The life of stars usually begins in the womb of a stellar nursery called a nebula. A place that can be hospital yet competitive, the star starts its cycle as all life, in a struggle. Like male sperm competes for the attentions of the mother’s egg, embryonic stars vie for the nurturing food of interstellar gaseous matter.
Nebulae are simply large clouds of dust and gas (mainly hydrogen.) While there are several types of nebula astronomers agree that some large diffuse nebulae have sufficient gas and dust to produce over 100,000 stars the size of our sun.
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Formation of Stars
Under certain circumstances the gases in a nebula will become heated from the ultraviolet light from a large near-by star. Gas and dust will heat up, stimulate atomic behavior and thereby compress into compact matter. Over millions of years the compaction will continue until the protostar has sufficient mass so that the electron repulsion forces of the compacted hydrogen atoms equals the gravitational forces of the star’s mass – equilibrium. At that point the star starts to burn the very hydrogen it was compacting and “Turns On.”
How do Stars Turn On?
The basic H to He + energy fusion reaction 1H1 + 1H1 → 1H2 + e0 + υ then 1H1 + 1H2 → 2He3 + γ (where υ = neutrino and γ = gamma radiation, high energy photons) is carried out in every star. This conversion of Hydrogen into Helium has the by-product of producing energy and light. Energy and photons travel from the core of the star to the surface where warm energy and bright light spew out into the cosmos.
Size of Stars
The size of stars has seen some exciting recent developments. Until now scientist believed large stars gained their mass by rapidly devouring smaller protostars in the crowded Nebulae. However, according to Dr. Nimesh Patel of the Harvard-Smithsonian Center for Astrophysics, “We’ve found a clear example of an accretion disk around a high-mass protostar, which supports the [accretion disk theory.]” This theory states “…that massive stars develop through the gravitational collapse of a dense core in an interstellar gas cloud via processes similar to the formation of low mass stars.”
As a result this new discovery implies that all stars form the same way, through compaction of dust and gas. The difference is simply the amount of material available in a localized region. The denser the material, the larger the star.
Life of Stars
Stars live hundreds of thousands to tens of billions of years however; the life expectancy of stars has a distinct difference depending on the mass of the star. Large stars tend to live short and violent lives while smaller stars (like our sun) last billions of stable years. But, no matter what the size of the star once the nuclear fuel runs out star death is certain.
The Death of Stars
The death of a star, as with its life is equally dependent on it size. Smaller stars tend to die with a whimper, shedding it outer layers until only a dark core is left. Larger stars have a more dramatic cycle just as they have a more dramatic life.
The Death of Small Stars
When a star runs out of nuclear fuel it begins to collapse under gravity as it did during its birth. This collapse causes an increase in temperature that causes the star to burn helium and temporarily push outward. The star will expand tens of times its original size and in the case of our sun all the inner planets will be consumed.
Simultaneously, large sections of its surface are blown into space until the gravitational forces overcome the reduced thermal forces and implosion begins anew. The mass is insufficient to overcome electron degeneracy and no further collapse can occur. Electron degeneracy, the fact that no two electrons may occupy the same space at the same time, determines the final size of the remaining core.
The Death of Large Stars
Larger stars have a far different result. This first stage is much the same but once the H2 and He fuel is consumed the star will start to burn Carbon. In some cases extremely massive stars will continue to burn Oxygen, Neon, Magnesium, Silicon and Sulfur but all must stop at Iron. The energy needed to burn these heavy elements creates internal temperatures that will swell the star to millions of times the size of our sun. Yet, as long as the internal pressures equal gravitational forces the star will remain in equilibrium.
Unfortunately, the burning process of C, O, Ne, Mg, Si or S produces Fe and that decreases the amount of energy released in the star. As the energy drops the temperature decreases and rate of compression by gravity increases. Eventually the fuel must run out and gravity will win. The massive Red Giant will rapidly collapse on itself until neutron degeneracy occurs in the core. At that point the collapsing material will “bounce” off the neutron core in a massive stellar event – the super nova. What happens to the core is discussed in Black Holes Space/Time Distortion.
The Rebirth of Stars
Once the debris, these heavy elements of Carbon to Sulfur that were created inside the star, are thrown into interstellar space by the forces of the super nova, the cycle is set to begin again. Any dying star expels its material into space; however, the debris of super novae tends to gather rather quickly. In cases like the Crab Nebula, the super novae remnants and the actual nebula are difficult to distinguish.
These elements become the dust and gas that is the material needed to produce new stars. The Circle of Life is complete!
