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 Shipman. 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 universe." 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.