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So, I was watching various sci channel shows, and they touch on how extremely massive stars live only 100k years, vs the sun which lives ~10 billion years, and dwarf stars live some unspecified time longer.

So, lets say you have a galactic civilation, worried about "heat death", and in order to avoid it, they decide to take apart a number of large stars, making them into a cluster of dwarf stars, so the star will take much longer to burn out...

First, can a group of dwarf stars orbit a common center, close enough that we can considering their combined luminosity as a unit? maybe if we can get them all within the orbital distance of mercury from the common center? Not sure how stable orbits would be once your talking a dozen or more objects?

Second, how much luminosity loss is there? Say you have a combined cluster of 20 dwarf stars, each 1/20 of the mass of the sun, and all within a sphere of mercury's orbit? How much lower would the combined luminosity be -- and so, how much closer would earth have to be in order to maintain liquid water? I'd guess you'd still have some extreme seasons as you made closest approch to any one dwarf.

Third, if we know how close earth would have to get -- could there be a stable orbit around such a cluster, at that range?

Finally, if you can do all that, do you really get much added time? Assuming the source star was halfway thru it's main sequence when split into the cluster of dwarfs, so I guess you'd be estimating the remaining lifetime of a dwarf star (each 1/20 of a stellar mass), which is halfway thru its main sequence?

Edit: Since this is such a multi-stage question: if we know we can refute something right away (ie: perhaps you cannot have a dozen dwarf stars in any stable orbit unless they are very far apart), that could end the issue right away.

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You don't need a cluster of them. One will do: en.wikipedia.org/wiki/Gliese_581_g –  Jerry Schirmer Dec 8 '11 at 0:46
    
Lots and lots of question..... :P –  Vineet Menon Dec 8 '11 at 8:37
    
@Jerry: I was thinking that you would have an existing star system with a stellar mass star as the starting point. But its probably way less effort to move a planet into place around an existing dwarf, than it is to "peel apart" a star into several dwarfs. –  Charles Teague Dec 8 '11 at 18:08
    
if you're able to arrange something like that in the first place, you probably don't care much about what our science says is stable and unstable. –  user2963 Dec 15 '11 at 18:03
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You have the answer in the edit - the dwarf stars orbits will be unstable. Gravitational systems with more than two bodies are inherently chaotic (N-body problem). Even the Solar system is unstable over the long term.

The heavier the bodies and the closer they are, the more gravitational energy can be exchanged. You will find stars being ejected all over the place.

There is a "very far apart" limit: for example multiple star systems like a trinary system where two stars are very close and the third one is far out orbiting the central pair like a planet, or two pairs widely separated so that the other pair is approximately a point source. The record so far is 5 stars.

To do that with a dozen stars would take a lot more space than the orbit of mercury. If you tried, you would find singles and pairs being ejected at random and maybe even get some spectacular dwarf collisions.

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I agree with Graham's answer and to add to that, another problem with this setup however, is that for a planet to be in an approximately stable orbit, it would have to be much further away than the orbit of the most eccentric star and that distance would definitely lie beyond the habitable zone.

You don't need a cluster anyway. You can just put a planet around a normal dwarf star and have it much closer in than we currently are. Greenhouse gases play a massive role in the temperature too.

A 0.1 solar mass dwarf will last for 3 trillion years. http://www.wolframalpha.com/input/?i=+1%2F10+solar+mass+star and a massive star (~10Mo) lasts for about 30 million years on the main sequence.

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thanks! so, if you could convert a sun-like star with only the last billion years left in it, into a dwarf, somehow, presumably keeping the hydrogen and getting rid of the heavy stuff, you WOULD at least get a huge increase in longevity. –  Charles Teague Feb 25 at 2:13
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