GS4: The Birth of the Star
Updated: May 13
When the Universe reached its 200 millionth birthday, it contained several, slowly swirling, nebulas which were separated by empty space. Still, through this empty space there was a presence of pull of gravity from one nebulae to another. This pull of gravity reshaped the Universe, slowly and permanently.
Birth of the Carina Nebula (Pillars and Jets HH901/902). Click on the Image to Read More..
Image credits: NASA, Hubble Telescope
All matter exerts gravitational pull- a type of force- on the nearby body. This pull is proportional to the amount of mass contained within a body; larger the mass, greater its pull. In the early Universe, this gravitational pull started sucking surrounding gas and grew in mass and density. As this denser region attracted more gas, the gas compacted into a smaller region and the initial swirling motion of gas transformed into a rotation around an axis. Remember the classical example of an ice skater, as he shrinks his arms inward angular speed increases because of the conservation of angular momentum. As more gas continues to move inward into the smaller volume, the rate of rotation becomes faster and faster. With increased rotation, the nebula evolved into a disk shape because of the increasing centrifugal force.
The balance between gravitational collapse, centrifugal force, and conservation of angular momentum resulted in the majority of the mass losing angular momentum and falling to the center of the disk, eventually to form the proto-star. As more and more matter rained inwards, into the disk, it continued to grow and eventually gravity collapsed the inner portion of the disk into a dense ball. As the gas got pulled into a smaller space, its temperature increased dramatically. Eventually, the central ball of the disk became hot enough to glow, and at this point it became a proto-star. And, the remaining mass of the nebulae clumped into smaller spheres, forming the planets.
The proto-sun went through very rapid evolution in the first 1,00,000 yrs accompanied by high luminosity caused by the heat generated by the contraction. When the compression was approximately over, the sun entered the T-Tauri stage, characterized by less vigorous activity which existed for 10Ma. As soon as the sun started burning, it started emanating solar wind, a stream of charged particles. During the T-Tauri stage nature of the solar wind changed and began to radiate outwards from the sun rather than spirally from the poles.
A proto-star continues to grow by pulling mass from its surrounding and becomes dense with its temperature reaching up to 10 million degrees. At this state, Nuclear fusion occurs where hydrogen nuclei slam together so forcefully that they coalesce to form Helium nuclei. This fusion produces a large amount of energy and mass, leading into a furnace. In this way, the first true star is formed with initiation of nuclear fusion. And this happened 800 million years after the Big Bang, and this also gave rise to the first starlight into the newborn Universe. This process happened again and again, and many first generation stars came into existence.
First-generation stars tended to be very massive, perhaps, 100 times the mass of the sun. Astronomers have shown that the larger the star, the hotter it burns and the faster it runs out of fuel and dies. This happens within a few million years for a huge star, until it becomes a Supernova, a giant explosion that blasts much of the star’s matter back into space. Thus, as the first generation stars formed in the early universe, it eventually transformed into the first generation of supernovas.
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