nexium - Hi! Well, I am of the belief that "star differs from star in glory (1 Corinthians 15:41) in many, many ways - so there would be many varieties of brown dwarfs and red dwarfs, etc.<br /><br />I didn't have a specific variety in mind - I was wondering which variety at which speed and trajectory would most likely rejuvenate our sun [assuming future fine tuning] say some 5 billion years from now.<br /><br />I will respond to your model after I sleep on it and meditate about it. Meanwhile, here are a few facts about brown and red dwarfs:<br /><br />"Among stellar glow-worms, pride of place must go to the red dwarf RG 0050-2722 in Sculptor, with an absolute magnitude of 19. Some "brown dwarfs", such as the recently-discovered companion of Van Biesbroeck 8 (21 light years away) may be even feebler; their cores have never become hot enough for nuclear reactions to be triggered off." - "The World of Science," 1991, Vol.8, p. 24<br /><br />The latter type of brown dwarf would therefore have a higher percentage of hydrogen, since no significant hydrogen fusion had yet occurred. <br /><br />Another point is that our sun is on the lower mass end of main sequence stars:<br /><br />"Those of less than 0.08 solar masses never reach this stage [main sequence] at all, but merely go on shrinking to become first brown and then black dwarfs."- Ibid., p. 29.<br /><br />Meanwhile, if I (and you) am (are) correct, then our sun will become a low-mass main sequence star. Concerning low-mass main sequence stars, still over 0.08 stellar masses, the same source notes:<br /><br />"at the other end of the scale the low mass stars, if they evolve to the main sequence at all, will outlive the sun many times over."- Ibid., p.31<br /><br />So, I am not sure which would ultimately give our sun the longest lifespan:<br /><br />1. Continued mixing to a point where it becomes a low mass main sequence star with a much longer life span <br /><br />2. A brown dwarf collision-rejuvenation of our sun about 5 or 6 bi