Stardust Factory Solves Mystery of Impossible Dust

[telfrow]

<i>Researchers using a "stardust factory" at NASA's Goddard Space Flight Center, Greenbelt, Md., have solved a mystery of how dying stars make silicate dust at high temperatures. Understanding this process helps us understand our origin, because this dust will become part of another generation of stars and planets, just as previous generations of stars contributed dust grains into our solar system that at least on one planet led to life. <br /><br />Dying stars heat up internally while expelling their outer layers of gas into space. The gas expands and cools, allowing some matter in it to condense into dust grains. Observations over the last quarter century show dust grains made of silicon and oxygen (SiO or amorphous silicate grains) condensing at 1,300 degrees Fahrenheit (more than 700 degrees Celsius) in the billowing clouds of gas (nebulae) surrounding old stars. The prevailing theory said that this temperature was too high to condense solid silicate grains - the silicon and oxygen should have remained in the gas. <br /><br />"Even though theory said it was impossible, stars made dust grains at high temperatures anyway -- it was happening right before our eyes," said Dr. Joseph Nuth of Goddard, lead author of a paper on this research recently submitted to the Astrophysical Journal. "So we went to our laboratory at Goddard where we vaporize material in a vacuum and observe how it condenses to see what we were missing." <br /><br />The experiment revealed that the "vapor pressure" at which the dust grains condense was too high in the theory. Just as fog (water vapor) condenses out of the air when the temperature drops or the humidity rises, SiO will condense out of nebular gas at certain temperatures and pressures. Warm air holds more water as gas than cold air, which is why 100 percent humidity -- the amount of water gas required to completely saturate the air -- feels so much more uncomfortable on a hot summer day. Similarly, at high temperatures, it takes more SiO ga</i> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>