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Stellar Evolution

The Milky Way galaxy contains several hundred billion stars of various ages, sizes and masses. A star forms when a dense cloud of gas collapses until nuclear reactions begin deep in the interior of the cloud and provide enough energy to halt the collapse

Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years (for the most massive) to trillions of years (for the least massive), considerably more than the age of the universe.    LEARN MORE »

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Interactive Tour: Stellar Evolution Last Updated on 2009-11-26 00:00:00 The Milky Way galaxy contains several hundred billion stars of various ages, sizes and masses. A star forms when a dense cloud of gas collapses until nuclear reactions begin deep in the interior of the cloud and provide enough energy to halt the collapse. Many factors influence the rate of evolution, the evolutionary path and the nature of the final remnant. By far the most important of these is the initial mass of the star. This interactive piece illustrates in a general way how stars of different masses evolve and whether the final remnant will be a white dwarf, neutron star, or black hole. Click link below for an intereactive tour on Stellar Evolution... (also available in pdf form)   More »
Stellar evolution Last Updated on 2009-11-26 00:00:00 Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years (for the most massive) to trillions of years (for the least massive), considerably more than the age of the universe. Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at the various points in their life, and by simulating stellar structure with computer models. All stars form from clouds of gas and dust condensing in deep space.  Only the chemical composition of this cloud, and the amount of material in the cloud that condenses into the actual star, determines what will happen to the star... More »
Stellar Evolution - A History of Discovery Last Updated on 2007-11-26 00:00:00 In 1906, Karl Schwarzschild published a fundamental paper in astronomy, describing the appearance of an incandescent, stable ball of gas in considerable detail, using basic principles in physics. Not only did he show that the sun's limb should be darkened to the precise degree observed, but went on to prove that the distribution of matter within the sun could be determined once you could specify the exact dependency of the gas pressure on its temperature and density. He also discovered that, under certain conditions, energy would be transported from the center of the star outwards, either by the convective boiling motion of matter, or by the streaming of radiation from the core to the surface. Sir Arthur Eddington continued this work by including the affects of radiation pressure, showing that stars that are mechanically stable are only possible for certain combinations of mass and... More »
Sun: Death Last Updated on 2007-11-26 00:00:00 Once our Sun began to produce energy in its core by fusing hydrogen into helium, it embarked on a long 'middle age.'  As the nuclear fires became more efficient, the infant Sun began to expand very slowly. At first the Sun only shone with 70% of its modern brightness. But as it continued to evolve over eons of time, its brightness grew by 7% every billion years. When trilobites first crawled on shallow ocean bottoms 500 million years ago, the Sun was much fainter in the sky than it is today. Earth would have been in a deep-freeze had it not been for the warming actions of an atmosphere laced with trace gases like water and carbon dioxide. In the eons to come, the Sun will continue to expand and shine more brightly for the next 6 billion years. Then a major physical change will start to happen with unprecedented speed. The inner core has become heavily laden with the helium... More »
Sun: Middle Age Last Updated on 2007-11-26 00:00:00 Once our sun began to produce energy in its core by fusing hydrogen into helium, it embarked on a long 'middle age' . As the nuclear fires became more efficient, the infant sun began to expand very slowly. At first the sun only shone with 70% of its modern brightness. But as it continued to evolve over eons of time, its brightness grew by 7% every billion years. When trilobites first crawled on shallow ocean bottoms 500 million years ago, the sun was much fainter in the sky than it is today. Earth would have been in a deep-freeze had it not been for the warming actions of an atmosphere laced with trace gases like water and carbon dioxide. Our sun today as it appears in the light of hydrogen-alpha.(Courtesy: Institute for Astrophysics, Gottingen.) Our sun has already spent 4.5 billion years as a star, and will continue to shine normally for at least another 6 billion years as a... More »