Science on the Edge

The James Webb Space Telescope promises to open up new horizons as we gaze to the edges of the visible universe. Webb is an infrared telescope, seeing in a wavelength of light difficult to observe from Earth. Its launch will make the invisible visible and eliminate the haze around some of the most pressing questions of astronomy.

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.

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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.

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First Light

What is reionization?

Shortly after the Big Bang, our universe was filled with a glowing plasma, or ionized gas, of hydrogen and helium.

Scientists think that as the universe cooled and expanded, electrons and protons began to bind together to form hydrogen atoms. The last of the light from the Big Bang faded, and the universe entered an era astronomers call the “Dark Ages.” It's a name that reflects both the time period's main characteristic and the little we know about it.

It would have been a time of absolute darkness, except for the fading infrared glow of the Big Bang. The entire universe would have been full of an opaque fog of gas. Hundreds of millions of years later, some of that fog began to coalesce into dense clumps that would become stars and eventually galaxies. Small patches of light would have burned away at the murk, but without much effect. The hydrogen atoms would have absorbed whatever energetic radiation came their way, extinguishing any glow.

Eventually, though, as the early stars and quasars — incredibly bright objects powered by supermassive black holes — grew in numbers and strength, they would have emitted enough ultraviolet radiation to “reionize” the hydrogen, or turn it back into protons and electrons. Light, no longer devoured by hydrogen atoms, would have spread throughout the universe, revealing the stars and galaxies scattered throughout space, illuminating the cosmos.

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.

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Assembly of Galaxies

Galaxies are where the action is. They're where most star birth, life, and death takes place, along with the related activities we find so important: the production of heavy elements, the formation of planets, and, eventually, the emergence of life.

The Webb telescope is designed to study the small groups of stars that make up the early building blocks of today's galaxies. It will learn when galaxies first appeared, and about the environment they faced. It will analyze the heavy elements produced, and examine the exchange of material between galaxies and the gas, dust, and space between galaxies.Webb will help scientists test the theory that small galaxies cluster together and merge to form larger galaxies. It will investigate the relationship between the evolution of galaxies and the development of the huge black holes at their centers.

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Birth of Stars and Protoplanetary Systems

Stars and planets form together from clouds of gas and dust. Portions of these clouds collapse under their own gravity into denser and denser clumps to create the cores of these just-forming stars. A small amount of this dust and gas remains free of the stars and coalesces into flattened disks around the young stars. Within a few million years, this disk material collects into large bodies and clumps of debris, slowly transforming into gas giant and rocky planets -- perhaps like those in our own solar system.

Webb will probe deep into the dust that surrounds and obscures young stars. Webb can explore the structure of this material to determine the conditions in the disk at the time of planet formation. Exploring these “circumstellar disks” can reveal their interior workings, a complex, evolving structure of shock waves, icy mantles, and dusty collisions. These observations will help unravel the questions that surround the birth and early evolution of stars and the origins of planets, including the mysteries of the earliest bodies in our own solar system.

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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.

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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.

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