The life cycle of a star is a process that is not only beautiful but, fascinating to those fortunate ones who have the chance to study the subject. To the uneducated soul, gazing upon the night sky wondering what is out there is not a common thing. But being able to learn about what is really out there and how it became, that my friends, is truly an amazing task. One has to wonder just how we know what type of star we are looking at or at what point in the star’s life cycle the star dwells.
Since the dawn of man, we have studied the stars, and until the last century, astronomers have found ways to measure four properties of stars: their luminosities, temperatures, radii, and masses. With this knowledge, they now have classified thousands of stars by plotting these stars on diagrams and charts characterized by any pair of these specific properties. A Star is Born Stellar Nursery – Nebula The proverbial birth of a star starts within a huge cloud of gas and dust known as a nebula. A nebula is approximately 21 light-years in width.
When the gases and elements of the nebula start to contract due to the pull of its own gravity, it will create a protostar, which can startingly grow to roughly 60 million miles across. This is where the star begins to take shape. In order for a star to grow, it will need nuclear fusion to take place, and that requires tremendous amounts of pressure and heat. Main Sequence Stars The enormous pressure that is created compresses together elements to form more elements and to create energy. With hydrogen being the least dense and easiest to fuse, stars begin fusing hydrogen first.
The side effect of this fusing of nuclei, or nuclear fusion, is the production of two positrons, two neutrinos, and the release of energy. Stars that are in the hydrogen burning process are known to be in the main sequence. Stars will spend the majority of their lifespan in the main sequence. Using the standardized classification system, astronomers find that about 90% of all stars cluster in thin bands on each the noted diagrams. Red Giant Eventually in the star’s life, the hydrogen supply in the core will begin to expire, when this happens, the sun’s core becomes unstable and will begin to contract.
Consequently, the outer shell of the star, which consists mainly of hydrogen, will start to expand. During the expansion, it cools and will begin to glow red. The star now resides a red giant phase of its life cycle (Cain, 2009). Practically all stars will evolve identically up to the red giant phase, yet depending on the amount of mass a star, the next phase in the life cycle can be greatly different. Supergiants One possible evolution of extremely massive stars, although rare, is to become a supergiant. But what is a supergiant?
When the radiation released by the fusion of helium into carbon it causes the red giant to expand even larger, perhaps into a star roughly 400 times the Sun’s size. The End of Days – Death of a Star White Dwarf A white dwarf, or a remnant of a star that has collapsed, are the destiny of stars like our sun. This phase in the life cycle is attained when the nuclear fuel supply is exhausted. Typically, a white dwarf can have the mass of about six-tenths the mass of our sun, but obtains size considerably smaller than that of the Earth.
A white dwarf is formed when the shroud of a red giant is ejected as the core burns the last bits and pieces of its nuclear fuel. A white dwarf slowly fades into oblivion as it cools down. Supernova Possibly, exceedingly massive stars can continue to fuse heavy elements in order to produce more energy. Nevertheless, once iron is formed, it cannot be fused to make more energy. This is because iron has such a high binding energy and is thus very stable. Due to the immense gravity, the core will collapse and huge amounts of gas on the surface will blast out into space.
This phase in the star’s life cycle has now become a supernova. Neutron Star Following a supernova explosion, the iron core of the star may be enormously massive, and may have an immense force of gravity. It has now become a neutron star, where the negative force, or pushing effect, between neutrons stops the contraction caused by gravity. Pulsar It is possible for a neutron star to spin rapidly following a supernova explosion. A result of this spinning, the neutron star may send out two beams of radio waves, light, and X-rays.
These beams radiate in a circle as the star is spinning, and thus appears that the light from the star is pulsing intermittently. This is why it is called a Pulsar. Blackhole Yet some extremely massive supergiants, many with a mass more than four times that of our own Sun, may continue contracting until their nuclei are compacted into even more dense matter. The compacting matter forms a body so dense that it forms a black hole. A black hole is an extremely massive and dense, spectral body with a gravitational pull powerful enough to prevent the escape of light (Newman, 2002).
Life as We Know It Astronomers believe Earth and all its living organisms are composed of elements formed in the interiors of stars, especially supergiants that exploded as supernovas. As astronomers across the globe scour planetary systems, both within and beyond our galaxy, in the quest to find life, they are centering their attention on each system’s habitable zone. The habitable zone is where heat radiated from the star is just right to keep a planet’s water in liquid form (Williams & Pollard, 2000), the sweet spot of the solar system.
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