John Dobson's View on Defining Gas Giants as Stars or Planets.

[renormalised (Carl)]

The only surefire way of checking the metal content of the crust of any planet is to go there and take samples. Once again, this is a case of trying to extrapolate from one example. However, given that the other terrestrial planets also underwent the same bombardment as the Earth did, it would be not unreasonable to assume that they also gathered up more precious minerals and metals than they would've otherwise had in their crusts and mantles. After that, the mineral distribution would depend on the geological processes that occurred on those planets.

Nothing unusual about meteorites bringing in extra materials and giving the planet more precious metals in its crust and mantle than would otherwise be there.

In any case, planets aren't categorised on the basis of metals content, unlike stars. Most stars are not all that hard to categorised on the basis of metals content, either. The star in question is just one of a number of extreme cases which are hard to reconcile with current stellar evolutionary theory....but not impossible.

[CraigS]

Originally Posted by renormalised

However, given that the other terrestrial planets also underwent the same bombardment as the Earth did, it would be not unreasonable to assume that they also gathered up more precious minerals and metals than they would've otherwise had in their crusts and mantles. After that, the mineral distribution would depend on the geological processes that occurred on those planets.

Nothing unusual about meteorites bringing in extra materials and giving the planet more precious metals in its crust and mantle than would otherwise be there.

Yep .. so within banded regions, one would expect the proportions of their fundamental compositions, as far as metallicity is concerned, to be similar.

Originally Posted by renormalised

In any case, planets aren't categorised on the basis of metals content, unlike stars.

Perhaps not yet, (due to lack of real data/evidence), however the proportions and states of the metallic elements which make up the layers of planets (and moons) is clearly important .. and very much effects large-scale surface conditions and atmospheric environments.
I notice that current evidence-based hypotheses, for the elemental metal makeup of the Solar System planets and moons (within similar regions), already varies quite significantly … even amongst those which received the same bombardments.

This would have to change, as they gather more data and move away from our present earth-centric view of planetary evolution.

Cheers

[shelltree (Shelley)]

Originally Posted by renormalised

The problem with that star, Suzy, is that it has such a low metals content that it's hard to see how such a star could've formed in the first place. Without going into the particulars of the mechanisms by which a gas cloud collapses to form a star, the dearth of metals within the cloud that formed this star would've normally made it very difficult for the cloud to collapse to form the star/stars in the first place....especially low mass stars like this one. With clouds that have such a low metals content, the clouds have a hard time trying to collapse because of the internal pressures generated by heating within the cloud. The presence of metals actually allows the cloud to radiate away that heat more efficiently than it would otherwise. The only way for metal deficient clouds to collapse is to build up mass, to a point that the instabilities within such clouds allows the gravity to collapse the clouds and form stars...which are usually much larger than they would normally otherwise be. That's why the early PopIII stars were so large because they formed from clouds of almost pure hydrogen and helium. Instead of many smaller stars forming from the clouds, the clouds collapsed and formed one or two very large stars...some of which may have weighed as much as 1000-2000 solar masses, possibly even more. Not only that, but nearly all of those stars were much hotter than today's stars. Because a cloud of almost pure hydrogen and helium is relatively transparent to radiation, in order for a star to be of a certain spectral class, it has to be hotter than it would be if it was like stars of today. Some of these giants in the beginning radiated at temps of around 250000-500000K and the largest of them were more than 1 billion times brighter than the Sun. They would've lasted only a few hundred thousand to a millions years or two before they all went hypernova and/or collapsed into black holes. The star they were talking about in the article isn't a PopIII star, despite its low metals content and age. It's more like what they call an extreme PopII star, much like the halo stars surrounding our galaxy, only with even less metals than what most of them have. It's more than likely one of the first stars that formed in the generation immediately proceeding the PopIII era, or very close to that time. There's bound to be more of these types of stars populating the halo and spread amongst the stars of the spiral. It's just a matter of time before than find them.

What is "PopIII" and "PopII" referring to?

And are you saying it is possible for this SDSS J102915+172927 star to have formed in the same way that you have explained above? Through a gas cloud of hydrogen and helium that becomes so large that its gravity finally forces it to collapse to form the star? And yet it is estimated to be around 13 billion years old! Could this type of star that is deficient of metals continue to "live" so long and if so, how would it be possible?

I find this all very interesting and if I have for any reason misunderstood anything please forgive me, I'm just trying to wrap my head around it all!

Fascinating stuff I must say

[Suzy]

Shelley is learning about stars as well and we often facebook each other trying to learn astro things. So you have two very eager students here desperate for knowledge on all things (confusing ) stars. We also have to be careful on facebook that we get our genetives correct when we talk about constellations because Les doesn't like that. Sometimes he issues us a quizz (hard ones ) which i fail at because Shell goes off googling and I use up the time looking through my books or pondering my brain, so one guess who wins by getting the answers first.

To Shelley:


Okay, so back on topic...

Wow, i did not know about how a star gets Lithium.. fascinating!
I wish i paid more attention in science class in school.
With what you said about stars showing an abundance of lithium when they consume a planet... do they already have some amount of lithium present before a planet consumption?

Carl, thanks heaps for going into great detail to explain things. I'm going to copy/paste the information you gave and pop it into my "stars" file so I can keep learning.
Fascinating stuff.

Craig, as usual, I always look to your input as well, many thanks also.

Les, that was one story and a half- thanks so much for sharing it.
He gave Mike Simmonds a bit of a run a few times in that interview as well. Though he did answer the question for Mike- re what he likes to look at, with the answer being galaxies.
Yes, I guess I found him engaging- you said it well in a nutshell. However, I haven't met him nor seen much footage on him but from what I've come to understand so far, he seems to have a reputation for being quite abrasive (for want of a better word?). Did you'll notice right at the end of the interview when the time was up, he wanted to talk about cosmology but ... "cut". It was almost as if Mike had said to him we are not going to talk about cosmology during the interview and as soon as it finished, Dobson tried to bring it up..."That's for another time.." I think were the last words.

[renormalised (Carl)]

Originally Posted by shelltree

What is "PopIII" and "PopII" referring to?

And are you saying it is possible for this SDSS J102915+172927 star to have formed in the same way that you have explained above? Through a gas cloud of hydrogen and helium that becomes so large that its gravity finally forces it to collapse to form the star? And yet it is estimated to be around 13 billion years old! Could this type of star that is deficient of metals continue to "live" so long and if so, how would it be possible?

I find this all very interesting and if I have for any reason misunderstood anything please forgive me, I'm just trying to wrap my head around it all!

Fascinating stuff I must say

PopIII and PopII are designations for stars of a certain type that depend on their metals content and orbital dynamics about the centre of the galaxy (any galaxy, actually). Once a star's metals content drops below a certain percentage relative to the Fe/H ratio of the Sun, it's given the designation PopII or PopIII. Most PopII stars have low to extremely low metals content (10%< relative to the Sun) and PopIII stars, the hypothetical stars that formed only a few hundred million years after the BB, have no metals at all, except for a tiny amount of Lithium (and possibly Beryllium) that formed during the BB.

Most PopII stars either reside in the galactic bulge of galaxies or in their halos. They were amongst the first stars to form within the galaxies.

All stars, whether they're SDSS J102915+172927, a PopIII object or the normal run of the mill ones we see today all form in the same way...the collapse of a cloud of hydrogen and helium. It's just that later generations of stars after the PopIII stars burnt out contain more heavy elements in their makeup than the original stars. All due to those stars and other spewing those elements out into the cosmos after they die. The previous generations of stars made the elements out of which the new generations were born from.

The mechanisms by which a gas/dust cloud collapses to form a star are a little more complicated than just gravity collapsing the cloud, but once it starts to collapse gravity becomes the dominant force.

The lifetime of a star is directly proportional to the inverse 2.5 power of the mass of the star....This value is multiplied by 10^10, or the average MS lifetime of a star like the Sun, to give the star's MS lifetime. The star in question is 0.8 solar masses, which is why it can last for 13 billion year or more, because its MS lifetime is (1/0.8^2.5) x 10^10 or 17.5 billion years. However, for very high mass and low mass stars, the relationship of mass to lifetime is a little more complicated and the exponent of the mass is slightly different. Though, the above example will generally give good approximate ages for stars between 0.1 to 40 solar masses.

[renormalised (Carl)]

Originally Posted by Suzy

Wow, i did not know about how a star gets Lithium.. fascinating!
I wish i paid more attention in science class in school.
With what you said about stars showing an abundance of lithium when they consume a planet... do they already have some amount of lithium present before a planet consumption?

Carl, thanks heaps for going into great detail to explain things. I'm going to copy/paste the information you gave and pop it into my "stars" file so I can keep learning.

Fascinating stuff.

Lithium starts to fuse at around 4-5 million K and what little lithium that maybe present in the upper layers of a star is usually convected down into the hotter layers rather quickly and then it sinks to where it begins to fuse into heavier elements....namely beryllium and boron (neither of which last much longer, either). If a MS star shows an abundance of lithium in its spectrum it usually means either of two things.....it has swallowed a giant planet or planets, or it's very young. With most MS stars with planets, they've exhausted their supplies of lithium well before any planets become engulfed by the star. It usually disappears within a few million years or less.

Good to see my pontifications have some value

[shelltree (Shelley)]

Originally Posted by Suzy

Shelley is learning about stars as well and we often facebook each other trying to learn astro things. So you have two very eager students here desperate for knowledge on all things (confusing ) stars. We also have to be careful on facebook that we get our genetives correct when we talk about constellations because Les doesn't like that. Sometimes he issues us a quizz (hard ones ) which i fail at because Shell goes off googling and I use up the time looking through my books or pondering my brain, so one guess who wins by getting the answers first.

To Shelley:

I had a hard enough time getting to sleep on Friday night because I couldn't stop thinking about Wolf Rayet stars and their temperatures and their violent conditions and...and...and...phewf! But I am very, very intrigued to learn as much as possible about stars, how they are born, how they live and die, everything! It can be so confusing though...

And in my defence Suz, I went away and went through goodness knows how many constellations on wiki to figure it out without google's trusty assistance But no, it was utterly baffling! I will forever remember now that Alpha Muscae is the lowest mag "alpha" star in any constellation The genetive is right and everything (Hi Les )

Originally Posted by renormalised

PopIII and PopII are designations for stars of a certain type that depend on their metals content and orbital dynamics about the centre of the galaxy (any galaxy, actually). Once a star's metals content drops below a certain percentage relative to the Fe/H ratio of the Sun, it's given the designation PopII or PopIII. Most PopII stars have low to extremely low metals content (10%< relative to the Sun) and PopIII stars, the hypothetical stars that formed only a few hundred million years after the BB, have no metals at all, except for a tiny amount of Lithium (and possibly Beryllium) that formed during the BB.

Most PopII stars either reside in the galactic bulge of galaxies or in their halos. They were amongst the first stars to form within the galaxies.

All stars, whether they're SDSS J102915+172927, a PopIII object or the normal run of the mill ones we see today all form in the same way...the collapse of a cloud of hydrogen and helium. It's just that later generations of stars after the PopIII stars burnt out contain more heavy elements in their makeup than the original stars. All due to those stars and other spewing those elements out into the cosmos after they die. The previous generations of stars made the elements out of which the new generations were born from.

The mechanisms by which a gas/dust cloud collapses to form a star are a little more complicated than just gravity collapsing the cloud, but once it starts to collapse gravity becomes the dominant force.

The lifetime of a star is directly proportional to the inverse 2.5 power of the mass of the star....This value is multiplied by 10^10, or the average MS lifetime of a star like the Sun, to give the star's MS lifetime. The star in question is 0.8 solar masses, which is why it can last for 13 billion year or more, because its MS lifetime is (1/0.8^2.5) x 10^10 or 17.5 billion years. However, for very high mass and low mass stars, the relationship of mass to lifetime is a little more complicated and the exponent of the mass is slightly different. Though, the above example will generally give good approximate ages for stars between 0.1 to 40 solar masses.

This makes a lot more sense! Even after I wrote my response, I had a feeling I hadn't really thought about it hard enough or read enough But this clears it up for me perfectly, thanks Carl And that is one doozy of an equation... (well, for me anyway ) but generally what it represents makes sense...although what does MS stand for? I just spent the past 15 minutes trying to figure out that equation on my calculator... and I got 17469281074.217107003196669286963 LOL.

Not sure why I even bothered trying

[OICURMT]

Originally Posted by Suzy

http://www.youtube.com/watch?v=NnIf2...eature=related

Definitely fast forward... you will thank yourself for doing so...

[renormalised (Carl)]

Shelley, MS = Main Sequence or your ordinary, core hydrogen fusing, stars.

A.K.A Luminosity Class V...which is where you get part of the notation for the written spectral classes of stars, e.g. our Sun is a G2V class star. A hypergiant is class 0, supergiant I, bright giant II, giant III, subgiant IV, sub dwarf VI and the white dwarfs are VII.

Then you have the HR diagram's MK (Morgan-Keenan) sequence...W, O, B, A, F, G, K, M, L, T and now a new class Y, for the dimmest and coolest brown dwarfs. You also have subclasses of stars that are generally lumped in with M....C (carbon stars, that are made up of old classes R and N) and S (shell stars, which can also be C class stars as well). Each spectral class is also divided into 10 subclasses, from 0-9...G0-G9, for example (they can also be divided up into 10 sub-subclasses as well, e.g. G2.5, B1.9 etc). Traditionally, the hottest of the O class stars was O3, but that maybe revised to account for some of the very hottest and largest of MS stars, like those recently found in R136a in the LMC.

Also, with W class stars (the Wolf Rayet's), you have classes WC and WN, depending on whether they exhibit abundant carbon or nitrogen in their spectra. All W class stars have hydrogen deficient spectra as they've basically blown off their outer layers and are essentially the exposed cores of the original stars.

[renormalised (Carl)]

Originally Posted by shelltree

I had a hard enough time getting to sleep on Friday night because I couldn't stop thinking about Wolf Rayet stars and their temperatures and their violent conditions and...and...and...phewf! But I am very, very intrigued to learn as much as possible about stars, how they are born, how they live and die, everything! It can be so confusing though...

And in my defence Suz, I went away and went through goodness knows how many constellations on wiki to figure it out without google's trusty assistance But no, it was utterly baffling! I will forever remember now that Alpha Muscae is the lowest mag "alpha" star in any constellation The genetive is right and everything (Hi Les )



This makes a lot more sense! Even after I wrote my response, I had a feeling I hadn't really thought about it hard enough or read enough But this clears it up for me perfectly, thanks Carl And that is one doozy of an equation... (well, for me anyway ) but generally what it represents makes sense...although what does MS stand for? I just spent the past 15 minutes trying to figure out that equation on my calculator... and I got 17469281074.217107003196669286963 LOL.

Not sure why I even bothered trying

Just remember either of these equations (whichever is easiest)....

(1/M^2.5) x 10^10, or, ((M/M*)^-2.5) x 10^10. M* is the mass of the sun, which is usually taken as having a value of just 1.

[shelltree (Shelley)]

Originally Posted by renormalised

Shelley, MS = Main Sequence or your ordinary, core hydrogen fusing, stars.

A.K.A Luminosity Class V...which is where you get part of the notation for the written spectral classes of stars, e.g. our Sun is a G2V class star. A hypergiant is class 0, supergiant I, bright giant II, giant III, subgiant IV, sub dwarf VI and the white dwarfs are VII.

Then you have the HR diagram's MK (Morgan-Keenan) sequence...W, O, B, A, F, G, K, M, L, T and now a new class Y, for the dimmest and coolest brown dwarfs. You also have subclasses of stars that are generally lumped in with M....C (carbon stars, that are made up of old classes R and N) and S (shell stars, which can also be C class stars as well). Each spectral class is also divided into 10 subclasses, from 0-9...G0-G9, for example (they can also be divided up into 10 sub-subclasses as well, e.g. G2.5, B1.9 etc). Traditionally, the hottest of the O class stars was O3, but that maybe revised to account for some of the very hottest and largest of MS stars, like those recently found in R136a in the LMC.

Also, with W class stars (the Wolf Rayet's), you have classes WC and WN, depending on whether they exhibit abundant carbon or nitrogen in their spectra. All W class stars have hydrogen deficient spectra as they've basically blown off their outer layers and are essentially the exposed cores of the original stars.

I have been learning the MK sequence and I have also included L, T, and new class Y as well in my learnings, it's very interesting. And did not realise there was also C class, as well as S class stars, I will have to look into it further and broaden my readings. I know there are a lot of different ways of classing stars but I'll learn them one at a time so as not to confuse myself too much And yes, I read about the WC and WN classes of W or WR stars but on wikipedia they also had WCE/WCL and WNE/WNL classes E representing "early" and L representing "late". Does that just mean that some are classes as W stars in the "early" stages and some in the "late" stages? Or early being still abundant with carbon or nitrogren and late, there being less noticeable traces in the spectra?

The fact that W class stars are hydrogen deficient is one of the things that has stuck with me since starting to learn more about them, having the hydrogen stripped from hot stellar winds. I thought that was really intriguing, what a violent place to be! They are also suppose to range from between 250000K and 300000K as well, aren't they? I read that somewhere in my readings as well but I cannot remember where.

Originally Posted by renormalised

Just remember either of these equations (whichever is easiest)....

(1/M^2.5) x 10^10, or, ((M/M*)^-2.5) x 10^10. M* is the mass of the sun, which is usually taken as having a value of just 1.

I tried the first equation and ended up again with the original gigantic number I had got. When I tried the second equation, my result was -17000000000 Err, LOL. Needless to say I have no idea what I'm doing. I tried using it on Alpha Centauri, which is 0.97 solar masses and I got two completely different results for both as well. The one that was the least ridiculous was -15300000000. Am I silly to think that means 15.3 billion years?

Anyway, please tell me sincerely if I should just leave the equations to the scientists and mathematicians I do find this all really interesting and want to learn as much as possible but I also don't want to bug you too much with my silly questions, Carl

Thanks for all of your help so far, you're a gem!

[Suzy]

Originally Posted by shelltree

And in my defence Suz, I went away and went through goodness knows how many constellations on wiki to figure it out without google's trusty assistance

Wiki/google, potato/patata, same thing

Originally Posted by shelltree

what does MS stand for?

Shell, if it helps you any, he had me miffed on that one too.

Sorry Carl, we're probably not making your job very easy , but where keen learners, yes, yes!

Carl, many thanks for your explanations regarding lithium- you've explained it beautifully with it being easy to understand. It's nice and clear to me now.
There is so much great info in here to go into my "star" folder for future reference.

@ OIC.

[Suzy]

You are a fantastic teacher, Carl.

[renormalised (Carl)]

Originally Posted by shelltree

I have been learning the MK sequence and I have also included L, T, and new class Y as well in my learnings, it's very interesting. And did not realise there was also C class, as well as S class stars, I will have to look into it further and broaden my readings. I know there are a lot of different ways of classing stars but I'll learn them one at a time so as not to confuse myself too much And yes, I read about the WC and WN classes of W or WR stars but on wikipedia they also had WCE/WCL and WNE/WNL classes E representing "early" and L representing "late". Does that just mean that some are classes as W stars in the "early" stages and some in the "late" stages? Or early being still abundant with carbon or nitrogren and late, there being less noticeable traces in the spectra?

The fact that W class stars are hydrogen deficient is one of the things that has stuck with me since starting to learn more about them, having the hydrogen stripped from hot stellar winds. I thought that was really intriguing, what a violent place to be! They are also suppose to range from between 250000K and 300000K as well, aren't they? I read that somewhere in my readings as well but I cannot remember where.

Here's a page that gives a good description and definition for WR stars...

https://www.cfa.harvard.edu/~pberlind/atlas/htmls/wrstars.html

The temps you quoted are too high for a WR star...more applicable to the newly exposed cores of red giants in the very earliest stages of PN's, called PN Variables. Chop a zero off the temp and you're closer to what WR stars radiate at.

Originally Posted by shelltree

I tried the first equation and ended up again with the original gigantic number I had got. When I tried the second equation, my result was -17000000000 Err, LOL. Needless to say I have no idea what I'm doing. I tried using it on Alpha Centauri, which is 0.97 solar masses and I got two completely different results for both as well. The one that was the least ridiculous was -15300000000. Am I silly to think that means 15.3 billion years?

Anyway, please tell me sincerely if I should just leave the equations to the scientists and mathematicians I do find this all really interesting and want to learn as much as possible but I also don't want to bug you too much with my silly questions, Carl

Thanks for all of your help so far, you're a gem!

You must've input the numbers wrong to get -ve answers. It's the exponent that's -ve, not the whole formula, which is the only way you'll get a -ve answer.

Actually, Alpha is 1.09 solar masses, so the answer is 8.06 billion years.

Hey, bug me with as many questions, silly or not, as you like. I'm more than happy to help out

[shelltree (Shelley)]

Turns out I just needed a better scientific calculator and Windows 7 calculator is pathetic

So, if we use the example of Alpha Centauri again, being 1.09 solar masses, then the equation would be the following? ((1.09/1)^-2.5)x10^10, which equates to 8,061,832,212.95

Is that correct? I haven't checked out the link for Wolf Rayet stars yet but I might start reading some of it now

[renormalised (Carl)]

Originally Posted by shelltree

Turns out I just needed a better scientific calculator and Windows 7 calculator is pathetic

So, if we use the example of Alpha Centauri again, being 1.09 solar masses, then the equation would be the following? ((1.09/1)^-2.5)x10^10, which equates to 8,061,832,212.95

Is that correct? I haven't checked out the link for Wolf Rayet stars yet but I might start reading some of it now

Yep, that's correct

There's a textbook you can buy, called "Stellar Spectral Classification" by Richard Gray and Christopher Corbally. It's very in depth and is for graduate students and lecturers, but it isn't too onerous that you wouldn't be able to follow much of what's written in the book. It's the recommended text for studying spectra, actually. If you want to get it, goto Fishpond.com.

[renormalised (Carl)]

Originally Posted by Suzy

You are a fantastic teacher, Carl.

Thank you

I really appreciate that

[PetarB (Petar)]

Really quite an interesting thread - and thanks Carl for your scholarly illustrations!

Shelley you should be aware that Window's calculator has been shown to be ocassionally flaky. Don't ask me how something as basic as a calculator app can return an incorrect result, but there's Microsoft for you! But it sounds like that wasn't the issue in your algebra in anycase...

As for as the definition of a planet goes, IMHO Jupiter and Saturn clearly do not qualify for even 'failed star' appellations.

However, I do imagine the sentinent denizens of exsolar gas-giants laughing amongst each other at the little 'rocks' in their own planetary systems.

"Should we name them planets? They seem rather small, barren and uninteresting by our standards!"

"Oh yes, they have no 'atmosphere' to speak of! There will be little possibility of life, or other points of interest in such tiny and rocky geospheres..."

[AstralTraveller (David)]

I concur with Ron and Les. He made some great innovations in the construction of telescopes but that is where his expertise ends. I was going to pull some of his 'theories' apart but after seeing how he dealt with any probing questions I decided it wasn't worth the grief. I had been forewarned, so his attitude that night wasn't an aberration.

[Suzy]

Originally Posted by AstralTraveller

I concur with Ron and Les. He made some great innovations in the construction of telescopes but that is where his expertise ends.

I'll say.

Originally Posted by AstralTraveller

I was going to pull some of his 'theories' apart but after seeing how he dealt with any probing questions I decided it wasn't worth the grief. I had been forewarned, so his attitude that night wasn't an aberration.

With respect Mr Dobson, if you don't hold a degree in this field, nor have enough weight to the theory to have it peer reviewed or whatever those people do to have a plausibility factor, I say keep your opinions to yourself and out of public broadcasting as people like me who are trying to learn get even more confused.
His view mucked me around no end hence the need to post this thread.

He is bare faced using his "fame" thru the media to get his own theories across, just plain wrong.
I'm extra cranky at the moment, I just want it to stop raining already. Dobson was the casualty.

Apologies if I sound a tad harsh (see, there's still niceness amongst the angst ).