COS is designed to study the large-scale structure of the universe and how galaxies, stars and planets formed and evolved. It will help determine how elements needed for life such as carbon and iron first formed and how their abundances have increased over the lifetime of the universe.
As a spectrograph, COS won’t capture the majestic visual images that Hubble is known for, but rather it will perform spectroscopy, the science of breaking up light into its individual components. Any object that absorbs or emits light can be studied with a spectrograph to determine its temperature, density, chemical composition and velocity.
A primary science objective for COS is to measure the structure and composition of the ordinary matter that is concentrated in what scientists call the ‘cosmic web’—long, narrow filaments of galaxies and intergalactic gas separated by huge voids. The cosmic web is shaped by the gravity of the mysterious, underlying cold dark matter, while ordinary matter serves as a luminous tracery of the filaments. COS will use scores of faint distant quasars as ‘cosmic flashlights,’ whose beams of light have passed through the cosmic web. Absorption of this light by material in the web will reveal the characteristic spectral fingerprints of that material. This will allow Hubble observers to deduce its composition and its specific location in space. See: Hubble Space Telescope Service Mission 4- Cosmic Origins Spectrograph
Cosmic Origins Spectrograph optical path: The FUV and NUV channels initially share a common path. The first optic is either a concave, holographically ruled diffraction grating which directs light to the FUV detector (red) or a concave mirror directing light to the NUV gratings and the NUV detector (purple). The green ray packets represent the FUV optical paths, and blue ray packets represent the NUV optical paths. A wavelength reference and flat field delivery system is shown at top left (orange ray packets) and can provide simultaneous wavelength reference spectra during science observations.