FUSE and the Origins of the Universe

FUSE will measure the abundance of deuterium, or "heavy hydrogen," in a variety of astrophysical environments, from local gas clouds to distant clouds along the lines of sight toward quasars and active galactic nuclei. The measurements will determine the extent to which stellar processing has modified the primordial abundance of deuterium, thereby providing a better understanding of the amount produced in the Big Bang and the subsequent chemical evolution of the universe. This provides a direct means for estimating the "baryonic" (or normal matter) content of the universe.

FUSE and the Interstellar Medium

The vast regions between the stars, collectively known as the interstellar medium (or ISM), are not entirely empty, but contain small amounts of gas and dust. These regions can be studied indirectly by the absorption they cause in the light coming from distant stars and galaxies. We know that there are hot and cold regions in the ISM, but the distribution of these regions throughout the Milky Way and in nearby galaxies known as the Magellanic Clouds are only poorly known. The far-UV contains a number of key absorption features from the ISM, which makes FUSE an ideal instrument for studying these exceedingly tenuous regions.

These studies will require observations of many stars and objects at many distances and along many lines of sight to piece together an overall picture of the ISM. In the process of doing this, the FUSE spectra of the objects being used as "background" sources will also provide a wealth of information about objects themselves!