The Science Behind DRAGON:
The Origin of the chemical elements, stellar evolution and star death
|Without the elements, we would be nothing. Whether it be the oxygen we breathe, the carbon in our bones, or the gold in our precious jewelry, elements make up every part of our world. But where did these elements come from? When the universe began, the only matter that existed was hydrogen, the smallest of the elements. Since the universe was still fairly hot at this time, some hydrogen was able to fuse (or 'burn') into helium and small quantities of heavier atoms. Still, these processes do not account for the majority of elements we encounter in our day to day lives.|
|To discover where the rest of the elements came from, we must look to the heavens. As the universe cooled, the only place where temperatures were high enough for fusion to occur were the high pressure centers of stars. Less massive stars, like our sun, primarily burn their hydrogen fuel through a cycle known as the proton-proton-chain to produce helium. If carbon is present, they can also burn their fuel through the CNO-cycle (CNO stands for Carbon,Nitrogen and Oxygen). This cycle creates some of the slightly heavier element such as nitrogen and oxygen, but the end result is still helium.|
|Once the hydrogen supply in the core of these stars is depleted, the star will begin to collapse. When the star becomes hot enough, helium will then start to burn into carbon. When the supply of helium is depleted, the carbon will then start to burn, and so forth. Eventually, the star will expell its outer gas layers into space, leaving behind a core of carbon. These events do not account the carbon found in our world, however. The carbon created by these stars is left trapped in a stellar remnant known as a white dwarf. The carbon we're familiar with has a much more explosive background.|
|Most of the heavy elements found on the Earth were created in explosive stellar events known as novae, supernovae, and x-ray bursts. These events happen through the death of massive stars, or through interactions between red giants and white dwarfs. The heavy elements can be created through one of several different processes. They can be be created through a series of rapid proton captures (the rp-process), a series of rapid neutron captures (the r-process), slow neutron captures (the s-process), or through the alpha capture process (alpha particles are the nuclei of helium). Through these processes, stars are able to produce elements as heavy as iron.|
Explosive envionments at the end of a star's life have very high energies and thus, reactions can happen quite rapidly. This changes the usual cycles for element creation, since it is now possible for radioactive isotopes (radioactive versions of the elements) to be present. The goal of DRAGON is to measure the rates of these particular reactions.
These explosions distribute stellar material throughout the universe. Over time, the elements made their way to the cloud of gas that eventually made up our solar system. As Carl Sagan rightly said, "We are all stardust."
For The Beginner
A Description of the Field of Astrophysics
Wikipedia entry on Astrophysics.
- An Educational Tour of Nuclear Data
- Nuclear Astrophysics
Learn what happens as stars are formed, evolve, then die.
- Classical Novae
- Core Collapse Supernovae
- X-Ray Burster
For The Professional
- The Rapid proton capture (RP)-process
- The Supernova Science Center
- Nuclear Astrophysics Data Homepage
- Reaction Rates for Stellar Nucleosynthesis
- Nuclear Data for Nuclear Astrophysics
- Nuclear Astrophysics Bibliography
Lecture Notes from Summer Nuclear Institute 2002
The topic of this institute was nuclear astrophysics.
- The Joint Institute for Nuclear Astrophysics