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Lone Stars
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| Tank7 | Date: Saturday, 26.01.2013, 19:20 | Message # 1 |
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| In Space Engine 0.96, I found this star with no planets, no asteroids, nothing: RS 8403-196-8-1206772-149
I am wondering how common or rare this is expected to be. I know exoplanet detection is still too early to answer some of these questions with certainty, but I would love to hear your thoughts. Relevant to this is the Brown Dwarf Prevalence thread and the slight tangent it went into with even smaller physical bodies in the interstellar regions. I think I would expect at least some asteroids as an absolute minimum, unless heavier elements like carbon have not had time to form yet - perhaps a very very young star, the ultra hot blue ones, etc. So then it is all diffuse hydrogen gas outside the star which is quickly blown away by the solar wind as the star develops from it's infancy.
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| Tim | Date: Saturday, 26.01.2013, 23:40 | Message # 2 |
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| It's rare in SE, yet I've encountered many lone stars during my explorations. SE is probably even very optimistic on the percentage of stars that have planets. Alas I think so.
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| HarbingerDawn | Date: Saturday, 26.01.2013, 23:54 | Message # 3 |
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| Quote (Tim) I've encountered many lone stars during my explorations
I've never seen one. I had thought it was impossible.
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| Voekoevaka | Date: Sunday, 27.01.2013, 00:21 | Message # 4 |
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| In my case, I have seen one.
But I think it is impossible in real space. There is surely more than 1 billion objects around our sun, so this must be equivalent on others stars. We don't know any phenomenon that could detach all the objects of one star.
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| HarbingerDawn | Date: Sunday, 27.01.2013, 00:40 | Message # 5 |
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| Quote (Voekoevaka) We don't know any phenomenon that could detach all the objects of one star.
But it is not impossible that a star might form with no companions to start with. It would just likely be very rare. Also, if a star is part of a binary or multiple system and is ejected, then it would probably take nothing with it.
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| Tim | Date: Sunday, 27.01.2013, 13:53 | Message # 6 |
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| Btw, didn't the 1st generation stars have no planets?
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| HarbingerDawn | Date: Sunday, 27.01.2013, 14:37 | Message # 7 |
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| Quote (Tim) Btw, didn't the 1st generation stars have no planets?
Most likely. There were no heavy elements from which planets could form, and the environment was such that collapsing gas clouds tended to form stars, and very large ones.
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| Watsisname | Date: Sunday, 27.01.2013, 18:49 | Message # 8 |
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| In the current era, planet formation appears to be a natural part of star formation -- one can think of it as a way for collapsing molecular clouds to shed excess angular momentum.
Terrestrial planets definitely could not form around 1st generation stars, but gas giants may have been able to form. There's some debate still about the formation mechanism of gas giants -- do they start out the same way as terrestrial planets and then become massive enough to pull H/He out of the solar nebula? Or do they collapse directly out of the nebula due to a gravitational instability? Perhaps both? If the latter process happens, then it is possible that first generation stars could have had gas giants made purely of primordial elements.
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| Destructor1701 | Date: Sunday, 27.01.2013, 21:30 | Message # 9 |
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| Well, since stars form in the same basic manner as planets - a conglomeration of passing matter that becomes gravitationally bound, attracting more matter, and more, it would seem only natural that rather ephemeral gas giants probably did exist in the early days.
After all, if gas giants couldn't exist, then what were those stars, in their youth, prior to fusion initiating in their cores?
I could imagine primordial stars surrounded by a clutch of very light still-born brown dwarves and gas super-giants... I imagine anything smaller, made of light elements, wouldn't cling sufficiently against the prevailing gravity of the rest of the system's interactions.
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| apenpaap | Date: Sunday, 27.01.2013, 22:02 | Message # 10 |
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| I suppose it would be possible for a gas giant to form basically through a binary star forming process in which one star ended up extremely light (<~13 Jupiter masses), yeah. I wonder if a coreless gas giant like that would look very different from one with a rock and ice core like normal gas giants...
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| HarbingerDawn | Date: Sunday, 27.01.2013, 22:53 | Message # 11 |
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| Quote (Watsisname) Terrestrial planets definitely could not form around 1st generation stars, but gas giants may have been able to form.
I read something relatively recently that expressed the (surprising) fact that relatively metal poor stars actually had a lower occurrence of gas giants relative to terrestrial planets, indicating that at least some heavy elements are crucial to forming giant planets. I probably posted it on the forum somewhere, but I'm too lazy to hunt for it right now 
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| Watsisname | Date: Monday, 28.01.2013, 04:05 | Message # 12 |
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| That is surprising. I'll see if I can find some info on that when I have the time.
This is slightly tangential, but another compelling possibility regarding stellar metallicity and planet formation is that stars become more metal rich than they would otherwise be because planets migrate into them during the formation process and 'pollute' their atmospheres. The orbital decay time due to gas pressure of a forming planet is calculated to be so rapid that many planets might form and subsequently be destroyed in the star before the system reaches its 'final' state as the nebula is dispersed.
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| Tank7 | Date: Monday, 28.01.2013, 19:53 | Message # 13 |
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| Quote (Destructor1701) After all, if gas giants couldn't exist, then what were those stars, in their youth, prior to fusion initiating in their cores?
I like this logic  However, there is Harbinger's issue:
Quote (HarbingerDawn) I read something relatively recently that expressed the (surprising) fact that relatively metal poor stars actually had a lower occurrence of gas giants relative to terrestrial planets, indicating that at least some heavy elements are crucial to forming giant planets. I probably posted it on the forum somewhere, but I'm too lazy to hunt for it right now
I wonder if perhaps the once the star was born, the solar wind would disperse these primordial balls of hydrogen (perhaps slowly) without any reasonably dense core. So sure, there would be these early gas giants around 1st generation stars, at least at the time of star birth and solar system formation, but they wouldn't stay intact over cosmic timescales. This way we kind of have the best of both worlds to make the competing observations and theories work.
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| Watsisname | Date: Monday, 28.01.2013, 23:47 | Message # 14 |
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| Quote (Tank7) I wonder if perhaps the once the star was born, the solar wind would disperse these primordial balls of hydrogen (perhaps slowly) without any reasonably dense core.
Probably not; the solar wind even during the T-Tauri phase of a young star's life is mainly relevant to unaccreted gas and dust. A planet, even without the solid core, is much more robust and isn't affected much.
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