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Star Death

During most of a star's lifetime, nuclear fusion in the core generates enough outward pressure to exactly balance the inward pull of gravity associated with the star's mass. As the nuclear fuel is exhausted, the outward forces diminish, allowing the gravitation to compress the star inward. Eventually, all possible nuclear fuel is used up and the core collapses.

Jack Welch, Univ. of California at Berkeley, on-camera
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Jack Welch, on-camera, continued
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From the onset of dying, a star discharges material at an accelerating pace. Stellar winds - gases ejected from the dying star's surface - replenish the interstellar medium, providing the fuel for another cycle of starbirth .

Jack Welch, on-camera, continued
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What do Stars Collapse Into?

How far and fast the star collapses is determined by the star's initial mass. If the star is massive enough,it may explode and then collapse into a black hole. If it is less massive, it may become a white dwarf or a neutron star.

Stellar Winds: Chemical Clues to Stardeath

To understand the chemistry and physics of stardeath, researchers researchers study stellar winds at varying distances out from dying stars. The chemical transformations they unravel helps them piece together the dying process.

Millimeter Radio Map of IRC+10216

This millimeter wavelength radiomap of the evolved star IRC+10216 indicates the abundance and velocity of different types of molecules in this dying star's winds. Acting as tracers these molecules enable astronomers to measure temperatures, densities and other physical conditions of the star, its winds, and material in the surrounding environment.

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As the gases in the stellar winds continue to expand, a series of reactions leads to the formation of the tracer molecules. Only when the stellar winds exhibit the correct chemistry can the appropriate reactions occur. Mapping this chemistry tells astronomers which chemical reactions are in progress and where.

What about the chemical processes taking place in the winds earlier on, nearer to the star's surface? How do researchers know what reactions occured back then? By using velocity maps. Knowing the speeds at which the molecules travel outwards, astronomers can determine their locations at earlier times, right up to when they first formed in the stellar winds ejected from the star's surface.

Rather than observing one molecule at a time and taking several observations, astronomers want to observe as many molecules as possible during a single observation run. The flexibility of the BIMA array's spectrometer allows astronomers to do just that. In addition to saving time, collecting multiple data during the same run makes it easier for astronomers to compare the physical conditions between regions of different molecular composition. BIMA array's flexible spectrometer allows them to obtain highly detailed radiomaps of the stellar winds blowing off IRC+10216.

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Copyright © 1995: Board of Trustees, University of Illinois

NCSA. Last modified, 11/11/95