Can our sun last forever - especially as the Jeans mass lowers

newtonian · Sep 22, 2004

As per Biblical astronomy statements not yet on my list. The standard model has our sun burning out gradually after red giant stage. However, there is evidence of fine tuning. Scientific American some time ago ran an article concerning how a main sequence star can be rejuvenated upon collision with a brown dwarf. Meanwhile, as our main sequence sun gets older, the Jeans mass of the universe is also lowering. This is the critical mass necessary for coalescing of stars from star forming regions. See the December 2001 Scientific American concerning our universes oldest stars (not yet observed, btw). Am I correct in modeling the future universe as forming a higher proportion of brown dwarfs compared with main sequence today? In that case, what will the probability be that our sun will be rejuvenated in the future by collision with a brown dwarf - i.e. how much fine tuning would be required for this outcome? Or is it likely that our sun will have such a collision in the upcoming Andromeda merger? BTW- this is a spin-off from my old Andromeda collision thread which disappeared with the SDC crash.

Saiph · Sep 22, 2004

lets see: sun is 1 million miles across. Distance to nearest star is 24 trillion miles. Even if we absorb adromeda completely, thats only a doubling of stellar density. Heck, I'll give you triple, or 8 trillion miles. 8x10^12 / 1x10^6 = 8x10^6 Okay, thats a 1 in 8 million, all else being equal. Except...how long does each trail last? I.e. how long between attempt 1 and 2. About a million years, at least. So thats....one hit in 8x10^12 years. I don't see that happening. even at 100,000 years between attempts thats 8x10^11 years. Edited: I said 24 trillion ly instead of miles...my bad. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Maddad · Sep 22, 2004

Hmmm. 24 trillion miles to the neares star. 24 trillion light years would make for an lonely universe. This rejuvenation will happen for perhaps a single star during the galactic collision. It will not happen for great numbers of them, and it will not happen for one star several times over. The problem with rejuvenation is that the terrestrial planets themselves, such as Earth, will be gone by then. Even if Earth survives and remains orbiting the Sun, a brown dwarf would only add 1% or even less to the total mass, and thereby fuel supply, of the Sun. Since the Sun will be consuming fuel at up to 2,000 times faster then than it is now, that brown dwarf will add as little as 50,000 years to the lifespan of the Sun. For a star that will fuse hydrogen and then helium for 12,000,000 years before becoming a white dwarf, 50,000 years is not significant. Even though we have only a one in a hundred billion chance of being the lone star that collides with a brown dwarf, lets figure that we roll these long odds a second time and come up sevens again. The next rejuvenation lasts an even shorter period than the first one because the Sun is now more massive and therefore burns it fuel faster.

thalion · Sep 22, 2004

^ If the mass of the brown dwarf were simply added to the Sun, your scenario would be correct. However, at least in a collision between similarly-sized stars, at low speed, the collision would mix-up the stellar interior, basically spreading out the helium "ash" in its center with the star's bulk composition, and thus increasing the percentage of hydrogen in its core, and thus "resetting" its clock. This is probably exactly what has happened to "blue stragglers" in globular clusters. The price, as you mentioned though, is that the star is more massive, and thus has a shorter lifetime. However, a collision with a brown dwarf at say, the solar escape velocity would probably seriously damage or damage or destroy the Sun; being much denser, it would plow through the Sun like a bullet. There was a recent Sci. Am. article on stellar collisions recently listing the possibilities of various stellar collision scenarios; stay tuned.

Maddad · Sep 22, 2004

Thalion However you slice it, if yo want the sun to last longer then you have to provide it with more fuel. Brown dwarfs are about 1% the mass of the sun, so they won't help much, regardless of mixing. You cannot burn what isn't there.

Saiph · Sep 22, 2004

hmmm....I don't think the brown dwarfs are more dense. They weigh less, and are under the same hydrostatic conditions as a star. Sure, the star has a lot of outporing energy, that helps reduce density while maintaining pressure. However, it's also a LOT bigger. Hmmm....i'd have to run some numbers. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Sep 22, 2004

Oh, and mixing is a very important aspect of stellar life-cycles. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

thalion · Sep 23, 2004

I'm pretty sure they're significantly more dense. The Sun's average density is 1.4 g/cm^3. Let's take a brown dwarf with roughly 6% of the Sun's mass, but 1/10th of its diameter. With roughly 1/1000th the Sun's volume but 6/100ths of its mass, its density would be roughly 60 times greater than the Sun's, some 84 g/cm^3. At least, that's what my numbers are telling me; feel free to double check or critique them.

Saiph · Sep 23, 2004

density, however, is much greater near the core where it counts in this case. But yeah, the suns energy output bloats the volume, and drops the density. So you may be right. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Sep 24, 2004

Thalion -Thank you. I didn't know about blue stragglers. I do not believe the result would be a more massive sun in the long run, since the sun is losing mass in the meantime - correct? How long would it take our sun to lose a mass equivalent to a brown dwarfs mass? Yes, I had that very interesting article at sciam.com in mind.

newtonian · Sep 24, 2004

Saiph - Thank you. You are calculating based on density. It is not that simple. Gravitational attraction will bend to trajectories of both masses as they near, so that near misses are less likely than by mere density. Relative speed (velocity?) will determine how much the respective trajectories will be effected by gravity. I know it would require fine tuning, or be unlikely. Many factors which allow our universe to allow stars and life, plus many factors which allow our earth (plus the sun, Jupiter, etc.) to sustain life, are unlikely. Which is more unlikely, however? To go in depth on fine tuning should be another thread. Suffice it to say here that the expansion rate, which is much more complex than thought just 20 years ago, is fine tuned very precisely. A little slower (at the big bang) and our universe would have collapsed by now; a little faster (at the big bang) and the universe would have dissipated by now. Ditto the exact proportions (e.g. ratios of strengths) of the 4 forces of physics and the triple matching of the nuclear resonances of Helium, Berrlyium and carbon in stars which allows carbon synthesis.

newtonian · Sep 24, 2004

crazyeddie - Oops, my response to you on fine tuning was posted accidentally in response to Saiph - please see above.

newtonian · Sep 24, 2004

You all - don't forget the lowering of Jean's Mass. See Scientific American, December 2001, article entitled ?The First Stars in the Universe.? The Jean's mass at the time of the earliest stars was much greater than today. The Jean's mass is the critical mass that will allow gravitational collapse (i.e. accretion in a star forming gas cloud). It is therefore deduced that the earliest stars were much more massive than our sun. BTW- they also would contain less or no 'metals' (astronomy definition: elements other than Hydrogen, Helium, lithium - different from the definition in chemistry) since no stars had yet synthesized additional elements to the Hydrogen, Helium and Lithium synthesized in the big bang. Wouldn't the lowering of Jean's Mass due to lowering of density caused an increased proportion of brown dwarfs? Could there be more brown dwarfs than we suspect, masking as dark matter?

Saiph · Sep 24, 2004

<blockquote>In reply to:<hr />Gravitational attraction will bend to trajectories of both masses as they near...<hr /></blockquote> That would be gravitational cross section. Which I don't want to calculate right now. However, it usually only adds an order of magnitude to such calculations. As for which is likely, a brown dwarf in a pre-ordained collision with the sun billions of years after formation (in a naturally chaotic universe) or the fine tuned constants that allow life (as we know it) to exist.... That's the anthropic principle, which I don't get into for obvious reasons. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Sep 25, 2004

Saiph - Well, I prefer to avoid the anthropic priniciple also, since it is essentially philosophy which is based on speculations rather than observations. However, the specifics such as the exact triple matching of the nuclear resonances of Helium, Berylliuim and carbon for carbon synthesis in stars involve real observational science, not mere philosophy. Granted, there are often disagreements when probability and statistics is applied to the actual observations. Nevertheless, probability and statistics is also a real science, not mere philosophy. Other posters have already given real math estimates for a brown dwarf collision. How does this translate into a probability - I'm looking for ball park estimates - a few powers of 10 off are OK for my question? And, am I correct in reasoning that lower mass stars, like brown dwarfs, become more probable as the Jean's mass lowers due to lowering average density as our universe expands?

Saiph · Sep 26, 2004

Scientific base or not for the speculation, probability doesn't matter after the fact. No matter how unlikely to occur, once it does happen, it's there to stay. Basically things are the way the are now, because of the various values for the constants. So things work a certain way. If those values were different, things would work differently. And if life can arise in those situations, they'd be just as valid to say, "gee, look at how its set up, it so perfect to explain how things work!". Basically, of course a certain cause (various constant values) gives us a certain effect (what we see today). Personally, if the constants came out in a way that couldn't be reconciled with what we saw...then I'd be worried. Anyway, what matters most in stellar formation is consistency. Not only do y ou need enough mass, you need it clumped within a certain volume. And that volume depends on the average density of the medium around it (need a bigger mass and/or smaller volume in a dense cloud vs a sparse cloud) IIRC. So I don't know. It may work that way. But even if it does result in a greater percentage of formed stars being brown dwarfs, the total number of stars will likely decrease. So your brown dwarf creation rate's may actually decline, despite thier prefered production status. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Sep 27, 2004

Saiph- well, the argument that we are here because if our universe wasn't this way we wouldn't be here - or some facsimile of those words- does not make sense to me as an example of cause and effect. And, please understand, I do not claim to know the truth on the theme of this thread. It is a question. That being said, the average Jean's mass of our universe has lowered since our sun was formed - so my question should translate into actual observations of the contents of our universe in the last 5 or 6 billion years - assuming our estimate of our sun's age is in the ballpark. So, do we see an increase in brown dwarf proportions in the last few or several billion years? Take note that brown dwarfs can be invisible from our distance, so we may percieve them as dark matter.

newtonian · Oct 1, 2004

eburacum45 - muons? Later on that. On your earlier post: Yes, I know that the bigger, or more specifically more massive, the star the shorter its life span - all other factors being equal. However, two factors you seem to be ignoring in that generalization: 1. Internal mixing - you are assuming internal mixing is equal in all stars, that no stars have internal magnetic fields that cause additional mixing which effects their life span. I do not accept that assumption as being accurate. 2. Mass loss in time - You are ignoring the loss of mass of a star as it burns its fuel. Its mass does NOT stay the same. You all - so is the proportion of brown dwarf production vs. main sequence star production increasing with time as the average Jean's mass lowers with the lowering average density of our universe? Or, has the brown dwarf density already increased, so that a high proportion of dark matter in our galaxy at present is brown dwarfs?

newtonian · Oct 2, 2004

stevehw33 - Interesting alternative fuel. However, the muon has a very brief lifespan before decaying: 2.197x10^-6 seconds (a little more than a millionth of a second). So I also ask: where would the muons come from - what would be the postulated sequence or steps? BTW, the muon is negative and decays to an electron, a muon-neutrino and an electron anti-neutrino. Have we detected electron anti-neutrinos coming from our sun? My understanding is that muon neutrinos would morph along with tau neutrinos and electron neutrinos- correct? Or is that just theory to account for the lower number of neutrinos than expected that have been observed coming from our sun?

nexium · Nov 1, 2004

Did you conclude the average speed difference would be 8 trillion divided by one million = 8 million miles per year = 22,000 miles per day = 900 MPH? At ten times that fast, does not the probability increase by ten times? Did you neglect to consider that stars in both galaxies are orbiting quite fast at approximately right angles to the merging of the galaxies direction? Also when the stars are approching each other almost head on, a billion miles apart, is there not a significant turning toward each other (due to gravity) perhaps doubling the probability of impact? Where very near misses occur, both stars will change direction radically and one will increase speed due to gravity assist manuever. Could this possibly double the frequency of future collissions? Is it possible that the average spacing of brown dwarfs in both galaxies is 12 trillion miles, increasing the collision probability by 8 times? That would mean 1600 billion brown dwarfs in our galaxy, compaired to 200 billion main sequence stars, at present. A collision or even a very near miss with a compact star could mean scattered mass from our sun reducing it from G2 to a type k star with longer life. Please correct my logic and arithmetic, as I likely made at least one error. Even if all these apply, plus mixing refuels for 200,000 years instead of the theorized average refueling for 50,000 years, it seems very unlikely that Sol will stay on main sequence for more than an extra billion years, unless God is making sure our sun gets extra collisions. Neil

nexium · Nov 1, 2004

Jupiter has about double the average density of the three smaller gas giants, so the average density of a brown dwarf may be several times the average density of our Sun. Even if so, my gusss is little dwarf (class M star collisions with our sun may be much the same as brown dwarfs) material would get past the center of the sun's core (very high density) unless it was a glancing blow, or the impact speed exceeded a million miles per hour (very unlikely) Compact stars are all but sure to pass all the way though and scatter a signicant percentages of the sun's mass into space. Five billion years from now, is it reasonable to assume there will be ten times as many compact stars as mainsequence stars in both galaxies? Essentually all of the OBA and F stars born in 15 billion years will be cold compact stars by then, unless they are reheated temporarily by infalling matter, or numerious new OBA and F stars are formed because of passing though Andromeda. Neil

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