A Note on Mira's Companion
Mira and its companion orbit with a period of about
400 years. The one source I could find that contained any data on
the matter specified that Mira and its companion are about 70 AU apart.
It is not clear whether this figure represents the periastron or the
apastron distance or just an average.
Suggestions from several sources indicate that Mira and its white-dwarf companion
have an at least partially symbiotic relationship as the white dwarf does
seem to be accreting matter from Mira. Whether the matter is being
drawn from Mira's distended surface as indicated in this essay or is simply
being collected from dust and gas cloud that surrounds Mira is never made
clear, and probably is not actually known. In addition, I have not yet found
any indication as to whether the accretion goes on only when the stars are
in relative proximity or if there is enough matter even at 70 AU (or whatever
the apastron distance is) for any significant accretion to take place. In
the illustrations for this essay, I have only shown visible evidence of accretion
when the white dwarf is quite close to Mira (Yes, I am aware that I probably
made the accretion disk WAAAAAY too small). In considering some of
the Hubble Space Telescope images of Mira, it seems possible that the two
stars really do come fairly close to each other, possibly close enough for
the white dwarf to drag material from Mira's outer layer. The dwarf
is sometimes even brighter than Mira, and it is known to flare on occasion.
I have taken the liberty of depicting the orbits of the two stars as such
that the two stars are, perhaps 15 to 20 AU apart at periastron when
both are on the main sequence, and that, as the stars evolve, their orbits
have decayed, the stars spiralling in toward each other until, by the time
Mira is in an advanced stage of gianthood, they have devolved to a point
where the periastron distance is as little as 3 to 5 AU. I have no basis
in science for such a decay other than the idea that (though their masses
decrease as they blow off their outer layers into space), the stars tendency
to move farther apart is more than counteracted by frictional drag imposed
by the matter ejected into surrounding space first by Mira's companion and
then by Mira, itself as they evolved.
It is hoped that this "bending of the rules" will allow the orbits
of the two hypothetical worlds depicted in this essay to be considered as
at least remotely possible. It is understood that planetary orbits
about one star in a binary system with radii greater than 20 to 25% of the
periastron distance between that star and its companion would be disrupted
by the companion star, and the planet either jettisoned from the system
or plunged into its sun. While this wouldn't be a problem during the
time that Mira and its companion are on the main sequence, it would become
a problem should the stars move closer together when they evolve off the
main sequence. Several of the depictions as viewed from the outermost
planet would therefore be somewhat unlikely since that planet is orbiting
its primary at a distance of about 5 AU, and Mira's companion is clearly
close enough to Mira to pull away some of its atmosphere into an accretion
disk (and in one case, actually appears to be below Mira's outer layers (Stage
18). Perhaps, therefore, we can consider this planet to be in iminent
danger of being thrown out of the system (or into Mira) as its orbit is
disrupted.
I attempted to compensate for this in the later stages (19 through
22 or so) by having this planet depicted as spiralling in to Mira. However,
the planet is destroyed (Stage 23) before it ever has a chance to fall
completely into its sun.