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The Life Cycle of a Star in the Galaxy

Updated on July 24, 2013

The stars that shine in the sky have a lifecycle that is similar to yours and mine. Initially, a chain of events is set in motion that begins the process. When the time is right and every necessary development has occurred, a young star, known as a proto star, is born. Like many newborns, there is energy contained within its fiber that will allow it to grow. This it does until it reaches the Main sequence of its life cycle, characterized by its ability to create a nuclear reaction. The stars ability to conduct such an impressive feat will allow it to have an abundance of the energy necessary for its sustenance and its size and luminosity will grow to epic proportions.

The initial creation of a star begins in the depths of space within a cloud of dust and debris called a Nebula[1]. A nebula consists primarily of hydrogen molecules, with a smaller population of helium molecules, and other assorted materials.[2] When the Nebula collides with outside forces such as super novae, other nearby Nebulas, or even neighboring galaxies, the cloud is pushed together by the impact. When the cloud is pushed together, it becomes more and more dense and the make up of its gravity becomes less stable. If enough force is exerted upon the cloud, it becomes so dense and so heavy that it is overwhelmed by the force of its own gravity and contracts in on itself.

The process of a Nebula contracting in on itself creates smaller, higher density clouds. Often referred to as Bok Globules, named after Bart Bok the man who discovered them in the 1940’s, these clouds are still widely discussed as the details of their exact nature remains a mystery. It is observed that as these globules become more and more dense, the friction within them causes them to radiate heat. As they heat, they create pressure that pushes against the contractive force of gravity. When that radiated pressure equals the pressure that gravity is exerting against it, a balance occurs characterized by a stable increase in the velocity of the movement of molecules that is referred to as a Hydrostatic equilibrium. It is at this point that a very dense Protostar is born, forming at the exact center of the location of the equilibrium.

A Protostar is the form that a star takes in its infancy. It is in the first form that it is categorized as an actual star. It is not, however, a full grown star yet. In order to enter the fully formed stage of its life, a star must create enough heat to generate a nuclear reaction. The process of nuclear fusion, which is generating enough energy to combine two elements, in this case Hydrogen and Helium, into one, creates a burst of energy that will sustain the life of a star. The brightness of the star and the size that it can attain is directly related to its ability to create nuclear fusion. The Protostar will steadily increase its heat output due to the pressure built until the necessary temperature is attained to create fusion. It is the stars mechanism in its move into the Main Sequence of its life-cycle and the necessary next step on its way to becoming a fully matured star.

The Main Sequence of the life of the star comprises the majority of the stars overall lifespan.[3] Throughout this stage, the star will continuously fuse Hydrogen and Helium at its core. The amount of Helium molecules within the core of the star will increase at a steady pace from the very beginning of the Main Sequence Stage. In an attempt to fuse the increasingly available atoms, the star will increase in size and brightness. Its boundaries for growth utterly limitless, the star will burn for millions of years until it depletes the molecules available for fusion, eventually burning itself out and completing its life cycle.

As we know, stars play a key role in the universe. As a species, humans are reliant on a star to provide light and heat, elements that are necessary for the creation and upkeep of human life. Understanding and examining star birth and its subsequent stages of development has aided scientists in the creation of countless new understandings and breakthroughs. Their studies have delved deeply into the questions that surround our very origins and have furthered their understanding of the nature of the universe.

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