September 22, 2006

Astronomers Watch as Stars Are Born

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“We are stardust, billion-year-old carbon,” sang Joni Mitchell. Many artists have been inspired by the idea that since we are made of elements heavier than lithium, we are composed of atoms forged in stars, and any element heavier than iron must have been formed in a supernova. Supernovae are the death throes of stars and release tremendous amounts of energy, enough energy to bind lighter elements together, creating all the heavy elements like gold, platinum and uranium. Since Earth contains plenty of these elements, it has been assumed that the sun is not a first generation star and the solar system must have formed later in order to accumulate all the heavy elements we see on the earth.
Supernovae may even play a more important role that previously thought. Besides providing precious metals, a supernova may have played an integral part in the creation of our sun.
Prof. Lee Hartman, astronomy, University of Michigan, spoke yesterday at the astronomy colloquium about a new, more fast-paced solar creation process. Supported by observational evidence from star forming regions across the galaxy and theoretical models back here on Earth, Hartman presented a plan of solar formation that explains some of the sore points in previous models.
Almost all models begin with a large cloud of hydrogen gas, which astronomers see throughout the galaxy. Gravity from the center of the cloud would pull on the edges and drag the cloud inward. Already there is a problem; if the cloud is allowed to shrink itself completely, it would form far too massive a star at the center. The star would be larger than anything seen in the galaxy today. One hypothesis says that magnetic fields create turbulence that “fluff” the gas, preventing all of it from falling inward.
Hartman disagreed with this hypothesis. The previous theory suggests that star formation occurs slowly and at speeds dictated by the magnetic turbulence rather than by the freefall associated with gravity. However, Hartman suggests that gravity was in charge and inside a large gas cloud the densest regions quickly begin falling inward immediately. Soon these regions are massive enough to be considered stars and begin fusing hydrogen at their cores.
The biggest stars are the first to go, dying because of their own giganticness. As they implode at the center, huge amounts of energy are given off as a supernova. This supernova pushes all the gas in the surrounding region outward in a giant bubble or column. These are often the most striking pictures seen by the Hubble and other telescopes. It is on the edge of these bubbles where gas again becomes dense enough to form stars, except now that the cloud has been spread out over a surface, it no longer will collapse into a single point but into many stars, one of which, we may call home.