| While most of us can average a healthy lifespan of 80 to 90 years, our sun's life expectancy eclipses that by a good bit -- most scientists estimate that the sun will continue to burn brightly for another five billion years or so. The sun is our nearest star and while not all stars are alike, their age, and therefore their lifespan, can generally be predicted by theirluminosity and size. Stars fall into size/age categories such as brown dwarfs, white dwarfs, and red giants. While these terms may sound more like the names of fairy-tale characters, they identify the phase of a star's current stage in the process of stellar evolution. A star is born when interstellar gas -- which consists of mostly hydrogen, some helium, and traces of heavier elements -- coalesces to form a big, glowing ball of fire. A brown dwarf is a "failed star" that never attained thermonuclear reaction. A middle-aged star, like our sun, falls into the yellow dwarf category. Put simply, this is when the star's tank is half full. It is also when it shines steadily, converting its hydrogen reserves into helium. As the helium supply within the star�s core burgeons, the core contracts and releases gravitational energy. This activity increases the rates of nuclear reactions, and the star begins to swell dramatically in size. When it reaches this point, the star enters the red giant phase, a signal that it's headed towards early retirement. Eventually the climate of this inflated star gets too hot to handle. Depending on a star's mass, it can either explode in a supernova, or collapse and become a white dwarf. From studying similar stars, astronomers believe our sun will form the latter. After rearranging its internal structure and going through several cycles of expansion and contraction, the sun will eventually form a planetary nebula and just sort of drift apart as the core loses its gravitational hold on the outer layers, leaving behind a cold, dead lump of carbon. More of a whimper than a bang really... |
