Timeline for How can a gas giant be about the same size but six times more massive than Jupiter?
Current License: CC BY-SA 3.0
15 events
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| Mar 28, 2016 at 16:31 | comment | added | ProfRob | @Aron Kinetic energy $\neq$ heat in a degenerate object. The dividing line between degenerate brown dwarfs/planets and non-degenerate stars is precisely where objects contract and become sufficiently hot to initiate hydrogen fusion. Stars and brown dwarfs do not. | |
| Mar 28, 2016 at 15:52 | comment | added | Aron | @Joshua but how would such an object form without heating up? I mean all that mass must have kinetic energy equivalent to the binding energy of the body to begin with... | |
| Mar 28, 2016 at 14:47 | comment | added | NeutronStar | @Aron, to add to what Chris White said, it is worth mentioning that it is partially because of the relatively low central temperatures of these objects that degeneracy pressure is able to be dominant. If the temperatures were higher (I don't know specifically how much higher), then the pressure support would come from the thermal energy of the matter and the electron degeneracy would be lifted. | |
| Feb 17, 2015 at 8:22 | comment | added | ProfRob | @Steveverill Yes. Perhaps I should have added error bars... The low-mass objects will be predominantly Kepler transits and will often have large mass uncertainties. The hot Jupiters are much more precise. | |
| Feb 17, 2015 at 3:40 | comment | added | Level River St | The new graph looks great! That planet with 0.01 jupiter masses and density of nearly 10^6 kg/m3 looks odd though. I followed the link in the graph and it appears to be Kepler 37b with a density of "650+/-850g/cm3" in other words they're not really sure what the density or mass is I guess. I found it hard to understand how an object not much more massive than Earth with a density more than an order of magnitude higher than what we know from conventional chemistry could come to exist. | |
| Feb 16, 2015 at 19:40 | vote | accept | Quantum Force | ||
| Feb 16, 2015 at 11:45 | history | edited | ProfRob | CC BY-SA 3.0 |
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| Feb 16, 2015 at 11:40 | history | edited | ProfRob | CC BY-SA 3.0 |
added 723 characters in body
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| Feb 16, 2015 at 10:28 | comment | added | Level River St | @RobJeffries In that case that point at bottom left is a bit of an outlier. What you are saying is more in agreement with the black line. It's true that Saturn is about 1/3 the mass of Jupiter and 1/2 as dense. It would be nice to see a graph of density versus M if you had one. But then on the other side of the graph we see that for stars, radius depends almost linearly on M, so bigger stars are much less dense, presumably because of the higher temperature. An individual star's radius also varies a lot during its lifetime though, so I'm not 100% sure how to interpret that. | |
| Feb 16, 2015 at 10:03 | comment | added | ProfRob | @steveverrill Wishful thinking I'm afraid. Density goes roughly as $M$. Degeneracy is not the only thing going on - the electrons are not non-interacting. | |
| Feb 16, 2015 at 9:50 | comment | added | Level River St | drawing a line through the lowest and rightmost purple points of your graph, I get a gradient of about 0.25/0.8=1/3.2. That isn't so different from the gradient of 1/3 that would be expected on purely geometrical grounds assuming identical density. | |
| Feb 16, 2015 at 8:41 | comment | added | ProfRob | @Aron the density in the centres of stars increases with decreasing mass. It is the core temperature that determines if and when fusion can take place. It never gets high enough in brown dwarfs and planets. | |
| Feb 16, 2015 at 6:28 | comment | added | user10851 | @Aron Fusion requires high temperatures, and the Chandrasekhar mass is 1.4 solar masses. Neither is applicable in the case of anything reasonably called a planet, whereas degeneracy in fact is important starting around a Jupiter mass. | |
| Feb 16, 2015 at 4:04 | comment | added | Aron | I can't help but feel that when we get up to Electron degeneracy, we would a) have surpassed fusion requirements b) be in the regime of Chandrasekhar masses... | |
| Feb 16, 2015 at 0:08 | history | answered | ProfRob | CC BY-SA 3.0 |