The evolution of the intermediate-mass stars is a good example of the process by which stars are born, live, and die. This star begins as a swirling cloud of gas that takes 100,000 years to collapse into a protostar. Hydrogen fusion begins in the protostar and causes the creation of a T-Tauri star which is a variable brightness star. This new star contracts for 10 million years until the core energy is balanced with gravity. "The star has begun the longest part of its life as a producer of energy from hydrogen fusion, the main-sequence phase...The amount of time a star spends there depends on its mass" but is likely to be billions of years (Green, 2005, p. 6). When the balance between the production of fusion energy and gravity shifts, compression occurs and the star enters the "red giant" phase where it expands greatly and appears red in color. Another 100 million years brings another change and the star enters horizontal branch phase in which it grows smaller and burns steadily. The star endures another expansion and greater weakening in the next "asymptotic giant phase" and eventually becomes a "white dwarf" resembling a planet. The last phase for an intermediate mass star is the "black dwarf" phase in which it becomes too faint to even see (Green, 2005, p. 7).
The life cycle of a star is greatly affected by its mass. "More massive stars have greater central temperatures and densities and so exhaust their nuclear fuel more rapidly (in spite of the fact that they have more of it) than do lower mass stars" (Lochner, 2004, p. 3). Simply put, "the larger a star is, the shorter its life. Of course all things are relative -- stars live for billions of years" (, p.2).
A remarkable...
From the explosions or supernovas of existing stars, new stars can arise. "The dust and debris left behind by novas and supernovas are the building blocks for new stars" (, p.3) The "explosive phase" in which "all elements with atomic weights greater than iron are formed" and "blown out into interstellar space" is "remarkable since in the early Universe there were no elements heavier than helium. The first stars were composed almost entirely of hydrogen and helium and there was no oxygen, nitrogen, iron, or any of the other elements that are necessary for life. These were all produced inside massive stars and were all spread throughout space by such supernovae events. We are made up of material that has been processed at least once inside stars" (Lochner, 2004, p.5).
Like humans, stars have a life cycle and tend to group themselves with other similar beings. Their lives are often turbulent and explosive, and their basic elements become part of a chain of cosmic recycling. When we look up at the stars at night, we might see a little of our own origins amongst the twinkling bodies.
References
Green, P. (2005). "Star." World Book Online reference center. 2005. World Book,
Inc. Accessed 6/6/2006 at http://nasa.gov/worldbook/star_worldbook.html
Lochner, J. (2004). "Stars." NASA Goddard Space Flight Center. Accessed 6/6/2006 at http://imagine.gsfc.nasa.gov/docs/science/know_12/stars.html
How Do Stars Form and Evolve?" (2006). The Science Mission Directorate,
Accessed 6/6/2006 at http://hurricanes.nasa.gov/universe/science/stars.html
