Constellation X-Ray Observatory
The Life cycles of Matter and Energy in the Universe
The Universe as an ecosystem: Much like biologists, astronomers trace the flow of matter and energy from one form to another in order to understand the dynamics of the entire system and how it evolves. (Credit: L. Whitlock (GSFC))
Another goal of the Constellation-X mission is to understand how the elements made in stars are dispersed and recycled throughout the Universe, particularly through a supernova, an explosion that marks the end of a massive star's life.
The supernova Cassiopeia A is located in the constellation Cassiopeia 10,000 light years away. This Chandra X-ray image shows the debris of a gigantic stellar explosion. (Credit: NASA/CXC/SAO)
Supernova explosions are one of the most powerful forces in the Universe. A supernova explosion releases more energy than our Sun does over 100 million years. The ultrahigh temperatures generated by supernova explosions can fuse the mid-size elements made in stars (carbon, iron) into heavier ones (gold, uranium). All elements heavier than iron are created in this explosion process. Shock waves from these explosions send the elements made in stars racing into space, often to be recycled billions of miles from their origin. The elements that make up our bodies, in fact, came from an exploded star dispersed by a distant supernova explosion.
The material from the outer layers of a star blown into space by the explosion forms the supernova remnant. This afterglow can be seen for tens of thousands of years. With X-ray spectra from Constellation-X, we will be able to precisely determine the amounts of elements created and dispersed by the supernova.
Chandra and another current X-ray mission, XMM-Newton, have confi rmed theories of how stars produce the most abundant elements and have mapped supernova remnants with great accuracy. Constellation-X will revolutionize this research area with an ability to make extremely sensitive maps of known supernova and observe X rays from sources 100 times fainter than any other X-ray mission could detect. We will be able to construct a full map of the explosion scene by measuring even the least abundant elements. The Universe is the ultimate recycling machine, and understanding this process will be yet one more tool in understanding the Universe's structure and evolution.
Chandra observations of the neutron star RX J1856.5-3754 (left) and the pulsar in 3C58 (right) hint that the matter in these collapsed stars is even denser than nuclear matter, the most dense matter found on Earth. The observations suggest that these stars may be composed of exotic quarks rather than neutrons. (Credit: NASA/SAO/CXC/J. Drake (RX J1856.5-3754), NASA/SAO/CXC/P. Slane (3C58))
Constellation-X might also lead scientists to new types of matter and forces, such as exotic quarks and gluons that could exist in the center of neutron stars. Neutron stars represent another endpoint in the life cycle of a star. While the cores of stars at least 10 times more massive than the Sun ultimately collapse into black holes, slightly less massive stars form neutron stars. These objects contain the mass of about 1.4 suns compacted into a sphere only about 10 miles in diameter. At such density, all the space is squeezed out of the atoms inside the neutron star, and protons and electrons squeeze into neutrons, leaving a neutron superfl uid. The tiny white dot in the center of the image of Cassiopeia A (preceding page) might be the light from a neutron star.
To understand what is inside a neutron star, which scientists call "the equation of state," they need to measure its density. This is a ratio between its mass and radius, a tricky measure to come by. Constellation-X could make this measurement by observing explosions that occur on the surface of neutron stars, bright in X rays. If the neutron star is dense enough, then the neutron core itself might be squeezed to liberate the quarks and gluons that make up all ordinary matter. Such "free" quarks and gluons are only known to have existed at the moment of the Big Bang. The current generation of Xray telescopes provides tantalizing evidence of the existence of these stars, a possible stepping-stone between neutron stars and black holes.
This illustration shows the relative sizes of the Grand Canyon, a neutron star and a quark star. The Grand Canyon is 18 miles rim to rim. A neutron star is about 12 miles across, and a quark star is about 7 miles across. (Credit: CXC/D. Berry)
