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What dictates galaxy and planetary system sizes?



 
 
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  #1  
Old December 18th 16, 10:31 PM posted to sci.astro.research
Richard D. Saam
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Posts: 240
Default What dictates galaxy and planetary system sizes?

What are the functional relationships dictating
galactic size (presently ~10^22 cm)
and star planetary system size (presently ~10^15 cm)
contained in a Hubble radius (presently ~10^28 cm)
and the voids between?

Richard D Saam

[[Mod. note -- There is a large body of literature on how planetary
systems form. A key factor is what materials are solid vs gaseous as
a function of temperature (which is closely tied to distance from the
protostar in the protostellar nebula). Alas, I don't seem to have any
good references to hand at this moment. Perhaps someone can suggest
some good review papers? Until then, Wikipedia offers
https://en.wikipedia.org/wiki/Format...em#Format ion
-- jt]]
  #2  
Old December 20th 16, 06:31 AM posted to sci.astro.research
Richard D. Saam
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Posts: 240
Default What dictates galaxy and planetary system sizes?

On 12/18/16 3:31 PM, Richard D. Saam wrote:
What are the functional relationships dictating
galactic size (presently ~10^22 cm)
and star planetary system size (presently ~10^15 cm)
contained in a Hubble radius (presently ~10^28 cm)
and the voids between?

Richard D Saam

[[Mod. note -- There is a large body of literature on how planetary
systems form. A key factor is what materials are solid vs gaseous as
a function of temperature (which is closely tied to distance from the
protostar in the protostellar nebula). Alas, I don't seem to have any
good references to hand at this moment. Perhaps someone can suggest
some good review papers? Until then, Wikipedia offers
https://en.wikipedia.org/wiki/Format...em#Format ion
-- jt]]

That covers planetary system size (presently ~10^15 cm) formation
but is there an inherent planetary system size relationship to
galactic size (presently ~10^22 cm)
and Hubble radius (presently ~10^28 cm)
that can be explained by fundamental parameters
(H,c,h,G,kb) or others?
RDS
  #3  
Old December 21st 16, 01:32 PM posted to sci.astro.research
Phillip Helbig
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Posts: 38
Default What dictates galaxy and planetary system sizes?

In article , "Richard D.
Saam" writes:

What are the functional relationships dictating
galactic size (presently ~10^22 cm)
and star planetary system size (presently ~10^15 cm)
contained in a Hubble radius (presently ~10^28 cm)
and the voids between?


Keep in mind that galaxies range in size over several orders of
magnitude. Also, "size" is difficult to define. Solar systems probably
have a much smaller range in size, but again the precise definition is
not clear.

Sometimes, "numerology" can be used to derive true results, such as the
typical mass of a star. Check out the corresponding chapter in Edward
Harrison's COSMOLOGY textbook.

Keep in mind that the size of the Hubble radius is a) probably not
really relevant here and b) changes with time and c) galaxies evolve
with time. So, at best, you could hope for some very rough estimate
based on the constants of nature and so on. But that's not enough.
Sure, some combination of the constants of nature can reproduce anything
you want; you need to have an explanation as well.

My guess is that there is no such relation. Yes, the quantities are
determined, as is everything, by the constants of nature and by initial
conditions, but there is no reason to expect a simple relationship of
the kind you suggest.
  #4  
Old December 25th 16, 04:47 AM posted to sci.astro.research
Richard D. Saam
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Posts: 240
Default What dictates galaxy and planetary system sizes?

On 12/21/16 6:32 AM, Phillip Helbig (undress to reply) wrote:

Sometimes, "numerology" can be used to derive true results, such as the
typical mass of a star. Check out the corresponding chapter in Edward
Harrison's COSMOLOGY textbook.

Please do not confuse "numerology" with dimensional analysis.
Would you say that the following dimensional equations
properly reflect star dynamics as textually expressed in
Harrison's COSMOLOGY textbook chapter 5 relection 7 ?

[[Mod. note -- These are aren't "dimensional equations" as the
term is usually understood. -- jt]]

dM/dr = 4*pi*rho*r^2
dP/dr = -G*Mr*rho/r^2 (G Newton gravity constant)
P = (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas constant)
dT/dr = alpha*g*T/Cp (alpha,Cp are thermodynamic constants)
luminosity(L) = 4*pi*r^2*stefan_constant*T^4

I can see uncertainties:
1. ideal gas law may not be applicable in this non ideal condition
2. alpha,Cp thermodynamic constants may not be constant with radius(r)

It is interesting to note in reflection 7
that Newton did not actually use
the Newton dimensional gravity constant
as we know it.

Richard D Saam
  #5  
Old December 25th 16, 05:26 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default What dictates galaxy and planetary system sizes?

In article , "Richard D.
Saam" writes:

Sometimes, "numerology" can be used to derive true results, such as the
typical mass of a star. Check out the corresponding chapter in Edward
Harrison's COSMOLOGY textbook.

Please do not confuse "numerology" with dimensional analysis.


Dimensional analysis is the consideration that a certain quantity must
depend on various constants of nature and so on; a combination with the
proper dimensions is often right to within a factor of order unity.
Numerology is usually a pejorative term for fooling around with various
combinations of quantities until, by chance, some coincidence is found,
then interpreting this as having some sort of deep meaning. My
"numerology" (in quotes) is the more serious form of this, i.e. DERIVING
the order of magnitude of something (say, the mass of a star) from
general arguments. There is an entire chapter in Harrison's textbook on
this. It needs more physics input that dimensional analysis.

Would you say that the following dimensional equations
properly reflect star dynamics as textually expressed in
Harrison's COSMOLOGY textbook chapter 5 relection 7 ?

[[Mod. note -- These are aren't "dimensional equations" as the
term is usually understood. -- jt]]


Right; they are differential equations.

dM/dr = 4*pi*rho*r^2
dP/dr = -G*Mr*rho/r^2 (G Newton gravity constant)
P = (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas constant)
dT/dr = alpha*g*T/Cp (alpha,Cp are thermodynamic constants)
luminosity(L) = 4*pi*r^2*stefan_constant*T^4

I can see uncertainties:
1. ideal gas law may not be applicable in this non ideal condition
2. alpha,Cp thermodynamic constants may not be constant with radius(r)


Sure, but this is covered in any book on stellar structure and
evolution, such as Kippenhahn and Weigert.
  #6  
Old December 25th 16, 08:27 PM posted to sci.astro.research
Daniel S. Riley
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Posts: 4
Default What dictates galaxy and planetary system sizes?

"Phillip Helbig (undress to reply)"
writes:
My "numerology" (in quotes) is the more serious form of this,
i.e. DERIVING the order of magnitude of something (say, the mass of a
star) from general arguments.


Sometimes known as order, Fermi, or "back of the envelope" estimates:

https://en.wikipedia.org/wiki/Back-o...pe_calculation

I don't really like calling those "numerology", even in scare quotes.
Fermi estimates are motivated by the fundamentals of the relevant
physics, while numerology is all about particular values and not at
all about fundamentals.

-dan

  #7  
Old December 26th 16, 11:25 AM posted to sci.astro.research
Richard D. Saam
external usenet poster
 
Posts: 240
Default What dictates galaxy and planetary system sizes?

On 12/25/16 10:26 AM, Phillip Helbig (undress to reply) wrote:
In article , "Richard D.
Saam" writes:

Sometimes, "numerology" can be used to derive true results, such as the
typical mass of a star. Check out the corresponding chapter in Edward
Harrison's COSMOLOGY textbook.

Please do not confuse "numerology" with dimensional analysis.


Dimensional analysis is the consideration that a certain quantity must
depend on various constants of nature and so on; a combination with the
proper dimensions is often right to within a factor of order unity.
Numerology is usually a pejorative term for fooling around with various
combinations of quantities until, by chance, some coincidence is found,
then interpreting this as having some sort of deep meaning. My
"numerology" (in quotes) is the more serious form of this, i.e. DERIVING
the order of magnitude of something (say, the mass of a star) from
general arguments. There is an entire chapter in Harrison's textbook on
this. It needs more physics input that dimensional analysis.


Your logic indicates all physical analysis
is some degree of "numerology"
which in the case of star mass is "serious form".
By this definition, "numerology"
can be used as a paper review scare tactic to which
there is no defense. To what degree of "numerology" is implied?
Whereas if the reviewed work is based on dimensional analysis
one can argue this or that dimension is correct or not
in the context of real data.
I think that Harrison would be offended
having any of his work (including chapter 26)
termed "numerology".

Would you say that the following dimensional equations
properly reflect star dynamics as textually expressed in
Harrison's COSMOLOGY textbook chapter 5 relection 7 ?

[[Mod. note -- These are aren't "dimensional equations" as the
term is usually understood. -- jt]]


Right; they are differential equations.


Differential equations also may be properly expressed
in dimensional analysis.
jt possibly meant something else.


dM/dr = 4*pi*rho*r^2
dP/dr = -G*Mr*rho/r^2 (G Newton gravity constant)
P = (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas constant)
dT/dr = alpha*g*T/Cp (alpha,Cp are thermodynamic constants)
luminosity(L) = 4*pi*r^2*stefan_constant*T^4

I can see uncertainties:
1. ideal gas law may not be applicable in this non ideal condition
2. alpha,Cp thermodynamic constants may not be constant with radius(r)


Sure, but this is covered in any book on stellar structure and
evolution, such as Kippenhahn and Weigert.


  #8  
Old December 26th 16, 06:25 PM posted to sci.astro.research
Richard D. Saam
external usenet poster
 
Posts: 240
Default What dictates galaxy and planetary system sizes?

On 12/25/16 1:27 PM, Daniel S. Riley wrote:
"Phillip Helbig (undress to reply)"
writes:
My "numerology" (in quotes) is the more serious form of this,
i.e. DERIVING the order of magnitude of something (say, the mass of a
star) from general arguments.


Sometimes known as order, Fermi, or "back of the envelope" estimates:

https://en.wikipedia.org/wiki/Back-o...pe_calculation

I don't really like calling those "numerology", even in scare quotes.
Fermi estimates are motivated by the fundamentals of the relevant
physics, while numerology is all about particular values and not at
all about fundamentals.

-dan

I have found it refreshing
to look out of an airplane cabin window onto the wing
and with a "back of the envelope" calculation
establish that I should actually be flying
within the multi ton piece of metal
contain several hundred people.

And calculations are not done with "numerology".

Richard D Saam
  #9  
Old December 26th 16, 06:25 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default What dictates galaxy and planetary system sizes?

In article , "Richard D.
Saam" writes:

On 12/25/16 10:26 AM, Phillip Helbig (undress to reply) wrote:
In article , "Richard D.
Saam" writes:

Sometimes, "numerology" can be used to derive true results, such as t=

he
typical mass of a star. Check out the corresponding chapter in Edwar=

d
Harrison's COSMOLOGY textbook.

Please do not confuse "numerology" with dimensional analysis.


Dimensional analysis is the consideration that a certain quantity must
depend on various constants of nature and so on; a combination with the
proper dimensions is often right to within a factor of order unity.
Numerology is usually a pejorative term for fooling around with various
combinations of quantities until, by chance, some coincidence is found,
then interpreting this as having some sort of deep meaning. My
"numerology" (in quotes) is the more serious form of this, i.e. DERIVIN=

G
the order of magnitude of something (say, the mass of a star) from
general arguments. There is an entire chapter in Harrison's textbook o=

n
this. It needs more physics input that dimensional analysis.


Your logic indicates all physical analysis
is some degree of "numerology"
which in the case of star mass is "serious form".


In some sense, yes. Note that the scare quotes are there because this
is NOT what is generally known as numerology, although it might look
superficially similar. Certainly all physical analysis must include
"numerology" in that the order of magnitude must be correct, it must
follow from simple principles, etc. In some cases, that is enough; that
is what I meant by the example of Harrison's "numerology". In other
cases, it isn't, because the processes are more complicated.

By this definition, "numerology"
can be used as a paper review scare tactic to which
there is no defense. To what degree of "numerology" is implied?


Not sure what you mean here. If a back-of-the-envelope calculation
indicates that some result is obviously wrong, then OK. There is of
course no defense in that there is nothing worth defending. However, it
can't be used to discredit ANY claim.

Whereas if the reviewed work is based on dimensional analysis
one can argue this or that dimension is correct or not
in the context of real data.


Sure; if the dimensions are wrong, the result is wrong. If the
dimensions are right, then the answer is not necessarily right.

I think that Harrison would be offended
having any of his work (including chapter 26)
termed "numerology".


The term doesn't matter, as long as it is understood. Perhaps
"back-of-the-envelope calculation" is better.

Would you say that the following dimensional equations
properly reflect star dynamics as textually expressed in
Harrison's COSMOLOGY textbook chapter 5 relection 7 ?

[[Mod. note -- These are aren't "dimensional equations" as the
term is usually understood. -- jt]]


Right; they are differential equations.


Differential equations also may be properly expressed
in dimensional analysis.
jt possibly meant something else.


I don't think so. Of course, ANY equation has to get the dimensions
right.

dM/dr =3D 4*pi*rho*r^2
dP/dr =3D -G*Mr*rho/r^2 (G Newton gravity constant)
P =3D (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas consta=

nt)
dT/dr =3D alpha*g*T/Cp (alpha,Cp are thermodynamic constants)
luminosity(L) =3D 4*pi*r^2*stefan_constant*T^4

I can see uncertainties:
1. ideal gas law may not be applicable in this non ideal condition
2. alpha,Cp thermodynamic constants may not be constant with radius(r)


Sure, but this is covered in any book on stellar structure and
evolution, such as Kippenhahn and Weigert.

  #10  
Old January 3rd 17, 09:10 PM posted to sci.astro.research
jacobnavia
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Posts: 105
Default What dictates galaxy and planetary system sizes?

Le 21/12/2016 à 13:32, Phillip Helbig (undress to reply) a écrit :
the quantities are
determined, as is everything, by the constants of nature and by initial
conditions,


Since most of the mass of a planetary system is in the star, the limit
to its mass is the limit of the mass of a star.

Now, stars when they become obese, start producing antimatter that
destroys the star before it is fully built, the limit on star sizes
determines, as a consequence, the size of the planetary systems...

Is that correct?

 




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