Much of the process of stellar creation is supposition; however, observations tend to support the way that many scientists believe that a star forms. The Hubble and other space telescopes have also given stunning pictures and data of regions where star formation is going on, further supporting what is believed to be the cause and the sequence of events.
Gas and dust
The process begins with tenuous clouds of gas, mostly hydrogen, and dust. The clouds are vast, particularly in stellar nurseries in which they might span many light-years to thousands of light-years. A light-year is the distance light travels in a year, just under 6 trillion miles. Though the gas and dust show up well in photographic images taken by Hubble and other telescopes, most of each cloud is empty space. Because of this, the clouds have enough matter to produce many stars the size of our sun; however, the gravitational pull isn’t usually strong enough to pull the particles together.
For reasons not clearly understood, an event causes the clouds to begin condensing. Some have hypothesized that this is caused by compression waves that pass through the cloud, bunching up the material the cloud contains, rather like how a bow wave forms immediately in front of a boat that is moving through water. There are several theories about why the compression waves exist and what causes them, including supernova explosions, causes due to black holes interacting with matter and other possibilities. When the dust and gas are compressed enough that the substances can lump together and the density of the cloud increases, gravitational forces can then begin to take over.
From a humble beginning, the tiny clumps of matter attract yet more gas and dust, causing the mass of the object to gradually increase. The more matter it contains, the more gravitation the nucleus is able to exert. This does more than to make the early protostar larger. It also causes the interior to begin to warm up due to friction, in a way similar to rubbing hands together makes them feel warm, only on a much larger and more intense scale. The mass usually becomes enormous, though. With the increased friction from the large mass, the object continues to become hotter at the center where the gravitational forces are strongest.
When the mass, gravitation and temperature become great enough, hydrogen begins to fuse together, forming helium. The star is “born.” The nuclear reaction creates an enormous outward force and at the point where the outward force balances the gravitation that is still attempting to draw the matter inward, the new star becomes fairly stable.
The amount of mass in the star determines the type of star it is and how hot it is going to be burning. For example, if the mass is about one-sixth that of Earth’s sun Sol, the star is destined to be a red dwarf star, burning at relatively cool temperatures in comparison with the sun, and for an exceptionally long time, perhaps on the order of trillions of years. If the mass is dozens to hundreds of times greater than that of our sun, the star can become a blue super-giant, producing far more radiation than the sun but burning at an accelerated rate so that its lifetime can be measured in the millions of years or even less. The sun is intermediate between the extremes and it is believed that it is roughly halfway through its life, after about five billion years.
The newly created star spins, too, and as it does so, leftover material flattens out into a disk, revolving around the star. This material can lead to planet formation from gravitational forces, similar to those that caused the star to form.
Nova and supernova star explosions at the end of the stars’ lives add more dust and gas to the mix for the next generation of stars to be created. Interestingly, many of the best photographs of stellar creation are of the Large and Small Magellanic clouds, satellite galaxies of the Milky Way. Part of the reason for this is that there is less gas and dust between the earth and these galaxies, making them easier to view.
While there are still some questions that are left unanswered regarding star creation, and though the entire process usually takes a great deal of time, most of the doubts revolve around specific parts of the sequence rather than star formation in general. Man hasn’t been around long enough and doesn’t live enough years to actually witness the process, but so many stars are being formed that the various stages of the creation can be seen. There may still be some other pieces to the puzzle that are waiting to be found, however.