[mesa-users] A common stellar-structure myth

Tomasz Plewa tomekplewa at gmail.com
Wed Aug 31 08:25:23 EDT 2016


The energy generation, actually, which is a locally controlled quantity. 
If one wishes to simplify the picture so much and discuss the energy 
generation rate based on two stellar profiles, the gravity is merely the 
means and not the outcome.

My point was that the misconception involved gravity (gravitational 
acceleration) while the gravitational potential appears more important 
because the material (has been brought in from infinity and) 
gravitationally heated up. If the compression process is instantaneous 
(or fast enough so we can neglect other processes - vide the ignition of 
a white dwarf passing by a black hole), the virial theorem applies. It 
is not sufficient to describe the stellar structure, but correctly 
reflects on the the essential component.

Tomek
--
On 08/30/16 23:56, RICHARD H D TOWNSEND wrote:
> But it *did* involve the luminosities of the two stellar profiles, and the virial theorem is insufficient to calculate those luminosities.
>
> cheers,
>
> Rich
>
>> On Aug 30, 2016, at 9:47 PM, Tomasz Plewa <tomekplewa at gmail.com> wrote:
>>
>> The original problem did not involve time, but two stellar profiles.
>>
>> Tomek
>> --
>>
>>
>>> On Aug 30, 2016, at 10:27 PM, RICHARD H D TOWNSEND <townsend at astro.wisc.edu> wrote:
>>>
>>> But the virial theorem is insufficient, since it only gives the instantaneous relationship between thermal and gravitational energies. It does not indicate how these quantities vary with time — i.e., the star’s luminosity.
>>>
>>> cheers,
>>>
>>> Rich
>>>
>>>> On Aug 30, 2016, at 9:14 PM, Tomasz Plewa <tomekplewa at gmail.com> wrote:
>>>>
>>>> The problem does not involve time. Then we may not need anything more than the virial theorem to solve it.
>>>>
>>>> Tomek
>>>> --
>>>>
>>>>
>>>>> On Aug 30, 2016, at 6:17 PM, RICHARD H D TOWNSEND <townsend at astro.wisc.edu> wrote:
>>>>>
>>>>> That’s as maybe, but the gravity is not stronger.
>>>>>
>>>>> In any case, what really drives the large energy generation rate in massive stars is the energy loss rate through the stellar surface, which scale as L ~ M^3 (independent of nuclear reactions). The pre-MS star continues to contract until the core energy generation rate matches this loss rate.
>>>>>
>>>>> cheers,
>>>>>
>>>>> Rich
>>>>>
>>>>>> On Aug 30, 2016, at 5:05 PM, Tomasz Plewa <tomekplewa at gmail.com> wrote:
>>>>>>
>>>>>> It's a deeper potential well.
>>>>>>
>>>>>> Tomek
>>>>>> --
>>>>>>
>>>>>>
>>>>>>> On Aug 30, 2016, at 5:52 PM, RICHARD H D TOWNSEND <townsend at astro.wisc.edu> wrote:
>>>>>>>
>>>>>>> Hi folks —
>>>>>>>
>>>>>>> While reading the textbook I’m going to be teaching from this semester (“Pathways to Astronomy”, by Schneider & Arny), I came across this common myth about stellar structure:
>>>>>>>
>>>>>>> “The stronger gravity of a more massive star drives up the rate of nuclear fusion dramatically, while smaller stars consume their fuel at a more leisurely pace”.
>>>>>>>
>>>>>>> The attached figure, courtesy of MESA, shows the internal gravity for 1Msun and 10Msun stars at the ZAMS — and nicely busts the myth.
>>>>>>>
>>>>>>> cheers,
>>>>>>>
>>>>>>> Rich
>>>>>>>
>>>>>>> <gravity.pdf>
>>>>>>> ------------------------------------------------------------------------------
>>>>>>> _______________________________________________
>>>>>>> mesa-users mailing list
>>>>>>> mesa-users at lists.sourceforge.net
>>>>>>> https://lists.sourceforge.net/lists/listinfo/mesa-users





More information about the Mesa-users mailing list