Stars begin as vast clouds of dust mainly hydrogen and helium left over from the supernova and formed Nebula. A good example of such as a dust cloud is the Orion Nebula.
Far from active stars, these nebulae remain cold and monotonous for ages.
These vast clouds can be hundreds of light years across. When some disturbance overcomes this balance and causes the cloud to begin collapsing.
These disturbance may come from a shockwave from a nearby supernova explosion or a distant supernova explosion, collision with another gas cloud, or the pressure wave of a galaxy’s spiral arms passing through the region.
These force moves though the cloud, particles collide and begin to form clumps. Individually, a clump attains more mass and therefore a stronger gravitational pull, attracting even more particles from the surrounding cloud and gets compressed.
As more and more matter falls into the clump, its center grows denser and hotter. Over the course of a million years, the clump grows into a small, dense body called a protostar. It continues to draw in even more gas and grows even hotter.
When the protostar becomes hot enough 6999727ºC. Its hydrogen atoms begin to fuse, producing helium and an outflow of energy in the process.
Material continues to flow into the protostar, providing increased mass and heat.
Now, what type of star it will become depends on amount of matter present in it.
Some object does not have enough mass for stellar ignition and become brown Dwarfs.
If a star has enough material, it can generate enough pressure and temperature at its core to begin fusion "a heavier isotope of hydrogen".
If enough mass collapses into the protostar, a bipolar flow occurs. Two massive gas jets erupt from the protostar as hydrogen fusion begins and blast the remaining gas and dust clear away from its fiery surface.
At this stage newly born star stabilizes. It is the point where its output exceeds its intake. The outward pressure from hydrogen fusion now counteracts gravity's inward pull. It is now a new born star and will remain until it burns through all its fuel.
If a protostar contains the mass of our Sun, or less, it undergoes a proton-proton chain reaction to convert hydrogen to helium. But if the star has about 1.3 times the mass of the Sun, it undergoes a carbon-nitrogen-oxygen cycle to convert hydrogen to helium.
Q. What is the lifespan of newly born stars?
A. It all depends on mass and how quickly it consumes its fule i.e. Hydrogen.
Small red dwarf stars can last hundreds of billions of years, while large supergiants can consume their hydrogen within a few million years and die as supernova.
A star about the size of our sun takes roughly 50 million years to reach main sequence and maintains that level for approximately 10 billion years
This lifespan of sun began roughly 4.6 billion years ago, and will continue for about another 4.5 – 5.5 billion years, when it will deplete its supply of hydrogen, helium the elements will "swell" up, swallow Earth, and eventually die off into a small white dwarf.
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