When astronauts pay a final visit to the Hubble Space Telescope next week, one upgrade in particular will illuminate the darkness like never before -- and it involves taking out the corrective lenses that let Hubble see clearly for the past decade and a half.
The Cosmic Origins Spectrograph, a fridge-sized instrument that will be installed in place of Hubble's original corrective optics set, will help astronomers learn more about the large-scale structure of the universe. Scientists hope it will help explain how stars and galaxies evolved; how the building blocks of life, like carbon and iron, came to be; how matter is distributed in the universe; and, well, what the matter is.
Spacewalking astronauts will also install a new, improved camera, which will continue snapping cosmic postcards for another five years. But with COS, Hubble's next phase will focus on the science of the unseen, to help astronomers better understand the dark materials the pictures can't capture.
"All the things that you make planets and life out of, those were made inside stars somewhere, so if they are out in intergalactic space, presumably they got blown out there, got blasted out there by the stars," said Michael Shull, an astrophysics professor at the University of Colorado and a member of the COS team. "That's one of the forefront issues -- not only how much matter there is, but what it is."
Spectrographs break down light waves into their constituent colors, the way raindrops separate sunlight into a rainbow. Any object that emits or absorbs light can be studied with a spectrograph. By examining spectra, scientists can figure out what makes up the light they're seeing. The gravity of cold dark matter, which we can neither see nor fully understand, pulls regular matter into what's known as the cosmic web, filaments of intergalactic gas separated by huge voids.
The COS will use quasars, which are distant, star-like objects, as lighthouses sending faint signals through that web. Some of the quasars' light is absorbed by the material in the web, and if scientists can determine which parts of light were soaked up, they can figure out the structure of whatever absorbed it.
"At every point, when the light from a distant object cuts through one of those filaments of dark matter, we're going to pick up the missing ordinary matter -- hydrogen, helium, oxygen, all the heavy elements, and we're going to figure out what (the obscured matter) is made of," Shull said. "By looking very carefully, we'll be able to see these little wispy filaments that no one has ever seen before."
He compared the process to a CT scan, in which several images are combined to produce a picture of the entire human body's structure.
"Every spectrum pierces the cosmic web at a different angle. If you get a number of them, you can piece together what it looks like," he said. "Our search is for the intergalactic medium. It's moved beyond 'where is the missing matter?' We want to figure out, what is it made of, and how did it get there?"