Lifestyles of the Stars

Lifestyles of the Stars

As you gaze up into the star filled night you might not give much thought to the idea that stars don't last forever. You may know that they are a huge ball of burning gas, but they also have a "lifestyle" that they follow according to their size. And if you look around the area of sky occupied by Orion and the surrounding constellations, you'll get to see a pretty wide range to the phases a
star passes through.

Stars begin in stellar "nurseries," huge wispy clouds of gas and dust which lurks in the vacuum of space between stars. The cloud is made up of about 75 percent hydrogen, 25 percent helium and trace amounts of carbon, nitrogen, oxygen, calcium, sodium and heavier atoms. About 1 percent ot the cloud is made up of dust particles the size of the particles in cigarette smoke. The dust is probably carbon, iron and ice coated silicates.

For stars to actually form from these clouds a number of things must happen. First, the cloud must be sufficiently dense enough to make it contract some. Gravity will tend to pull all the atoms toward the center of the cloud. Now what is needed is something to cause a bit of instability, something which will make the clouds collapse inward under the influence of gravity. Astronomers believe that this can happen a number of ways. One way is for a shock wave to hit the cloud and compress it. Fortunately space is filled with such shock waves caused by nova, stars which end in a tremendous explosion. Another thing which causes stars to form is shock waves from other stars "turning on." But the main cause of star formation is the rotation of the galaxy itself. As the stars rotate around the center of the galaxy they pass through interstellar clouds and cause shock waves which in turn cause the clouds to collapse and form stars.

These stellar nurseries are all over the galaxy. One of the most obvious is in the constellation
Orion. You will need a pair of binoculars to see this but it is worth looking at. Find the three stars which make up the belt of Orion. Follow the middle belt star downward and you may see a faint smudgy patch. Binoculars will reveal a massive cloud where stars are being born.

What makes a star a star? Basically they are a huge ball of burning gas. They create energy by nuclear reactions. The most common reaction is to fuse hydrogen into helium. Once the star begins to do these reactions it is said to enter the "main sequence" of stellar evolution, where it will spend the majority of its time. Very massive stars are much hotter and can fuse heavier elements in reactions, such as Carbon.

To look at a slightly older group of stars, look to the west of Orion. You'll see a small compact group of stars called the Pleiades, or seven sisters. They are part of the constellation Taurus the Bull. These are hot, young, blue stars all traveling together as a group. Binoculars will reveal some gas around the young stars.

Now look nearly overhead and you will see a yellowish star called Capella in the constellation Auriga the Charioteer. This star is a middle aged yellow star, much like our star, the Sun. It is actually a multiple star system and binoculars will reveal one of Capella's companions. Many stars are double and multiple systems. Some only appear double due to line of sight, while other stars actually revolve around each other and form a physical pair bound by gravity.

There are a number of good examples of stars in the senior age status. Stars can meet their ends in a few different ways all of which depend on one thing, their mass. The more massive a star, the faster it evolves. Star's "life spans" range from a few hundred million years to many billions of years.

Stars which are about half the size of the Sun burn up their hydrogen and then slowly cool down. These stars are not hot enough to burn anything other than hydrogen. Stars up to about 3 times the mass of the Sun have a similar ending but often blow off part of themselves to form a nebula around the central star. They they follow the path of the smaller stars and end up as cool stars called white dwarfs. These stars are hard to see, because they are not very bright and are quite small. They are however, very dense. A piece of white dwarf the size of a tennis ball would weigh more than 2 full grown elephants!

It is the very massive stars which have spectacular violent endings. These stars fuse nuclear fuels all the way up to iron! When an iron core forms in a massive star, the core collapses and triggers an explosion called a supernova. A good example of a very massive star which will have this fate (and soon, by astronomical standards!) is Betelguese, the upper left star in Orion.

Betelguese is an enormous star. If it were placed in the center of our solar system, this massive supergiant would extend out beyond the orbit of Jupiter! The lifespan of a star as large as Betelguese is only 4 to 10 million years!

Supernova explosions are the universe's form of urban renewal. They create heavier elements than iron, such as gold. All gold (and any element heavier than iron) originated from a supernova explosion somewhere in the galaxy! You may very likely have some "star stuff" within your body!