Messenger - Vol. 2, No. 3, Page 10
Summer 1993
On Research
Dying white dwarf stars foreshadow our sun's demise

     Using the Hubble space telescope to study white dwarf stars, Harry
Shipman recently discovered a double-star system in which gas and mass were
flowing between one star (a type K star that is cooler than our sun) and a
white dwarf star.
     "For the first time, we have found direct evidence of this
phenomenon," says Shipman, professor of physics and astronomy, who is
principal investigator of an international team of astronomers studying
white dwarf stars. "We continue to discover that these white dwarfs are
fascinatingly different."
     Shipman, who calls his research "stellar geriatrics," studies the late
stages of a star's life in expectation of learning more about the
development and future of our solar system. A white dwarf star is a dying
star, representing what our sun will become in its final stages. White
dwarfs are tiny spheres about one-millionth the volume and one-hundredth
the diameter of our sun, but each one has a mass that is a million times as
great as the Earth.
     "One cup of white dwarf stuff would outweigh 24 elephants," says
     Our sun will not reach the white dwarf stage for another 5 billion
years, says Shipman. Although the process of transformation will take a
long time, it can seriously affect the Earth. "First we fry, then we
freeze," notes Shipman. Our sun will swell to a red giant star 50 to 100
times larger than its current size, and, as it expands, the Earth's
temperature will rise. Eventually, the Earth and all the inner planets will
be engulfed by the sun.
     "We don't want to wait around to observe this firsthand," says
Shipman," so we are carefully observing the phenomena elsewhere in the
     Shipman has been studying the white dwarfs for 10 years, using
telescopes located in space. White dwarfs are very hot stars that emit
extreme ultraviolet light and X-rays that cannot penetrate our atmosphere.
The hottest white dwarf star, called H1504+65, is the seventh brightest
X-ray source in the sky, but it produces such a small amount of light that
it can't be seen by the human eye or with binoculars.
     According to Shipman, the nearest white dwarf star, the Sirius B, is
8.6 light-years away, or 45 trillion miles.
                                   -Michael W. Hail, Delaware '94 Ph.D.