Next Next Previous Previous

Compact Cosmos

19 18 From humble cold clouds of interstellar gas,slowly coalescing under gravity into protostars,stars evolve in a number of ways depending on mass. Theirs is a balancing act between gravity pulling inward and thermonuclear reactions pushing outward. For protostars with a third of the suns mass,gravity squeezes the core to a temperature high enough for nuclear fusion to convert hydrogen into helium. These red dwarfs use their fuel frugally, shining for hundreds of billions of years before fizzling out into a black dwarf. Protostars of less than a tenth of a solar mass skulk about as brown dwarfs,where fusion cant even start. Midmass stars like the sun take a different path. When their fuel is used, the core collapses. Atoms squish together, boosting tem peratures. The outer hydrogen shell ignites, puffing out into a red giant,and the by now helium core starts fusing into carbon. Finally the helium is gone and the core collapses again,but lacking enough mass to generate sufficient heat to further convert the carbon the star fades into a hot,compact white dwarf. Stars of three solar masses or more lead fast,furious lives,rapidly passing through the early stages. Depending on mass, carbon goes on to fuse into neon, then oxygen, silicon, and finally iron when fusion stalls, requiring energy input to continue. During these processes the star swells into asupergiant,hundreds of times the suns diameter. Alas when fusion stops, gravity takes over and the core collapses,culminating in a vast,ironrich explosive supernova,which also forges many other heavy elements. THEMAINSEQUENCE growing up, on and off
From Other Books..
Currently Browsing:
Buy and download E-Book PDF
Buy Softback from Amazon
Buy Hardback from Amazon
Keywords on this page
Show fewer keywords
Show more keywords
See Also:
Log In
Authors List
Series Titles
Special Offers
Powered by Ergonet BookBrowser Engine