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Arches National Park Geology Tour provides an extensive, visually rich description of the geology of Arches, by Deborah Ragland, Ph.D. See our DVD collection.

ExploraTour: A Peek into the Lives of the Stars

This set of images shows the stages of star development.
Click on image for full size
Windows Original.

What happens inside an EGG?

When something disturbs the gas and dust cloud (like a supernova blast nearby in space), pockets of higher density develop. They grow larger forming EEG's (Evaporating Gaseous Globules).

Inside an EGG (Evaporating Gaseous Globule) the gas and dust are denser than in the surrounding dust cloud. Gravity acts to pull the gas and dust even more tightly together and to draw in material from the surrounding cloud. Slowly the density builds up.

The center of the globule becomes hotter under the weight of the outer layers. At these high temperatures, the gas molecules move at high enough speeds that collisions are able to break them up into atoms. As temperatures rise even higher, the atoms lose their electrons and become ions. Pressure and temperature continue to build as fresh material is pulled in from the surrounding cloud -- a protostar is formed inside the EGG.

A protostar with too little mass never becomes a star. It becomes a brown dwarf instead and cools slowly to space, radiating away the gravitational energy from its continuing slow collapse.

However, if the protostar has sufficient mass, the density reaches a critical level and the temperature exceeds 10 million kelvins at the center. At this point, nuclear reactions start converting hydrogen to helium and releasing large amounts of energy. The protostar becomes a star and joins the main sequence on the HR diagram.

The gas and dust that are left around the star are either blown away or form a protoplanetary disk, called a "proplyd" from which planets may eventually emerge.

Last modified May 10, 2010 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA