Lifestyles of the Stars
Day begins as
twilight sweeps away the darkness. As the light rises in the east, the
stars that have glittered like jewels during the night begin to disappear.
One by one they yield to the spreading light in the east, until even the
brightest fades away. Suddenly the Sun ascends the horizon and its rays
begin to warm our world once more. The Sun moves across the sky and finally
it sinks below the western horizon now itself yielding to twilight and
then the stars again. As long as the Earth has existed, this has been the
cycle. Our Sun seems just right for us. We know that the Sun is just another
star in our skies, just much closer. How does the Sun compare with these
other stars? What would have happened to Earth if the Sun had been bigger?
Our Sun is actually a very average star. It is about 5 billion years old, halfway through its life. It is an average yellow star and thankfully, quite stable. Many stars are smaller or larger. Many are far more massive and some are far less stable. The universe has variety!
All stars begin more or less the same way. In space there are clouds of gas and dust that contain hydrogen molecules. If the cloud is disturbed by either a passing star or a shock wave from a supernova, the cloud may collapse and contract. As it contracts it heats up and fragments. Eventually the fragments contract to the point where nuclear fusion happens: and a star is born.
Once the star begins nuclear fusion it moves onto what is called the main sequence where it will stay for the stable portion of its life. Depending on the mass of the star, it may stay on the main sequence for millions or billions of years. But when its fuel is exhausted, the star will not be able to withstand its own gravity and the end is near.
For stars, bigger is not better. More massive stars burn their fuel much more rapidly and live a much shorter life. The nuclear fusion begin as combining hydrogen to produce helium. Later the larger stars move on to Carbon, Iron and even heavier elements. For stars more massive than the Sun, the ending is violent.
The Sun, and
stars about the same size and smaller, will end their lives quietly by
cooling down and eventually "turning off." Far into the future, as the
Sun begins to exhaust its fuel supply, it will begin to swell. Eventually
it will cool and shrink and fade to what is known as a white dwarf. Life
on Earth will have had plenty of time to move on to other star systems.
If our Sun had been more massive to start with, things would have been very different. These stars do not measure their lives in billions of years, but in millions. Very massive stars have lifetimes so short life would never have time to evolve into intelligence and spaceflight. These stars go through their fuel very quickly and end their lives in a cataclysmic explosion known as a supernova.
You can go out tonight and see many different types of stars. Around 9PM look in the eastern sky. There is a small group of stars rising called the Pleiades, the seven sisters. These stars are members of a stellar nursery, a place where stars are being born. The bright red star Antares in Scorpius is barely visible low in the west just after sunset. Antares is a red supergiant star, elderly and destined to become a supernova.
Overhead and slightly to the west is the summer triangle, three bright stars that are easy to spot. Vega is the brightest, in the constellation Lyra. It is about 2.5 times more massive than our sun and it is hotter. Vega will only spend about 200 million years on the main sequence as opposed to our Sun's 10 billion. Deneb is a blue supergiant star, 25 times more massive than the sun! Deneb's life is fast and furious, it will only spend about 10 million years on the main sequence!
The stars are
fascinating, they come in many varieties. The Sun is ordinary and average,
but this is an ordinary and average for which we can be greteful!
Copyright © 2001 Kathy A. Miles and Charles F. Peters II