Science Goals
Life Cycles of Matter in the Universe
X-ray Images of Supernova Remnants
So, your community just started recycling this year? Well, recycling in the Universe has been the law since the beginning of time. Everything is used again and again, and nothing goes to waste. Sounds economical, doesn't it?
The truth is, the Universe has no giant trashcan. Matter and energy are constantly interchanged. Take our own galaxy, the Milky Way, for example. It contains millions of stars. Like everything else, stars get old and worn out. Some of them turn themselves off quietly with no fanfare and simply go dark. Others end their lives with a spectacular BANG called a supernova explosion. Hydrogen gas released in the explosion can be recycled in the formation of new stars. Heavier elements, such as carbon and iron, can eventually form planets. The iron in our blood and all elements we see on Earth came from stars that exploded long ago.
A star itself is a recycling maniac. Over a course of millions to billions of years, a star will use up all its hydrogen fuel. A star burns hydrogen in a process called nuclear fusion and produces heat. Our Sun is burning hydrogen right now. The spent hydrogen fuel turns to helium. As the hydrogen supply dwindles, the sun starts burning helium. The spent helium fuel turns to carbon. When all the helium is gone, the star starts burning carbon. Then nitrogen. Then oxygen. You get the idea. This recycling process is especially true for stars larger than our Sun. At a certain point, the star may be burning different gases in different shells. It all comes to an end, though, with iron.
Iron cannot burn in a nuclear fusion reaction. When the core of a star is all iron and has nothing left to burn, it can no longer produce energy. Without the energy to support its outer shells, the star collapses then explodes. It takes only a few seconds for a huge star to explode. The supernova then releases a tremendous amount of matter and energy into space -- more energy than our Sun will release in a 100 million years.
In some explosions, a black hole or a neutron star emerges from the fiery remnant. Other times, nothing exotic emerges. The matter ejected from the star simply expands on and on filling the vast and empty space. Forever the spendthrift, the Universe uses this matter. The young are resurrected from the dead! The flesh of the old stars serves as the foundation for the birth of a new generation of stars. And heavy elements such as gold and silver somehow end up in Alaska.
The Universe as an Ecosystem
How do we go about documenting the history of the formation and demise of entities in the Universe? Who fathered whom? Scientists look for clues by tracing the abundances of chemicals in supernova remnants, in galaxies, and in the spaces between stars and galaxies.
The Big Bang made hydrogen, helium, and a tiny bit of lithium. Stars make helium, carbon, and other element in the periodic table as heavy as iron. Star explosions make all the elements heavier than iron. You have the facts; now let's follow with little cosmic logic: Older generation stars do not contain any heavy elements because, although old, they haven't exploded yet. Younger generation stars, born from the remnants of older stars, are enriched with a lot of heavy elements still milling around in the interstellar space. The type and abundance of each element depends on the original progenitor star and the type of explosion it went through. Working backwards, scientists can piece together where the younger stars came from. Working forward, they can tell what will happen to the older stars.
Enter Constellation-X, the magnifying glass of the Sherlock Holmes astronomers. Constellation-X will have both high spectral resolution and high throughput. High spectral resolution allows accurate measurement of the elements dispersed by star explosions. High throughput means Constellation-X has a large collecting area combined with the ability to measure most of the X-rays that reach the detector, an efficiency crucial for analyzing faint and distant X-ray sources. This will enable scientists to determine star, galaxy, and cluster abundances with unprecedented accuracy.
By measuring chemical abundances in these systems over cosmic time, we can record the history of the Universe, the story of how and where we came from. But that's not all we learn. By measuring how the production of elements evolves over cosmic time, we can build physical models of how we expect the Universe to evolve in the future. Thus, we can predict our destiny.
However the future unfolds, you can be sure that there will be a whole lot of recycling going on.
