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Stellarator
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27 Sep 2019 23:26

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Watsisname
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11 Oct 2019 13:30



Fantastic talk (though a bit more technical than most that I post here) and review of our current understanding of an old astrophysics problem: "Why do some stars explode?"  More precisely, what exactly is going on during the core collapse that allows the ensuing shockwave to reach the star's surface, rather than stall?  If you think this should be trivial, you'd be surprised!
 
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13 Oct 2019 02:13

Watsisname wrote:


Fantastic talk (though a bit more technical than most that I post here) and review of our current understanding of an old astrophysics problem: "Why do some stars explode?"  More precisely, what exactly is going on during the core collapse that allows the ensuing shockwave to reach the star's surface, rather than stall?  If you think this should be trivial, you'd be surprised!

Far from being trivial, isn't this how most elements beyond Iron get produced?  We are indeed made of star stuff!
 
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Watsisname
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13 Oct 2019 03:07

A-L-E-X wrote:
Source of the post Far from being trivial, isn't this how most elements beyond Iron get produced? 

Actually no, most elements above atomic number 40 came from colliding neutron stars rather than exploding stars.

But what I mean about it not being trivial is the question of how does the star explode?  Most people know that they do, and are familiar with the common explanation for how it happens.  But if you do a naive (or even a very sophisticated) application of physics to explain how it works, you will conclude that the shockwave would stall before reaching the surface.  How a star actually explodes was an astrophysics mystery for many decades.  

What we're finding with the latest high resolution 3D supercomputer simulations is that the physics happening is a lot more complex (and very fascinating), and it turns out that turbulence and huge deviations from spherical symmetry are important, in addition to the momentum transported by the neutrinos (which we suspected, but it wasn't enough), and the structure of the star itself.
 
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13 Oct 2019 03:17

Watsisname wrote:
A-L-E-X wrote:
Source of the post Far from being trivial, isn't this how most elements beyond Iron get produced? 

Actually no, most elements above atomic number 40 came from colliding neutron stars rather than exploding stars.

But what I mean about it not being trivial is the question of how does the star explode?  Most people know that they do, and are familiar with the common explanation for how it happens.  But if you do a naive (or even a very sophisticated) application of physics to explain how it works, you will conclude that the shockwave would stall before reaching the surface.  How a star actually explodes was an astrophysics mystery for many decades.  

What we're finding with the latest high resolution 3D supercomputer simulations is that the physics happening is a lot more complex (and very fascinating), and it turns out that turbulence and huge deviations from spherical symmetry are important, in addition to the momentum transported by the neutrinos (which we suspected, but it wasn't enough), and the structure of the star itself.

Ah, I thought that higher atomic number elements (like gold, silver, platinum, even uranium and beyond) get produced in supernova explosions and thats how we happened to have these on our planet (because the cloud from which our sun originated was the result of a supernova explosion?)
That's a very interesting link, neutrinos and the geometry of the star seem to be vital in transporting the energy to the surface.
Secondary question- since there are different types of supernova explosions and even hypernovae, what's the determining factor in the type of explosion that will happen?  Also, are there cases where stars are on the brink of exploding but never explode or explosions that never actually reach the surface?  Whats the final result of that?  Does the interior collapse and the outer part of the star becomes like a "ghost shell" that expands outwards and eventually fades from view as it expands?
 
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14 Nov 2019 00:57



Abstract:
To date, Hubble has played the definitive role in the characterization of exoplanet atmospheres. From the first planets available, we have learned that their atmospheres are incredibly diverse. With HST, JWST, and TESS a new era of atmospheric studies is opening up, where wide scale comparative planetology is now possible. Such studies can provide insight into the underlying physical process through comparative studies. Hubble’s full spectroscopic capabilities are now being used to produce the first large-scale, simultaneous UVOIR comparative study of 20 exoplanets ranging from super-Earth to Neptune and Jupiter sizes. With full UV to infrared wavelength coverage, an entire planet’s atmosphere can be probed simultaneously and with sufficient numbers of planets, it will be possible to statistically compare their features with physical parameters. The panchromatic treasury program aims at build a lasting HST legacy, providing the UV and blue-optical exoplanet spectra which will be unavailable to JWST, providing key insights into clouds and mass loss. I will review the highlights of the program to date, which include atmospheric water resolved in emission and new absorption features seen in transmission such as escaping ionized metals. I will also present the latest findings from the ongoing Hubble Treasury program and discuss synergies with JWST.

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