The Death of Stars (Inside The Stars)

The timescale of stellar evolution is very long. The Sun, for example took a few million years just to contract from an interstellar gas cloud to become a main-sequence star. Its lifetime as a main-sequence star is about ten thousand million years, of which it has used about four and a half thousand million years. […]

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Beyond The Main Sequene ( Inside The Stars)

When hydrogen – burning reaction in the core are first fully supplying the radiating energy of the star it is said to be on the zero age main sequence. The star stays in the main-sequence band of the Hertzsprung-Russell diagram as long as it has hydrogen nuclear reactions in its core. In general the layers […]

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The Birth of Stars ( Inside The Stars)

The process of star formation is not well understood but we believe that protostars condense out of the tenuous interstellar gas. With¬out knowing the details we can only make a few general remarks. The material of a typical star smeared out to a typical interstellar density (10~21kgm~3) would occupy a spherical volume about one parsec […]

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The life of a star ( Inside The Stars)

STELLAR EVOLUTION is the study of how a star changes with time. There are three important distinct timescales on which a star may change. These are dynamical, thermal and nuclear timescales. The DYNAMICAL TIMESCALE is the time it would take for the whole star to feel seriously and to react to an absence “of-pressure support. […]

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The Nuclear Powerhouse ( Inside The Stars)

The basic source of nuclear energy lies in the equivalence of mass and energy proposed by Einstein and embodied in relation : E=Mc2 If four hydrogen nuclei fuse together to form a helium nucleus there is a certain amount of mass converted into energy. If we write the small mass difference as ?m then: ?m=4mH […]

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The Source of Stellar Energy ( Inside The Stars)

The existence of the temperature gradient requires a flow and release of energy (luminosity) at the surface of the star. If the star is to remain stable the energy loss at the surface must be balanced by new energy from within. But what is the origin of this energy ? For a simple model of […]

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Controlling The Energy Flow ( Inside The Stars)

The radiation does not leak out quickly because it is connected with the matter through the processes of absorption and emission. In¬deed, as noted above, the typical mean free path of a photon is about 1 cm. A measure of the resistance to radiation is the opacity of the material: this quantity indicates how difficult […]

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Energy Transport Inside Stars ( Inside The Stars)

The pressure force ,which opposes the self gravitation force ,takes the form of a gradient of pressure ; that is to say the pressure higher nearer the centre of the star than further out The thermal structure of a star is related to the heat flowing through it in a complicated way. It turns out […]

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The Behaviour of Stellar Gas ( Inside The Stars)

The state of the gaseous material in a star can be described by various physical quantities such as its pressure, P, temperature, i, and density, p. These quantities do not vary independently. If we change the pressure at some point in a star we also alter the temperature and/or density. Clearly, if we are to […]

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How A Star Holds Itself Together ( Inside The Stars)

The mass of gas in a star is held in place by gravity. A star is said to be self-gravitating, because it contains sufficient mass (typically about a million times that of the Earth) for its own gravitational force-field to be sufficiently strong to keep itself together. A star is also gaseous because, even despite […]

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