Celestia Forums

Death of a Giant: Layman's guide to stellar evolution
http://mira.lafeyette.net

While the images weren't created for or with Celestia, this guide may come in handy for those interested in creating suns (and worlds) with a mind to the latter stages of stellar evolution.

If you have any questions or comments, please drop me a line!

NOTE: Content of the Stellar Evolution site is entirely my fault. No stars or persons were intentionally harmed during its creation.

NOTE2: Yes, I know the stellar cut-away view diagram is missing. I'm workin' on that. In the meantime, please enjoy the animated Stellar Evolutionary HR diagram!

NICE. I've never really paid much attention to Mira before, but this was a very fascinating journey. I'd love to see something similar for Sirius!

Well done.

...John...

Well, John, you're in luck! Mira and Sirius are both binary systems, where one of the partners is already a red dwarf. Sirius is about 2.2 times the Sun's mass, while Mira is somewhere between 2.2 and 3.7 solar masses. So, given that, the pictoral essay you just looked at should be about as accurate for Sirius's future evolution as it is for Mira, though the time-frames for Sirius will be somewhat longer due to the star's smaller initial mass.

With regard to Sirius's position on the Mira essay timeline, you could take Sirius, itself to be at approximately the point mentioned at Stage 2 or 3, and its companion star to be at the position depicted roughly between Stages 4 and 5. The discrepency between the relative stages is because the time-frame between the final evolution of Mira's companion to white-dwarfhood and the start of Mira's evolution off the main sequence is depicted as being shorter than it probably was for Sirius and its companion. In other words, Sirius's companion was probably substantially larger and more massive than Sirius is, and so completed its evolution off the main sequence before Sirius began to even leave the main sequence. In the case of the Mira system, I assumed the two suns to be relatively close to the same mass, and thus that they would evolve off the main sequence at relatively close times. My assumption, of course, could be wrong, but the photographic and reported evidence I have seen suggests that I am right.

One thing that may be of interest to you regarding Sirius is that the star was described as being reddish or orange in ancient texts dating back a few thousand years. Whether this was due to the white dwarf companion still being in the stage of red giant (doubtful. I doubt that a star could evolve from AGB giant to white dwarf in only 5000 years) or being in the final stages of blowing off a last ring of un-burnt hydrogen (more likely--hence my suggestion that the companion might be in the state depicted in Stage 4 of my essay) is not made clear.

.... Stage 11 probably most closely approximates the present evolutionary status of Sirius and its companion. Taking the "Mira" presentation from there onward should give you a pretty good idea of what the future holds for Sirius, though, as I have said before, the time-frames are different--longer for the less massive star than specified (for Mira). In fact, you could use this presentation for just about any sun-like (binary) star (ignore the white-dwarf companion for those stars that don't have such, or where the binary companion is less massive and less evolved than the star of interest.)

A.

Thanks for the info! Sirius has always interested me in so far as stellar evolution goes. Another star that I have a great interest in, though from a fictional setting stand point, is 40 Eridani. The A star is theoretically a "habitable" star, and the system is certainly old enough to have a world with a mature biosphere. But the kicker is the presence of a white dwarf. Although located substantially far away, I have to wonder what effects this white dwarf would have had on the young system, when the star was evolving off of the main sequence and going through its red giant phase.

As for Sirius, I think it has been comfortably proven that the Greeks likely didn't see a truly red Sirius. More than likely, this allusion was in reference to the shifting of its light towards the red during its rising, or even (and probably more unlikely) a reference to it somehow being an unlucky star. But most interestingly, there are apprently other references out there, dating from roughly the same time, in which Sirius was referred to by its more familiar color.

Neat stuff!

...John...

Here's a page about Sol's death. It has Venus and Earth survive because of Sol losing mass causing their orbits to enlarge.

http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html

Interesting. Most studies I've seen, however, suggest a lower mass-loss proportion and rate during the sun's RGB stage. Further, they suggest that during the Sun's RGB phase, it will only expand to about the size of Mecury's orbit (and will destroy Mercury). It is suggested that the major portion of the mass loss will occur during the sun's stint on the AGB branch, mostly in the "four final pulses'. While there is still some question as to whether the earth will escape incineration within the sun's outer envelope, the article you cite is the first one that suggests that Venus will survive. Every other source I've seen indicates that Venus will be consumed as the sun expands to about two AU in diameter (slightly more than 100 times its present diameter) during its AGB phase.