[mesa-users] rotational asymmetry

Bill Paxton paxton at kitp.ucsb.edu
Mon Apr 20 12:21:20 EDT 2015


one I like is "All models are wrong, but some models are useful."

-b


On Apr 20, 2015, at 8:19 AM, Tomasz Plewa wrote:

> As Richard Hamming said, "The purpose of computing is insight, not numbers."
> 
> Tomek
> --
> On 04/20/15 10:39, Stan Woosley wrote:
>> As Fred Hoyle used to say the only fully accurate representation of the 
>> universe is the universe. Some people think maybe it is one big 
>> simulation.
>> 
>> The art of astrophysics is the art of sufficiently accurate approximation.
>> 
>> Hans Bethe did everything on a slide rule.
>> 
>> 
>> 
>> On Apr 19, 2015, at 10:26 PM, Amber Lauer <alauer1 at tigers.lsu.edu> wrote:
>> 
>>> The largest simulation I'm aware of is Horizon run 23 on Tachyon ii, htttp://astro.kias.re.kr at 3.74 x10^11 particles. 
>>> 
>>> Following his calculation i get 51.89 years.
>>> 
>>> On Sun, Apr 19, 2015 at 10:33 PM, Francis Timmes <fxt44 at mac.com> wrote:
>>> for extra fun, generate an order-of-magnitude estimate
>>> of the cost, in dollars, of doing such a calculation.
>>> 
>>> fxt
>>> 
>>> 
>>> 
>>> 
>>> > On Apr 19, 2015, at 7:24 PM, Matteo Cantiello <matteo at kitp.ucsb.edu> wrote:
>>> >
>>> > Hi Amber,
>>> > Casey Meakin gave a talk at the IAU symposium 252 "The art of stellar evolution in the 21st century" (Sanya 2009)
>>> > where he predicted that, assuming Moore's law,  a fully resolved stellar turbulence calculation will be feasible in ~60 years.
>>> > I suggest you have a look at his argument and maybe update it given current computational resources.
>>> > It could be a fun exercise (and please share this with the mailing list if you find something interesting).
>>> >
>>> > http://arxiv.org/pdf/0806.4542.pdf
>>> >
>>> > Cheers,
>>> >
>>> > -M
>>> >
>>> >
>>> > Matteo Cantiello  |  http://matteocantiello.com/
>>> > Associate Specialist in Astrophysics  | Kavli Institute for Theoretical Physics
>>> > Chief Scientist and Board Member, Authorea  |  https://www.authorea.com/
>>> >
>>> > On Apr 19, 2015, at 6:45 PM, Amber Lauer <alauer1 at tigers.lsu.edu> wrote:
>>> >
>>> >> I thank everyone for their answers, this will help me should this question arise. My understanding is that the reason for our dependence on 1D and sometimes 2D approximations to 3D situations is necessity, not denial. While we would ideally all love to use 3D, particle-for-particle identical models, the computational power and algorithms just aren't there yet. In my paper I project that such capabilities could still be 20 years away.
>>> >>
>>> >> On Sun, Apr 19, 2015 at 10:07 AM, Stan Woosley <woosley at ucolick.org> wrote:
>>> >> Fully agreed and a bit more.
>>> >>
>>> >> Unless rapidly rotating, stars are spheres and to first order, well
>>> >> described in 1D codes. 1D models of the solar interior are quite
>>> >> good, but even there, there are exceptions. Convection, wherever it
>>> >> occurs, is inherently multi-dimensional. It is approximated by
>>> >> parameters (mixing length theory) in a 1D code, that usually work well
>>> >> but not always, especially at the boundaries of those regions. The outer
>>> >> quarter of the sun's radius (2% of its mass) is convective. The
>>> >> solar surface is a seething morass of convective blobs, tangled magnetic
>>> >> fields, reconnection, spots,  flares,  and propagating
>>> >> waves. Entire fields study each of these - e..g. helioseismology.
>>> >>
>>> >> When massive stars die, rotation and symmetry breaking plays a big
>>> >> role. The most extreme case that we know comes from stars are
>>> >> gamma-ray bursts. Narrow jets of relativistic matter moving out
>>> >> along the poles and not at other angles. Even without rotation,
>>> >> neutrino  transport calculations of the explosion require 3D to get
>>> >> the neutrino deposited power at all right.
>>> >>
>>> >> Observations of supernovae and supernova remnants in general
>>> >> show that they are not spheres. Polarization measurements show
>>> >> deformation, and look at any modern picture of the Crab or Cas  A
>>> >> remnants to see how much they differ from spheres.
>>> >>
>>> >> Then there are the more docile effects of differential rotation that
>>> >> affect the sizes of stellar cores, surface abundances, and angular momentum
>>> >> of the compact remnants - Eddington Sweet circulation, dynamical and secular
>>> >> shear, and various other instabilities that make helium cores bigger
>>> >> and enrich the stellar surface with elements made deep within.
>>> >>
>>> >> 1D is often a good approximation and it is cheap and easy, but real stars
>>> >> are 3D.
>>> >>
>>> >> Stan
>>> >>
>>> >>
>>> >>
>>> >> On Apr 19, 2015, at 2:00 AM, Santiago Andres Triana <repepo at gmail.com> wrote:
>>> >>
>>> >> > Hi Amber,
>>> >> >
>>> >> > In the case of rapidly rotating stars the spherical symmetry is lost
>>> >> > (by centrifugal deformation) and therefore the spherical harmonics
>>> >> > that we all know and love are not appropriate to describe pulsations.
>>> >> > A 2D code would be necessary here to describe the equilibrium
>>> >> > structure as well (e.g. the ESTER code). 1D models assume "shellular"
>>> >> > differential rotation (dependent only on radius) while in 2D the
>>> >> > models are allowed to have latitude-dependent differential rotation.
>>> >> > Mixing properties are therefore different. In 1D we treat mixing
>>> >> > mechanisms as diffusion processes, but in reality some of those
>>> >> > processes cannot be described properly as such, e.g. when shear from
>>> >> > differential rotation is latitude dependent.
>>> >> >
>>> >> > This topic is really complex! I would recommend the excellent
>>> >> > monography by A. Maeder (Physics, Formation and Evolution of Rotating
>>> >> > Stars) to have an overview. Hope it helps!
>>> >> >
>>> >> > Cheers,
>>> >> >
>>> >> > Santiago
>>> >> >
>>> >> > On Sun, Apr 19, 2015 at 4:04 AM, Amber Lauer <alauer1 at tigers.lsu.edu> wrote:
>>> >> >> I've been asked a few times to describe what is lost in a 1d model vs 2d or
>>> >> >> even 3d, and the astrophysical answer I got when consulting professors was
>>> >> >> "not much". However, I'm preparing for my general exam and would like to
>>> >> >> have a more thorough answer. Does anyone have any input?
>>> >> >>
>>> >> >> --
>>> >> >> Amber Lauer. M.S. Physics
>>> >> >> PhD Student,
>>> >> >> Dept. of Physics & Astronomy,
>>> >> >> Louisiana State University
>>> >> >>
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>>> >> >
>>> >>
>>> >>
>>> >>
>>> >>
>>> >> --
>>> >> Amber Lauer. M.S. Physics
>>> >> PhD Student,
>>> >> Dept. of Physics & Astronomy,
>>> >> Louisiana State University
>>> >> ------------------------------------------------------------------------------
>>> >> BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT
>>> >> Develop your own process in accordance with the BPMN 2 standard
>>> >> Learn Process modeling best practices with Bonita BPM through live exercises
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>>> 
>>> 
>>> 
>>> -- 
>>> Amber Lauer. M.S. Physics
>>> PhD Student,
>>> Dept. of Physics & Astronomy,
>>> Louisiana State University
>>> !DSPAM:212,553494bd1444222426475! ------------------------------------------------------------------------------
>>> BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT
>>> Develop your own process in accordance with the BPMN 2 standard
>>> Learn Process modeling best practices with Bonita BPM through live exercises
>>> http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- event?utm_
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>> 
>> 
>> 
>> ------------------------------------------------------------------------------
>> BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT
>> Develop your own process in accordance with the BPMN 2 standard
>> Learn Process modeling best practices with Bonita BPM through live exercises
>> http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- event?utm_
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>> 
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> http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- event?utm_
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