A million miles from Earth, the James Webb Space Telescope will soar through a frigid void, peering back to the time when new stars and developing galaxies first began to illuminate the universe. Scanning the universe for the invisible radiation called infrared, Webb will have to be larger than any space telescope ever placed in orbit, and function at temperatures just tens of degrees above absolute zero — the temperature at which even atoms are frozen into immobility.
With its infrared vision, Webb will be able to see light from the early universe that has been stretched as it travels across the expanding fabric of space. It will be able to see through clouds of dust to the warm, infrared-emitting objects hidden within. Our view of the universe will expand as Webb opens up previously unexplored territory to our gaze.Back to top
Why an infrared telescope?
Infrared is an invisible wavelength of light beyond the red end of the spectrum. It's invisible to the human eye, but if we can detect it, we gain immensely valuable information about the workings of the universe.
We look for infrared emissions for three reasons. First is the process called “cosmological redshifting.”
The expansion of the universe causes all galaxies to move away from one another, stretching the light from those galaxies as it travels across the universe. As a light wave stretches, it moves toward the red end of the spectrum — thus the name, redshifting.
If an object is extremely far away, the light stretches so much that it moves beyond the end of the visible light spectrum into the invisible infrared. So to see the farthest and earliest galaxies in the universe, we have to be able to look at the light that reaches us in the form of infrared radiation.
Second is infrared's ability to penetrate the dark clouds of dust present in the universe.
Everything gives off some infrared radiation, but warm objects emit large amounts. We see this effect on Earth — night-vision goggles rely on infrared vision to form an image of warm bodies, and certain snakes detect their prey with infrared-sensing organs. Dust clouds block visible light, but not infrared — so by detecting this radiation, we can see through the clouds to the warm objects within.
Third is the simple fact that some things predominantly emit infrared radiation. Not all objects glow with their own light, but even the dimmest objects give off some infrared. Older planets, dust around stars, the early stages of star formation, and clouds of dust drifting in space are all visible in infrared light.Back to top
The universe's first stars, believed to be 30 to 300 times as massive as our Sun and millions of times as bright, would have burned for only a few million years before dying in tremendous explosions, or “supernovae.” These explosions spewed the recently cooked chemical elements of stars outward into the universe before the expiring stars collapsed into black holes or were destroyed.
Scientists suspect the newborn black holes devoured gas and stars around them, becoming the extremely bright objects called “mini-quasars.” The mini-quasars in turn may have grown and merged to become the huge black holes found in the centers of galaxies. Webb will try to find and understand these supernovae and mini-quasars to put theories of early universe formation to the test.
Scientists know that several million years after the Big Bang, the gas in the expanding universe became extremely cold. Gas made up of hydrogen atoms and molecules turned opaque to ultraviolet light. They also know, from viewing distant quasars, that about a billion years later the gas became transparent again. For such a major change to have taken place, the hydrogen must have been reheated by a huge release of energy. Webb will help establish when this reheating, or reionization, happened, and identify the sources of the reheating.Back to top
Assembly of Galaxies
Birth of Stars and Protoplanetary Systems
Planetary Systems and the Origins of Life
Planets exist outside of our solar system, orbiting distant stars. And if other planets exist, could life have taken hold elsewhere in the universe? Learning about the formation and evolution of planets — including our own — will help us understand whether other stars could develop life-bearing planets.
Webb will study the formation of giant planets and “brown dwarfs,” dim objects much smaller than ordinary stars. Giant planets, like our own Jupiter, may indicate a process that could also create Earth-like planets; brown dwarfs, because of the conditions required for their formation, indicate systems in which Earth-like planets would be rare or impossible. Webb will try to determine how common giant planets are and how their formation might affect the creation of terrestrial planets.
Scientists believe that the disks of dust and debris found circling certain stars may be the beginnings of new solar systems. Webb will study these circumstellar disks to look for similarities and differences between their composition and the materials in our own solar system.
Today's telescopes can find planets by watching the changes in the light of a star that occur as a planet passes in front of it. Webb will be able to determine the sizes of the planets, and even the composition of their atmospheres.
Webb will also closely examine comets, which are made of the material left over from the formation of the planets. Scientists can compare the make-up of comets with planet- and star-forming dust and debris, learning how planets form and evolve. Comets are also suspected of being the source of the Earth's water, seeding the planet with water vapor through millions of impacts over billions of years. Webb will help confirm or dismiss this theory by examining comets' composition.Back to top
Future, Unknown Science
When scientists sent Hubble into space, they never expected to find that the expansion of the universe was speeding up. Theory said it should be slowing down. Nor did they realize they'd obtained front-seat tickets to watch a comet crash into Jupiter.
Webb's true value will be known only after it reaches its place among the stars. The greatest science it reveals may be the questions no one has thought to ask yet, the discoveries so unknown, so unexpected, that they open new realms of thought, new floods of questions. Tomorrow's astronomers will have an unprecedented tool at their disposal to explore the cosmos. Webb's greatest science may very well lie in areas that have yet even to be imagined.Back to top