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neilzero
2010-Feb-06, 12:30 AM
Assuming an advanced civilization expected their type G sun to go red giant soon, could they delay or weaken the expansion by injecting modest amounts of hydrogen into the sun's core slightly off center? It seems to me, that fusion would continue near the hydrogen injection site, even if the rest of the core was only helium, so their star would burn helium only in part of the core, thus reducing the size the star swelled to. If a Neptune mass planet hit the sun at 200 kilometers per second, would some of the hydrogen penetrate to the core of the Sun? How else might hydrogen be injected into the core of a type G or type K sun, assuming very advanced technology? A very fast (200 kilometers per second) neutron star, or solar mass black hole might pass completely though a star's diameter and keep going. Would hydrogen be injected into the core by the passage, besides the considerable hydrogen and helium that would follow the black hole out of the exit site. Would convection between the core and the rest of the star occur for perhaps days after the passage? I'm guessing the black hole would only gain about 1/10 th solar mass due to the 7 second passage though the star? How big would the exit hole be, very briefly? Neil

AstroRockHunter
2010-Feb-06, 12:48 AM
neilzero:

Remember, even though the core of the star is He, the bulk of the mass is still H anyway.

Could you please explain what your mean by
injecting modest amounts of hydrogen into the sun's core off center?

EDG
2010-Feb-06, 01:18 AM
A G-type star would be burning hydrogen in its core during its main sequence phase and converting it to helium (which would accumulate and form an inner core of non-fusing He). Once the core hydrogen is used up, the star enters its Subgiant phase when it starts to burn the hydrogen in a shell around the (now large) helium core. Eventually the helium core enters a degenerate state, and the star will enter the Red Giant Branch, becoming big, red and bloated. At some point though the degenerate core will itself ignite and helium fusion will begin (and then the star will shrink and enter the Horizontal Branch phase).

So really you want to be injecting the hydrogen during the main sequence phase, right into the star's core (around the "helium ash" inner core) if you want to prolong its main sequence life... though if you add too much mass then that might itself affect the evolution of the star.

neilzero
2010-Feb-06, 02:16 AM
Hi EDG: I agree, we don't want to run the experiment except as a last desperate attempt to delay the end of main sequence. Even a very advanced civilization likely can't evacuate even half of their population, so the alternative to the experiment is death for billions of people and loss of their property and goodies. Delay buys them time and reduced bloating means they can possibly survive in deep underground shelters, until the horizontal branch shrinks the star. Does repeated swelling occur as the core fuses nitrogen, oxygen, silicon etc? Does some convection occur during the horizontal branch, causing some additional hydrogen to be fused? Is there a reasonable probability for non-summitry of the fusing portion of the core? Slightly off center injection of anything into the core is likely to lead to at least brief non-symmetry of the fusing portion of the core and reduced energy output. Is there a possibility that no more fusion will occur after the hydrogen fusion ends with degenerate helium, if the swelling can be reduced sufficiently during the hydrogen fusing of the enlarged core branch? Is that what we think will be the fate of type M stars in the very far future? Is one million years each a reasonable estimate of the enlarged core branch, the first swelling and the first horazontal branch, for type G and K stars?
A type F Star could be pushed to neutron star, instead of white dwarf, but it is very unlikely we can add enough mass to do that to a G or K star. The neutron star or solar mass black hole experiment means a loss of mass at 200 kilometers per second, I think. Have you an opinion on a white dwarf or brown dwarf traveling the entire diameter of the sun, if impact speed is high enough? Neil

grant hutchison
2010-Feb-06, 03:07 AM
You need Rejuvenating the Sun and Avoiding Other Global Catastrophes (http://books.google.co.uk/books?id=AS_M2Gqtoj8C&dq=rejuvenating+the+sun+avoiding+other+global+cata strophes&printsec=frontcover&source=bn&hl=en&ei=h9xsS8TsHNHs-Aaos-H_Aw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBEQ6AEwAw#v=onepage&q=&f=false), by Martin Beech.

Grant Hutchison

DrRocket
2010-Feb-06, 04:50 AM
You need Rejuvenating the Sun and Avoiding Other Global Catastrophes (http://books.google.co.uk/books?id=AS_M2Gqtoj8C&dq=rejuvenating+the+sun+avoiding+other+global+cata strophes&printsec=frontcover&source=bn&hl=en&ei=h9xsS8TsHNHs-Aaos-H_Aw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBEQ6AEwAw#v=onepage&q=&f=false), by Martin Beech.

Grant Hutchison

Thanks for the reference. That looks like an interesting book. At $5.92, including shipping, it is pretty reasonable.

Van Rijn
2010-Feb-06, 07:31 AM
Here's an earlier thread on the same subject:

http://www.bautforum.com/space-astronomy-questions-answers/87199-there-way-humans-prevent-our-sun-becoming-red-giant.html

Grant, a bit off topic, but have you read Beech's terraforming book? I've been tempted to get it, but I haven't seen much in the way of reviews, and wouldn't want to bother with it if it mostly covers the same ground as Fogg or others.

grant hutchison
2010-Feb-06, 01:25 PM
Grant, a bit off topic, but have you read Beech's terraforming book?I haven't, sorry. Same reservations as you.

Grant Hutchison

novaderrik
2010-Feb-07, 08:56 AM
if you have that kind of technology, wouldn't it be easier to just find a new star to place your home planet in orbit around?

neilzero
2010-Feb-07, 01:03 PM
I just read the podcast of Frasier and Pamela and it agrees closely with the account by EDG. I'll try some numbers: The mass has stabilized at 1.02 solar mass, shortly before deuterium (= heavy hydrogen, with both a proton and a neutron) fusion begins. The protostar is about as hot as a main sequence type F star due to gravitational contraction. The powerful solar wind represents about the same mass as the mater falling in, so the star will never be this massive again. The deuterium fuses, then the lithium, keeping the photosphere at about type F star temperature. The core starts to contract and cool, but there is a delay of thousands of years (except for the loss of neutrinos) before the photosphere starts to cool, so the total mass is decreasing due to the strong solar wind. In a few? hours main sequence begins weakly, so the neutrinos resume, not many the first few centuries, until about the time the new energy source stops the contraction of the core. The photosphere continues to cool and reaches the lowest temperature = 5000 degrees k then very slowly warms over the next ten million years. The photosphere warms because the core helium is increasing as hydrogen fuses to helium. Apparently a tiny amount of hydrogen leaks into the core, otherwise the mass of the core would decrease as mass was converted to energy. If the mass of the core decreases the core can't get bigger except by getting hotter. If the core does not get bigger the the volume in which fusion occurs decreases, as the fusion migrates to the outer surface of the core. Are my details or logic in error? Perhaps the sun is not getting hotter, nor bigger at present? Neil

eburacum45
2010-Feb-07, 03:52 PM
if you have that kind of technology, wouldn't it be easier to just find a new star to place your home planet in orbit around?

Good strategy. The best stars to choose would be red dwarfs, as they will never go red giant, but will continue to shine get slightly hotter for a trillion years in some cases.

But the brighest stars today will go red giant (and some of them will explode). These are the stars giving off the most energy at the moment; it should be possible to use some of that energy to keep them shining for a while longer.

IsaacKuo
2010-Feb-08, 05:10 PM
Even without interstellar capability, moving a planet's population would require much less energy and effort than modifying the star. You just need to move outward enough to avoid being engulfed by the star, and use a giant sunshade to reduce the sunlight to the desired level.

Then, after the star shrinks into a white dwarf, you either move inward or you build a solar powered laser system to beam energy from the white dwarf to your habitats.

A white dwarf should be good for trillions of years...long enough that there's no compelling rush to move to a red dwarf system any time soon.

eburacum45
2010-Feb-08, 05:30 PM
The process of turning into a white dwarf is not exactly incident free;
see this timeline
http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html
there are flashes and pulses of energy and mass ejection described on that page which might inconvenience a population attempting to live there during that period. It might be nice to avoid as much of these events as possible, by starlifting if necessary.

astromark
2010-Feb-08, 06:40 PM
I have been watching and reading this thread with some considerable amusement...:)
Not like its ever possible to meddle with the processes of a stars evolution. Its not.
From where might a mass sufficant be found to prolong a stars lifespan ?
I might not be the brightest candle here but, even I understand the Mass requirement is just not available...
To the OP the only answer must surly be to build that Ark Ship and move away....
I understand that the measure of advancement of a race might include the control of their environment. But controlling a stars lifespan... NO.
Schoolboy fiction at best, sorry.

grant hutchison
2010-Feb-08, 06:53 PM
Schoolboy fiction at best, sorry.Martin Beech, who wrote the book about stellar rejuvenation which I referenced earlier, is a Professor of Astronomy in Regina, Canada.
So it might be more accurate (and significantly less patronizing) to use the phrase "academic speculation" instead of "schoolboy fiction".

Grant Hutchison

grant hutchison
2010-Feb-08, 07:16 PM
Thanks for the reference. That looks like an interesting book. At $5.92, including shipping, it is pretty reasonable.Sorry, I seem to have missed this earlier.
I'm glad it's of interest. :)

Grant Hutchison

IsaacKuo
2010-Feb-08, 07:58 PM
The process of turning into a white dwarf is not exactly incident free;
see this timeline
http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html
there are flashes and pulses of energy and mass ejection described on that page which might inconvenience a population attempting to live there during that period. It might be nice to avoid as much of these events as possible, by starlifting if necessary.
As long as there isn't anything like a supernova's neutrino pulse, hiding behind a sunshield should be less expensive and easier than the alternatives of moving to another star system or modifying the star.

(If there is a supernova neutrino pulse, then your best option is to move to another star system. No sunshield is thick enough in that case.)