Dear Mr. Murthy,

We do understand the many physical processes involved for galaxy formation, the gravitational dynamics of matter clustering, the radiative processes, thermonuclear processes once stars form and some explode at the end of their lives. Maybe there is a supermassive black-hole that forms. Then we have to contend with both baryonic matter and (dark) non-baryonic matter. This clustering process starts and continues in an expanding universe. We have also observed in the Cosmic Microwave Background (CMB) the density fluctuations in the very early universe that are presumably the seeds of galaxy formation.

Thus, the complexity lends to a very involved model that is numerically calculated and we get structures resembling the galaxies we see. During Feynman's time the computing power did not exist to make such a detailed model. We are still far from a completely satisfactory model that explains a galaxy's structure at all scales and naturally produces the stars and chemical abundances etc. But it is an ongoing process to model galaxies.

Suketu Bhavsar

Dear Peela,

   I hope the following links to be helpful.

Best Luck

http://iopscience.iop.org/article/10.1088/1742-6596/722/1/012023/pdf

https://arxiv.org/pdf/1412.2712.pdf

http://people.umass.edu/hjmo/teaching/astro330/htmldir/reading.pdf

http://www.sciencedirect.com/science/article/pii/S2090997712000090/pdfft?md5=7c242db8752d12549d2670428b6fa394&pid=1-s2.0-S2090997712000090-main.pdf

http://www.kof.zcu.cz/st/dis/schwarzmeier/galaxy_models.html

thank you Mr. Khaled

Dear Mr. Murthy,

We do understand the many physical processes involved for galaxy formation, the gravitational dynamics of matter clustering, the radiative processes, thermonuclear processes once stars form and some explode at the end of their lives. Maybe there is a supermassive black-hole that forms. Then we have to contend with both baryonic matter and (dark) non-baryonic matter. This clustering process starts and continues in an expanding universe. We have also observed in the Cosmic Microwave Background (CMB) the density fluctuations in the very early universe that are presumably the seeds of galaxy formation.

Thus, the complexity lends to a very involved model that is numerically calculated and we get structures resembling the galaxies we see. During Feynman's time the computing power did not exist to make such a detailed model. We are still far from a completely satisfactory model that explains a galaxy's structure at all scales and naturally produces the stars and chemical abundances etc. But it is an ongoing process to model galaxies.

Suketu Bhavsar

Couple of my observations:

Existence of black holes is questionable. There are 4 types of black holes in scientific literature. What type of the black hole is taken into account? The CMB turns out manipulated. See https://www.youtube.com/watch?v=Y8FsfFs_nvM 

Universe does not expand in contrast to motion of galaxies that some approach and some move away from each other (within universal nucleus).

So-called "early universe" never existed. The universe has no age (it Was-Is-Will be). We can talk only about material universe in contrast to pre-material one. The latter gave birth to the first (some 14 billion years ago - if properly calculated. Obviously not from the nonsensical and microscopic squeeze but from primordial looseness).

In science we explain phenomena by means of objects. Math describes dynamics. Quote from  http://rationalsciencemethod.blogspot.co.uk/2012/12/the-rational-scientific-method.html :  "Science is about explaining. Science, in general, and Physics in particular, is about physically present objects. Understanding the difference between objects, and concepts allows one to rationally make a conclusion about the Key Terms, and the statement of facts at the hypothesis stage of the Scientific Method. Proof is for math. Science never proves. Science is about physical reality. Math describes abstract dynamic concepts whereas science illustrates static physical objects, and explains phenomena."

Dear Mr Murthy,

You will also find interesting information in the joined document « Galaxy formation model_2014 » and on the webpages of Max-Planck-Institut für extraterrestrische Physik (MPE) – Garching :

http://www.mpe.mpg.de/2169/en

http://www.mpe.mpg.de/2169/en

Dear Mr Murthy,

I also join the Scientific report 2007 – 2012 of MPE-Garching (it didn't pass in my former post). This report contains elements which could interest you : e.g. Chapter 2 (pp. 13 …) : mainly 2.2, 2.3 – Paragraphs 4.2, Chapter 6 etc… And lists of publications.

As a personal comment on the formation and evolution of galaxies, I have extracted following Fig-IR2 from p. 16 of this report because I find it interesting as it triggers thinking. It shows the star formation density in function of the time since the Big Bang starting from now (or equivalently in function of the redshift « z »). One observes strong non-linearities in this curve : a first « accretion epoch » around 1-2 Gyrs since the Big Bang (BB), where the star formation density steeply increases, then a peak around 3-4 Gyrs, followed by a long period of winding (dropping) down from say 5 Gyrs after the BB until now. As I understand it, for « Main Sequence » star forming galaxies (the case here), the star formation density is proportional to the stellar mass per unit galaxy volume. It should hold or continue to increase, not decrease.  Drop down gives the feeling of a kind of « progressive exhaustion » of the star formation capacity. Could somebody reading this thread enlighten this point and give hints on a correct interpretation to this phenomenon ? Maybe Dr Bhavsar on base of their modelling and computations ?

Thanks for the question.

I have some idea regarding this.Astrophysics is a branch of Astronomy(space science) that applies the laws of physics and chemistry to explain the birth,life and death of stars,planets and galaxies.The important mathematical model in astrophysics is Lane-Emden equation which is a singular boundary value problem.

   As far as I know, the Lane- Emden equation is for stellar interiors; I don´t think it can be easily generalized to other astronomical objects. (I guess it all depends on the boundary conditions.)

Raul, You are correct. And it was very useful before numerical computational approaches became so powerful. It is a dimensionless equation for a self-gravitating sphere and certain features of such a sphere can be derived for different polytopes. Very instructional but limited in scope.

   Thank you, Suketu. I tried to solve it analytically when I was a student of astrophysics. I didn´t know it was somewhat outdated today.