Pat Merwah, age 12, of St. Louis, Missouri, for her question:
How long is the life of a normal star?
Our radiant sun is as normal as a star can be. Its dazzling face has been shining for billions of years. As stars go, it is a young adult with a life expectancy of billions more years of glory. But sometime in the far. distant future, our normal star must grow old and shine no more.
Our Galaxy is populated with about 100 billion assorted stars. The normal stars, of course, are those in the majority but this group includes several widely different types. It ranges from stupendous super giants through a variety of medium sized stars down to planet sized dwarfs. Each type is a seething powerhouse consuming nuclear fuel. It is born when the nuclear furnace is lit and starts to glow. Each type burns up its original hydrogen at a certain rate, faster or slower, and when this nuclear fuel is all used up, the furnace dies.
Astronomers can estimate the life span of a normal star but they cannot state an exact figure within a few million or even a few billion years. Physicists now understand the process of nuclear fission that powers a star and the heavens are strewn with countless starry powerhouses for them to study and compare. When they know how fast a star is burning and how much hydrogen fuel it has left, they can estimate how much longer its blazing furnace can last.
The handiest normal star to study, naturally, is our sun. We know its exact output ot energy and just how fast it is burning. We can estimate its remaining fuel and how long it will last at the present rate. Scientists figure that it can blaze in the same old way for another 10 to 15 billion years. Then the nuclear furnace will be upset by too much ash and too little fuel.
At this point in the distant future, our normal star is expected to erupt in an outburst hot enough to roast its planets. After this fiery flash, its core of ashes will collapse and for perhaps another five billion years, the sun may shine on as a hot little white dwarf star. After a radiant life span of 20 to 30 billion years, it will become a black dwarf a dead, dark ball of cold ashes doomed to roam the Galaxy for all eternity.
The stars are created one by one from gaseous cosmic clouds. New stars are being born in the cloudy regions of the Milky Way, and in regions free of cosmic debris, others are growing old. Many bright, hot stars are burning their fuel fast and will die ages before our sun. Some of the hots red giants may burn for only a million years or less. Many dim stars in the normal group are burning slowly and may outlive the sun by many billions of years.
All life on earth depends on the shining sun, but the sun cannot shine forever. We have perhaps IO billion years to make our plans for moving to another home in the heavens. Luckily, there are many suitable homes in our celestial neighborhood. The best choice would be a gentle, slow burning star with a long, long shining life ahead. No doubt, in the far future, the unbeatable human family will pack up and move, with all its precious belongings to such a durable star and make a new home on one of its planets.