In the vast spaces between stars are giant clouds of dust and gas. The gas is mostly hydrogen, the predominant element present when the universe was created. When a cloud of gas is set off by such cosmic forces as shock waves from the supernova death of an old giant star, it can begin condensing by the force of its own gravity (which pulls all matter toward other matter). When that happens it compresses tighter and tighter, depending on how much mass was in the original cloud and how it was clumped. The more the hydrogen atoms are squeezed by the gravitational pull inward, the hotter they get. If there was enough gas in the cloud, gravity continues to pull it together until the pressure and temperature at the core reaches about 10 million degrees Kelvin.At this temperature hydrogen atoms actually begin to fuse together to form heavier helium atoms. Every time four hydrogen atoms fuse to make a helium atom, a sub-atomic particle is left over and released as energy. This is called thermo-nuclear fusion. These particles of energy work their way to the surface and are radiated out into space. When this process begins, a sun has turned on! A star is born!
After thermo-nuclear fusion begins, the continuing gravitational pull inward becomes balanced by the energy being released, which pushes outward. The sun reaches a state of equilibrium. It becomes stabilized in size and will remain that size during most of its "life". Our own sun, which is about 4 1/2 billion years old and about half way through its supply of hydrogen fuel, is in that state of equilibrium.
Millions or billions of years later as the hydrogen becomes used up, the outward energy decreases, and the sun begins to contract further. At some point, so much further heat is created by the further squeezing that helium atoms start fusing into carbon atoms. For a shorter period it stabilizes in size again, but then further contraction again begins as the helium is used up. What happens after that, which ultimately leads to the death of the sun, depends on the amount of mass (matter) in the sun. The different ways that suns die is another fascinating subject, for another time.
Stars frequently form in groups. There are places in the sky where you can see this process occurring. Such places are called nebulae (pronounced NEB-u-lee, plural of nebula). Nebulae are some of the most beautiful objects in space to observe with a pair of binoculars or a telescope.
The most famous and easily seen is "The Great Nebula" in Orion. This nebula is in the "hunter's sword" hanging underneath the three bright stars in a row in the winter sky, that form the famous "belt of Orion" in the Orion Constellation. The "sword" comes down from the left side of the "belt" and appears with the naked eye as a hazy, fuzzy area with three dim stars in it. With binoculars or a small telescope it appears as a glowing cloud with bright stars inside that light it up. On a cosmic time scale, these are baby stars, just born, some of them only a few hundred thousand years old or less The remaining clumps of gas are still contracting to form more stars. This is a stellar nursery, a star cluster in the making, in which a whole litter of stars is being born.
At some time in the future most of the gas in the Orion Nebula will have condensed into suns, and possibly into planets rotating around them. The radiation and energy released by these young hot stars will "blow away" the embryonic remains of gas that surrounds them, leaving a cluster of sparkling new suns.
Back to Star Facts Home Page
Send suggestions, astronomy tips, corrections or comments to Pete Harris
via e-mail at odyssey@ccnet.com. Pete is also the creator of the website
The Child
Abuse Prevention Council of Contra Costa County