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Measuring the footprints of violence.

Measuring the footprints of violence

Astronomer Randy A. Kimble had to wait eight years, but he finally completed his gaseous quest -- an elusive measurement of the helium between a hot white dwarf star and Earth, which may reveal the frequency and strength of supernova explosions and other violent outbursts in our corner of the universe.

Using a sounding rocket, Kimble had attempted in 1982 to measure the interstellar helium associated with the white dwarf G191B2B, but the experiment failed. His 25 minutes of observations in 1990, using the Hopkins Ultraviolet Telescope, exceeded by a factor of five the amount of observing time available on a sounding rocket, notes Kimble, of Johns Hopkins University in Baltimore.

The telescope data indicate the density of neutral helium between Earth and the star, notes Arthur F. Davidsen, chief researcher on the Hopkins telescope. But by relying on previous estimates of the total (both neutral and ionized) helium and hydrogen left over from the Big Bang, astronomers can now infer the amount of ionized helium in the local interstellar medium created by more recent violent events. Calculating the abundance of ionized helium may reveal the intensity and frequency of these energetic events.

A stream of galactic cosmic rays, leftover heat from supernova explosions, and intense radiation emitted by unseen neutron stars could all contribute to the ionization of helium in the nearby regions of the Milky Way, Davidsen says.
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Title Annotation:helium in space may reveal the frequency and strength of supernova explosions
Author:Cowen, Ron
Publication:Science News
Date:Jan 5, 1991
Words:234
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