Saturday, 14 February 2015

star - Formulas for gravitatitional equilibrium

I am trying to calculate at which point gravitational equilibrium sets in for various bodys (planets stars neutron stars etc.) assuming they are perfect spheres. However the radius i get is not equal to what it should be according to wikipedia (i tried for the sun a planet and a neutron star, all of them were off by quite a bit)



below is the example of the neutron star radius i m trying to get



my result (factor) is 1 at:
Radius : 2228588 m
Density: 1.2768744892680034E11 kg / m^3



the wikipedia article about neutron stars says radius of a neutron star is about 12 km and the density about 10 times higher than mine but my result is 2228km which is quite a bit off, so i got a 2 part question:
a) am i calculating all forces i need?
and
b) are the formulas i am using correct?



i took them from wikipedia and / or university slides and i found multiple variations of almost all of them(most of which i actually didnt list below), so i m quite confused as to what is correct



i know that i m using iron as element and i should split it up and convert the protons to neutrons but that would only increase the degegeneracy pressure further resulting in an even bigger radius if i m not mistaken.
heres how i calculated it (everything behind a "!" is a comment that describes what it is):



!radiantion constant  in Wm^-2K-4


$sbolzmann = 5.67036713E-8$



!radiantion constant  in J / K


$kbolzmann = 1.3806485279E-23$



!gravity constant


$GRAVITY = 6.67408E-11$



! 1 mol


$mol = 6.02214085774E23$



! 1 u (atomic mass )in kg


$ u = 1.66053904020E-27$



! mass of 1 electron in kg


$ me = 9.1093835611E-31$



!hydrogen mass


$ mh = 1.00782503223 * u $



!neutron mass


$ mn = 1.00866491585 * u$



! speed of light, in m / s 


$ c = 299792458 $



! plank constant h in kg  *  m^2 / s    


$ hp = 6.62607004081E-34$



! reduced plank constant hr in kg  *  m^2 / s   


$ hpr = frac{hp }{ (PI * 2)}$



$ amount = 79378857878009573048911997815206 $



! iron with 26 protons 30 neutrons


$ element = 26Fe56$



$ elementmass = 55.934936$



$ atoms = amount$



$ neutrons = (56-26) * amount$



$ electrons = 26 * amount$



$ particlecount = atoms + electrons$



!4.4400513610370694E30 kg, about 2.3 Mass of the sun


$Mass = elementmass * amount $



$Radius = 2228588$



$Temperature = 9.45179584120983E-7$



$ fgravitation = frac{GRAVITY * (Mass^2)} { Radius }$



$volume = ((frac{4.0}{ 3.0}) * PI * (Radius^3))$



    !density in particles / m^3


$ particledensity = frac{ particlecount }{ volume}$



$a = 4.0 * frac{sbolzmann}{c}$



    !radiation pressure in  J / m^3


$ rpressure = frac{1.0 }{ 3.0} * a * (Temperature^4)$



    !gas pressure in J / m^3


$ gpressure = particledensity * kbolzmann * Temperature$



    !electron degeneracy pressure 


$ epressure = (frac{(PI^3) * (hpr^2)} { (15 * me)}) * ((frac{3 * electrons} { (volume * PI)})^(frac{5.0 }{ 3.0}))$



    ! electron degeneracy pressure formula 2


$ epressure2 = frac{((PI^2) * (hpr^2))} { (5 * me * (mh^ (frac{5.0 }{ 3.0})))} * ((frac{3.0 }{ PI})^ (frac{2.0 }{ 3.0})) * (( frac{(frac{Mass }{ volume})}{ 1})^ (frac{5.0}{ 3.0}))$



    !neutron degeneracy pressure


$ npressure = frac{(PI^3) * (hpr^2) }{ (15 * me))} * ((frac{3 * neutrons} {(volume * PI)})^(5.0 / 3.0))$



    !neutron degeneracy pressure formula 2


$npressure2 = frac{((3^(frac{10.0}{3.0})) * (hpr^ 2)) }{ (15 * (PI^(frac{1.0} { 3.0})) * (mn^ (frac{8.0} { 3.0})) * (radius^ 5))} * ((frac{Mass} { 4})^(frac{5.0} { 3.0}))$



$totalpressure = gpressure + rpressure + npressure + epressure$



$totalpressureforce = totalpressure * volume$



!if factor = 1 then the body is in equilibrium


$ factor = frac{totalpressureforce }{ fgravitation}$

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