Making medium-weight elements now.
The universe has 92 naturally occurring chemical elements. Astrophysicists and nuclear physicists together have concluded that the universe started out with only hydrogen and its isotope deuterium. Ordinary processes in the more common kinds of stars make the lighter elements, up to about carbon and oxygen. Heavier ones must come from unusual events, such as stellar explosions, or more exotic kinds of stars or stellar objects, but no one is quite sure of the details. In gamma-ray spectra taken by the HEAO 3 satellite Alan S. Jacobson of Caltech's Jet Propulsion Laboratory in Pasadena now finds the first direct evidence that synthesis of medium-weight elements is now going on in interstellar space.
The gamma-ray spectrometer on HEAO 3 found radiation with an energy of 1,808 kilo-electron-volts coming from the direction of the center of our galaxy. This energy is characteristic of radioactive aluminum-26, an isotope with a lifetime of about a million years. The shortness of the lifetime combined with the strength of the radiation indicates that the aluminum is being formed now. Observations with the Solar Maximum Mission satellite have lately confirmed the HEAO 3 finding, Jacobson says.
Probably the most popular theory of the formation of medium-weight elements like aluminum proposes that they are made in shock waves that arise during the explosion of a star into a supernova. However, Jacobson says, the amount of aluminum seen is about three times what would be expected if supernovas were the sole source. Other possible sources, he says, are novas (another kind of stellar explosion), red giant stars, Wolf-Rayet stars or stars of spectral class O. According to Jacobson, novas are most likely.
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|Title Annotation:||synthesis of medium-weight elements is now going on in interstellar space|
|Author:||Thomsen, Dietrick E.|
|Date:||Jul 19, 1986|
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