old one and pop in the new one. If there were two stellar-sized masses in our solar system, they would affect each other quite severely. The graviational influences are obvious, as are the radiation influences (i.e. each star would be destabilized, probably catastrophically, by the radiation from the other) The radiation from supernovas can influence stars tens or hundreds of light years away. We’re talking about putting two yellow stars that didn’t co-evolve within light hours or minutes of each other!

If we’re planning that far ahead, why not use the same unspecified technology we’d use to move gas giants to move our star and planet (and maybe a few other Solar planets, too, if we’re feeling sentimental) toward a younger, suitable yellow star? Our entire population could cruise in comfort for a million years or a billion, like a retiree in his Cadillac land-yacht or RV, with scarcely a though that their were en route to a destination.

Then, when we near the target system at a distance of a few light years (obliquely, above the planetary plane), we spend a few centuries abandoning Earth like fleas off a bathing dog. Sol could then sail off into space, where it won’t upset our new home.

We could even fly Earth into orbit (if we can tolerate a few decades or centuries of planetwide “Are we there yet?”) in that pesky intra- system interval of several years without a convenient warming sun required since we can’t allow the old and new suns to approach too closely or for too long. That would probably be a button-down bear to sit through (and wreck the planet), but at least the transport ships we’d need would only be interplanetary, and we could always go back to Earth for anything we forgot - assuming it wasn’t frozen and destroyed during the inter-system transit (i.e. don’t expect to go back for any rainforest pharmaceutical plants you forgot to pack)

Of course, if we could do that, we could much more easily manage high relativistic velocity “wagon trains” to the stars (mass-produced ships with capacities from tens to thousands, with an admittedly uncertain survival and ultimately successful colonization rate) and simply do a stellar diaspora with trip-times in the range of years (in the ships frame of reference). Acceleration could provide us with a gravity equivalent (the ships could ramp up slowly to 2 gees or more, giving the crews time to acclimate). Time dialation would do the heavy lifting, Cecil’s skepticism be damned!

Of course, there’s the question of fuel, bu elementary math shows that this was a showstopper in any case. It’d take much more than a star’s total energy output to move it (or a pair of brown dwarfs) an interstellar distance in ten billion years. In fact, it would take more than the sun’s total energy output to move Jupiter stably from from one end of solar system to the other in a million years.

30

[QUOTE]
*Originally posted by KP *
**Okay, you’re willing to plan sufficiently far ahead to move a Yellow star’s equivalent in mass around, gather them in one place, and wait for the resulting star to stabilize. Let’s assume we have all the questions about internal stellar structure and isotopic composition (which might not be quite the same in a star created from substellar masses as for one that was naturally accreted with a higher percentage of the heavier elements residing [for reasons that elude me at the moment] in the planets).
**[\QUOTE]

The terrestrial planets (Mars, Earth, Venus, Mercury) are composed of heavier elements than the sun because when they formed they were not massive enough to hold onto Hydrogen and Helium. The outer planets, especially Jupiter and Saturn, are almost identical to the sun in composition (The density of Saturn is, in fact, significantly less). The sun has lots of iron and nickel, etc., but they are just dwarfed by the quantity of Hydrogen and Helium.

**

[QUOTE]

If there were two stellar-sized masses in our solar system, they would affect each other quite severely. The graviational influences are obvious, as are the radiation influences (i.e. each star would be destabilized, probably catastrophically, by the radiation from the other) The radiation from supernovas can influence stars tens or hundreds of light years away. We’re talking about putting two yellow stars that didn’t co-evolve within light hours or minutes of each other! [\B][\quote]

An extra star would have serious consequences for the stability of the solar system, but would actually only have a minimal effect on its companion star. The majority of stars are in binary or multiple star systems, some of which are extremely close (AUs, not light years). It is also quite common for stars to supernova right next to their companion without any significant effects of the second star, i.e. it is not blown apart. Turns out stars in the middle of their life spans are very stable. This doesn’t mean you can’t put two stars too close (stars can actually transfer mass this way, which doesn change them), but two G stars a light year apart would not be an issue.
As to the final fate of Earth, putting aside the issue of rising temperature (which might be a problem a lot sooner if we keep dumping CO2 into the atmosphere, but that’s another thread altogether), it is actually still an open question as to whether Earth will be engulfed by our sun when it swells up. The sun will actually swell up in two stages: The Red Giant stage and what is known as the Asymptotic Giant Branch stage (the naming has to do with how astronomers graph stars, but basically AGB is a second bigger Red Giant stage). Mercury gets fried in the first and possibly Venus as well (it is borderline for the old girl), while Earth will escape. Then, during the second stage, the Sun will start pulsing, swelling up and shrinking (and throwing off lots of gas in the process). Anyway, if Venus survived the first Red Giant stage, it is definitely cooked now while Earth may get hit by one of the brief “pulses” where the sun swells up enough to engulf the Earth. This probably dooms the rock, as there will now be drag as the Earth tries to continue in its orbit, which should pull it into the sun. Mars, on the other hand, should be fine, although again that’s not considering the temperature, just the survival of the planetary body. (from Rybicki & Denis, 2000, in the journal Icarus).

31

Boy, if I could ask this question a lot better now that everyone’s commenting.

My assumption was that we’ll have all kinds of technology, but not be able to break physics’ rule about breaking the speed of light.

Therefore interstellar travel would be possible, but would bite pretty hard. You’d avoid it if you could.

So, you build a star a few light months away - not light hours, not light years.

And you get to build it as you want - you don’t have to choose from the stars in our immediate vicinity. Build it right to G0 spec.

Then you pack everybody up, and get there in a few years. I don’t know if they travel on Earth, or stay in spaceships and ship Earth separately, or what.

Anyway, is that clearer?