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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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    $\begingroup$ You don't need a cluster of them. One will do: en.wikipedia.org/wiki/Gliese_581_g $\endgroup$
    – Zo the Relativist
    Dec 8, 2011 at 0:46
  • $\begingroup$ Lots and lots of question..... :P $\endgroup$
    – Vineet Menon
    Dec 8, 2011 at 8:37
  • $\begingroup$ @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. $\endgroup$
    – Charles Teague
    Dec 8, 2011 at 18:08
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    $\begingroup$ 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. $\endgroup$
    – user2963
    Dec 15, 2011 at 18:03

2 Answers 2

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The orbits of the stars will be inherently unstable. Gravitational systems with more than two bodies exhibit chaotic behavior, known as the (N-body problem). Even the Solar System is unstable in the extremely long term.

The heavier the bodies and the closer they are, the more gravitational energy is exchanged with each orbit. Any starting arrangement of a dozen stars within the orbit of mercury would result in most stars being ejected, and perhaps some spectacular collisions.

The gravity of a binary star is approximatly a point source from much further away, enabling longer-lasting multiple star systems. Trinary systems have a third star orbiting a binary from a distance, while a quaternary system may have two binaries orbiting each other. The record for the number of stars in an hierarchical arrangement is 7 according to NASA (accessed Feb 2023).

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  • $\begingroup$ Your own wiki link shows known systems up to 7, so 5 is not the record so far. $\endgroup$
    – Jerry B
    Jan 28, 2018 at 11:15
  • $\begingroup$ @JerryB Difference of record might have to do with that post being 6 years before your comment... and another 5 to mine :) That Wiki link currently lists up to "Novenary" systems, although upon cursory reading, articles linked as such systems seem to describe pairs of pairs in detain (maybe with more partner stars assumed but not visible?) $\endgroup$
    – Jim Klimov
    Feb 8 at 9:41
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    $\begingroup$ @JimKlimov • Wikipedia has a "View History" function. As of 27 Nov 2011 (18 days before the post by Graham), the page already showed a septuple system. Indeed, it had been there since 27 Aug 2009. • Meanwhile, some have considered Mizar & Alcor to be a likely septuple since at least June 2002… • As for QZ Carinae, the Multiple Star Catalog lists it as having 5 components, and the footnote for it on that wiki page says 4. It may well be misclassified on that page. • MSC reference: ctio.noirlab.edu/~atokovin/stars/… $\endgroup$
    – Jerry B
    Feb 9 at 15:58
  • $\begingroup$ Updated to NASA page stating 7 stars. Looking at the star catalog and the QZ Carinae paper, it may be that "9 components" in the paper refers to the vertices in the graph, which shows 5 stars. It is confusing. $\endgroup$
    – Graham
    Feb 9 at 16:43
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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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  • $\begingroup$ 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. $\endgroup$
    – Charles Teague
    Feb 25, 2014 at 2:13
  • $\begingroup$ That would indeed extend the lifetime. And if you can do that once, you can go in later and pull out the helium again, while topping up the hydrogen. In theory, you could extend a star's life up to the Big Rip (if that turns out to be real). en.wikipedia.org/wiki/Future_of_an_expanding_universe $\endgroup$
    – Jerry B
    Jan 28, 2018 at 11:42

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