Origin of matter

I could write a book land story about this question that what is the origin of the gaseous matter comprising the stars and galaxies? Surely something cannot be created out of nothing .
 the story will contain many definite truths.
 it will have a lot of extrapolation and it might still leave out several big holes.

 let me begin by first stating some things we now understand rather well . we have found out that the familiar world around us is made up of less than 100 elements. hydrogen, oxygen, nitrogen, iron, carbon, copper, zinc etc right up to Uranium represents examples of elements .

 elements are defined through the number of protons in the nucleus. this we learnt later. first, we learnt to recognise them through their chemical properties .

 it is amazing that whenever we look, the earth ,the moon and the stars or  interstellar and intergalactic space is the very same Limited list of elements are found .

 the richness we see on our planet is all derived from the multitude of ways in which these elements combine .
 this includes oceans, rocks and little Hills And The Mighty Himalayas .

 besides, it also includes all things living - the fantastic world of plants and flowers as also of butterflies and babies . tens of millions of species on earth are all ultimately made up of stuff we are familiar with .
 the magic comes from differences in structure and architecture . much of this structure is the result of forces whose nature we now understand reasonably well .
 this also includes the question "why has nature been constraint to have only 92 elements and not just 20, or as many as 500 "? There are no real exceptions to the rules that govern the world of things we have encountered . perhaps that is not strictly true but almost show .

 we cannot fully understand do not post and ultimate violation but only represent our current inability to comprehend and calculate .
 so now, let us move to question ;

how did all these things come into being?
 The variety they represent does not appear to be arbitrary .there is a deep related - Ness .
therefore, the process of creation also cannot be arbitrary .
Our broad understanding in this regard is the following :

We know by now that given enough concentration of energy, various forms of matter, such as protons neutrons ,electrons etc can be created and can transmute into Each Other .

 Einstein proved that theoretically exactly 100 years ago and this is now well established in a large number of experiments .
the ratio of particles produced depends on the details of interactions and of subsequent decay interactions .
we now understand a great deal in this regard, through decades of theory - making and experiments .

 the question arises as to what are the conditions and sources of such concentrations of energy?

One of the moments where conditions might have existed was the moment of the big bang ,hypothesized to exist at the "beginning" of the universe .

it might also be possible under special conditions involving high concentrations of mass , a scenario favoured by scientist who are not happy with the Big Bang hypothesis .

one should not be too worried about the availability of energy, because it can be shown that the positive energy of the particles produced is balanced by the negative gravitational energy .

 there is no Generally Accepted theory about the reason for the universe deciding to exist .

some people think that it was due to a Quantum fluctuation in space time! If all this is a little baffling do not feel to unhappy .

scientists are still struggling with some of these aspects . but a lot about evolution of matter and energy in subsequent epochs is well understood . we think that the light elements, like deuterium, Helium Lithium and beryllium were produced in the super hot stage like the Big Bang .

the heavier elements were synthesized through thermonuclear reactions inside stars and those heavier than iron during supernova explosion of the stars .

 stars can be considered as element manufacturing factory ; they also produces heat, light and other forms of energy as a byproduct .

our sun is one such element manufacturing factory . all this is not just science fiction or a loose story ,The interactions involved and other aspects of Stellar structure and evolution are fairly well understood .

Stars

Suppose we have a large cloud of dust and gas .it is quite likely that because of random fluctuations or some other causes, some part of this cloud may come to be denser than its neighbourhood ,in that case, the surrounding regions would begin to gravitate towards the denser part. 
This is an accelerating process . denser the inner part, more is its attraction.
We therefore have a situation where the dust and the gas start falling inwards, leading to a compaction of the cloud . 
the following material is subject to collisions leading to heating up of the dense cloud.The gravitational energy is being converted into heat energy. the central part of this cloud will be the hottest .
When we say that a gas is hot, we also imply that its particles are moving with random velocity and continuously colliding with each other . in fact, temperature is a measure of the velocity of these particles.Then something new happens . at very high temperatures, atoms are ionized that we do not have neutral atoms anymore . the most abundant element is hydrogen, which after ionization is broken up into protons and electrons . through a well understood series of nuclear reactions and radioactivity, 4 protons are fused into one Helium nucleus resulting in a lot of energy.Energy is released because the mass of helium nucleus is significantly less than the mass of a Proton . 
this can happen only if the thermal energy of the protons is high enough to overcome the electrostatic repulsion between particles of like charges .as the temperature at the centre of the dense cloud Rises, the rate of the fusion reactions also increases . rising temperature leads to a high gas pressure which is enough to support the inward gravitational pressure . 
At that stage, the dense cloud is stabilized. it has become a star.Our sun is one such star. this Star would keep shining at about the same rate till the hydrogen supply in the core is exhausted.Notice the remarkable mechanism that gives long term stability to stellar furnaces. Any increase in the internal temperature that would increase the energy production would also increase the internal pressure . as a result the Star would expand, leading to a drop in the temperature and ,hence, the rate of energy production . the reverse would happen if the internal temperature decreased .stars are self regulating furnaces.
From the above discussion it should be clear that if the material from which stars are formed is about the same the only thing that controls the brightness of the star is its Mass.
Very heavy stars will be able to compress the centre to much higher temperature before the internal pressure Rises enough to counter the force of the gravitational compression.  a higher temperature also implies that the rate of reactions inside is much higher, resulting in the stars being much brighter. this is a sensitive function .
 it turns out that stars that are 10 times more massive than our Sun would produce energy and consume their hydrogen fuel at such a rate that they live a thousand times less than moderate stars like our Sun .
 even among stars the fat and the spendthrifts do not last long! While we talk about energy production in stars, let us not over look that the Stellar furnace is also creating heavier elements through fusion of light elements .
 we will not go at this time into the details of how and when that happens .we should only say that the stars are believed to be the generators of all chemical elements of mass equal to and greater than carbon.
In the end let me say that nothing is permanent does not even the 'saptarishi' . our life span is too short compared to that of the stars .even our recorded history of a few Thousand Years is minuscule in length .
we humans have not been here for a long enough period to see a significant change in the appearance of the heavens . yes ,the changing relative positions of Stellar conditions can be discerned.Life of star depends upon its mass. Strange as it might seem, bigger the mass shorter is its life! While a star with the mass like our Sun might Shine for about 10 billion years, very heavy stars might die in a few million years . To understand this we have to have a General understanding of the way stars are Bond, how they live and the way they Die.this process does not stop at making of helium from hydrogen but in later stages of the Stellar life, also leads to the synthesis of heavier elements . To be aware of big changes, we have to look at the largest sample of astronomical observations .there we do se reminents of supernova ,neutron stars and evidence of black holes.
 these are all stages of the way some stars and their lives sometimes to be born again in States completely unpredictable at the time of their birth.

Protostar- in a nutshell

The current wisdom about the formation of a star goes something like this. first, you need a lot of matter containing various elements, mostly hydrogen, along with a lot of dust that might be the result of earlier happenings in space. 

Large clouds of such matter are visible in many parts of our Galaxy and in other galaxies in the universe. these clouds roam around, sometimes with turbulent motion, rotating and interacting with other clouds and stars. 
All particles in the cloud interact with each other due to force of gravity.
Fluctuations might lead to situation where the concentration of mass is Greater at some point as compared to the neighbourhood. 
This would lead to more and more particles being drawn towards that point of concentration. the big one continuous to become bigger. As the particles fall in together, the progress accelerates.

While this is happening, we have also to remember that the cloud was originally rotating, howsoever slowly . 
the particles that come from the direction of the axis of rotation can fall straight in towards the centre while those along the equator have to content with the centrifugal force. 
Therefore, the concentration of matter does not lead to a ball but to a disc - like shape. All this might take millions of years .In later stages , the particles falling in begin to collide with each other rather frequently and their energy becomes the chaotic energy of heat. 
Does the gravitational energy is converted to heat ;concentrated near the centre of attraction . 

This heat can be sent through infrared emissions. if the cloud is large enough, the process can proceed towards star formation of the clouds .

Before it gets there you can call the child star only a protostar. the true star phase of its life begins when the interior temperature rises to several million degrees or more . 
At those temperature the kinetic energy of protons and light chemical elements are high enough for thermonuclear reactions to occur ; the energies of particles can overcome the electrostatic repulsion of nuclei. fusion of four protons to form a Helium nucleus and a couple of positrons and some neutrinos can produce more energy per mass unit than any other fuel period ,this is the energy that ultimately enables the protostar to shine, and continue to shine till the fuel inside is exhausted .
 Depending on the mass of the stars that might take a few million years to many billions of years . the heavier ones Shine brighter and die earlier . our sun will continue to give us light and heat for several billion years.

Incidentally ,let us not forget the matter around the edges of the accreting disc . it is believed that planets are coagulated in those regions.

Planets-The Spheres(nutshell)!

Spherical shape of planets

As matter accretes, its gravitational attraction increases. Continous accertion leads to an inward gravitational force that can overwhelm the forces that give solid- state structures their integrity. Under a gravitational force that is large enough, even rocks melt and flow. Each particle on the surface of the aggregate wants to get as close to the centre as possible and the shape of the aggregate tends to become spherical - that is what natural equity or democracy would demand. 
Extremly high mountains- protrusions beyond the spherical surface- are not viable because their weight would make them sink down. When we get to aggregations of planetary levels, the height of the highest mountain is inversely proportional to the mass of the planet. Mars has higher mountains and deeper valleys then does the earth because it is less massive then the Earth, even our tiny satellite, the moon , surpases the earth in this regards, whose highest mountain peak sticks out to a height of barely 9km on a sphere whose diameter is nearly 13,000km.

The spherical shape of heavinly bodies testifies that gravitational force of matter in bulk can overcome all other sustaining forces.

Zero weight - possible???

This innocent sounding question requires some detailed consideration. Scientists distinguish between the words "weight" and "rest mass ". In ordinary life on earth, the two are the same . Rest mass or (more simply, mass) and weight are proportional to each other and the unit of measurement are so choose that they are the same. A weighting balance determine the weight; this is the force with which the earth attracts the object.

However, if the same object is in orbit around the earth, it is freely falling the towards the earth and is weightless. If you were that object and stood on a balance while both you and the balance were orbiting the earth the balance would show a reading of zero. Both the balance and you would be weightless, even though both would have the same mass as they had on the surface of the earth.
Therefore, I will assume that we are  interested in finding out whether there is any entity in the universe that has zero "rest mass"? 
The answer to that the last question is yes, and the very obvious "object", if you can call it that , is light . 

We
Light photon have energy but zero rest mass. In addition, there are other particles called neutrinos that have zero or near zero rest mass. The existence of neutrinos was theoretically postulated to explain certain observations , and experimental evidence has since been gathered for their existence. There is some recent evidence that the neutrino mass may not be exactly zero, but they are very close to being mass-less. 
Mass-less particles have an initial role in the universe. This is obvious as far as light and heat are concerned . It has been found that neutrinos are also central in determining the nature and evolution of the universe.