"Bjoern Feuerbacher" <feuerbac@thphys.uni-heidelberg.de> wrote in message
news:cjufs5$p0e$1@news.urz.uni-heidelberg.de...

Grey Knight wrote:

Thought that subject line would get your attention ^_^

I'm writing a sci-fi book in which one of the plot elements is a bunch
of aliens "modifying" a star to turn it from a G5 (yellow main seq)
into an M3 (red giant).

Sorry, but AFAIK, an M3 star is *not* a red giant. It is a red star
- but it is on the main sequence, like our sun, and even smaller than it!

So, please specify what you want - a M3 star, or a red giant? Apparently
the second...

In your humble opinions, what would be a
plausible (Well; don't worry too much, it IS fiction) method for this
to happen?
NB: references to "making the star think that X" are figurative ;)

(A) "Siphoning off" hydrogen via a wormhole, making the star think it
is in the helium-burning stage

Well, you had to "siphon off" the hydrogen from its center (since there
both the hydrogen and helium "burning" takes place, so "siphoning off"
hydrogen from the outer layers won't help).

Unfortunately, that would also reduce the total mass of the star, and
IIRC, there is a lower limit on the mass, under which a star won't become
a red giant. So you have to pay attention that you don't "siphon off" to
much hydrogen... ;-)

So I would recommend that additional to the "siphoning off" of hydrogen,
you also add helium through the same wormhole!

(B) Applying some kind of gravitational effect to make the star think
it has a different mass

Probably won't work. I think the result would be a collapse of the star
and explosive helium burning, leading to a disruption of the star.

Perhaps if one were able to apply gravitational fields in a very
controlled, very specific manner, it *could* work - but sounds quite
complicated to me.

(masses submerged in this universe's
"slipspace" near the star could conceivably have such an effect?)

What's a "slipspace"???

(C) None of the above (specify a new idea)

Since a star becomes a red giant when a certain amount of the hydrogen in
its core has turned to helium, approach (A) above should work - provided
that not only hydrogen is taken out, but helium is added instead.

And how exactly will you remove the hydrogen directly from the core? Inject
a miniature black hole right in its center and then remove the blackhole
right after the hydrogen is sucked in? And how will you prevent the helium
from being sucked in?

And how exactly will you remove the hydrogen directly from the core? Inject
a miniature black hole right in its center and then remove the blackhole
right after the hydrogen is sucked in? And how will you prevent the helium
from being sucked in?

one way to do what you want would be to remove the central radiative
pressure that the burning core exerts on the atmosphere, while keeping
its mass there to cause the atmosphere to collapse. this means either:
a) stopping the core burning, b) preventing the energy caused by fusion
getting out or c) channeling it off somewhere else.

This is exactly what I have already proposed. You cool the core by firing
something cold into it. A neutron star will do.

There is no way you can do this.

ru <ru@no.spam.please.net> wrote in message news:<slrncm5i58.1ti5.ru@newred.gradwell.net>...

In article <73250d5a.0410050521.757696b1@posting.google.com>, Grey Knight wrote:

Thought that subject line would get your attention ^_^

I'm writing a sci-fi book in which one of the plot elements is a bunch
of aliens "modifying" a star to turn it from a G5 (yellow main seq)
into an M3 (red giant). In your humble opinions, what would be a
plausible (Well; don't worry too much, it IS fiction) method for this
to happen?

I see the confusion; the website I went to to look up spectral types
must have replaced roman numerals with arabic; hence GV -> G5 and MIII
-> M3. Tsk tsk. Yellow Dwarf to Red Giant is indeed what I intended.

The "slipspace" I referred to earlier, but didn't define, is the
common-or-garden subspace/hyperspace/whateverspace employed by scifi
writers since the dawn of time; this current incarnation is a
six-dimensional space (four spacelike, two timelike) which is probably
going to end up (in the final draft) being orthogonal to Minkowski
space rather than "underpinning" it as is more common. YGTI.

what happens (briefly) is that the core stop burning, and the radiative
pressure on the atmosphere stops balancing its weight. the atmosphere
starts to collapse onto the core, until a shell around the core gets hot
enough to start burning (i can't actually remember if this is helium or
hydrogen burning; there may well be hydrogen left over in the atmosphere
of the star after the core has used up all of its hydrogen; my old
lecture notes are at home ;-) ). this inflates the atmosphere, and the
star bloats up into a red giant.

one way to do what you want would be to remove the central radiative
pressure that the burning core exerts on the atmosphere, while keeping
its mass there to cause the atmosphere to collapse. this means either:
a) stopping the core burning, b) preventing the energy caused by fusion
getting out or c) channeling it off somewhere else.

I'm interested in this idea of simply removing the radiation pressure;
perhaps the aliens are siphoning off some of the *radiation* from the
core, tapping the star as an energy source? The outer layers of the
core would probably still remain hot enough to trigger helium burning,
since they manage it in a regular red giant.

This approach has the added advantage of giving a plausible *reason*
for the aliens' actions; I was worried about that for a while ^_^ I
only really came up with it because I liked the idea of some little
green Laurence Llewelyn-Bowen going "Oh, that star isn't really very
nice looking; let's tinker with it a bit."

I remember from my stellar physics classes that, what with all the
collisions, photons generated in the core take some incredible number
of years to escape (compared to eight minutes from the Sun to Earth!);

given that, how long could we expect the aliens to be siphoning off
photons before the star begins to swell noticeably, and how long would
the expansion take once it starts? (assuming reasonable figures for
star's mass, percentage of photons siphoned, etc)

If the aliens were
to change their minds, could they reverse the process by cutting the
wormhole?

If not, how else could they reverse it? How long would that
take?

ru <ru@no.spam.please.net> wrote in message
news:<slrncm5i58.1ti5.ru@newred.gradwell.net>...

In article <73250d5a.0410050521.757696b1@posting.google.com>, Grey

Knight wrote:

Thought that subject line would get your attention ^_^

I'm writing a sci-fi book in which one of the plot elements is a bunch
of aliens "modifying" a star to turn it from a G5 (yellow main seq)
into an M3 (red giant). In your humble opinions, what would be a
plausible (Well; don't worry too much, it IS fiction) method for this
to happen?

what happens (briefly) is that the core stop burning, and the radiative
pressure on the atmosphere stops balancing its weight. the atmosphere
starts to collapse onto the core, until a shell around the core gets hot
enough to start burning (i can't actually remember if this is helium or
hydrogen burning; there may well be hydrogen left over in the atmosphere
of the star after the core has used up all of its hydrogen; my old
lecture notes are at home ;-) ). this inflates the atmosphere, and the
star bloats up into a red giant.

one way to do what you want would be to remove the central radiative
pressure that the burning core exerts on the atmosphere, while keeping
its mass there to cause the atmosphere to collapse. this means either:
a) stopping the core burning, b) preventing the energy caused by fusion
getting out or c) channeling it off somewhere else.

I'm interested in this idea of simply removing the radiation pressure;
perhaps the aliens are siphoning off some of the *radiation* from the
core, tapping the star as an energy source? The outer layers of the
core would probably still remain hot enough to trigger helium burning,
since they manage it in a regular red giant.