How Can Webb Study the Early Universe?

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When astronomers use a telescope to look further away, they are also looking back in time.

The Antennae galaxies
The collision of the Antennae galaxies triggered the formation of millions of stars. Infrared observations in this image show warm dust clouds heated by newborn stars, with the brightest clouds lying in the overlapping region between the galaxies. CREDIT: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration; acknowledgment: B. Whitmore (STScI).

When we look out into the universe, we see a variety of galaxy shapes: some with magnificent spiraling arms, others that appear to glow like giant lightbulbs. These spiral and elliptical galaxies haven’t always had these familiar shapes, though; galaxies in the early universe were probably small, unformed clumps. A big question in astronomy is how these early, modest groupings of stars evolved into the grand structures we see today.

When astronomers use a telescope to look further away, they are also looking back in time. The reason is simple: light needs time to travel through space. Even the light from the Moon is 1.3 seconds old when we see it on Earth. The most distant galaxies the Hubble Space Telescope has viewed are more than 13 billion light-years away. That means the light Hubble captured left those galaxies over 13 billion years ago.

But there’s another complication. As the universe expands, light gets stretched into longer and longer wavelengths, beyond the visible portion of the spectrum, into the infrared. By the time visible light from extremely distant galaxies reaches us, it appears as infrared light. Hubble can detect some infrared light—the wavelengths closest to the red end of the visible spectrum. The James Webb Space Telescope observes infrared wavelengths exclusively, seeing deeper into that portion of the spectrum than Hubble.

Where Hubble sees young galaxies, Webb can show us newborns. Webb is engineered to observe the earliest stages of galaxy formation and astronomers are hopeful it will allow them to study the formation of the very first galaxies. Webb could show how small galaxies in the early universe merged to form larger galaxies. Finally, where Hubble only sees the brightest outliers from this ancient epoch, Webb is capable of revealing much more of the general population of stars and galaxies during that period. This expanded sample of early galaxies will give astronomers a better idea of how galaxies looked as they first came into being and help them map the universe’s overall structure.

The Electromagnetic Spectrum
The light we can see with our eyes represents only a very small portion of the continuous range of electromagnetic waves that form the electromagnetic spectrum. CREDIT: NASA and J. Olmsted (STScI). GET THE FULL IMAGE IN RESOURCE GALLERY >

Where Hubble sees young galaxies, Webb can show us newborns. Webb is engineered to observe the earliest stages of galaxy formation and astronomers are hopeful it will allow them to study the formation of the very first galaxies. Webb could show how small galaxies in the early universe merged to form larger galaxies. Finally, where Hubble only sees the brightest outliers from this ancient epoch, Webb is capable of revealing much more of the general population of stars and galaxies during that period. This expanded sample of early galaxies will give astronomers a better idea of how galaxies looked as they first came into being and help them map the universe’s overall structure.

The Hidden Universe

Hubble's eXtreme Deep Field
Hubble’s eXtreme Deep Field image combines a decade of Hubble observations, including some taken in near-infrared light, to create one of the deepest images of the universe ever assembled, spanning 13.2 billion years of galaxy formation. About 5,000 galaxies appear in this image. CREDIT: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team.

Webb's infrared instruments allow it to see inside regions of galaxies that are obscured by dust when viewed in visible light, illuminating the process and context of star formation. Webb will also study star-birth regions in merging galaxies like the Antennae galaxies (pictured above), revealing how these galactic encounters trigger and alter the course of star formation as their gaseous components collide and mix.

In addition to studying previously shrouded stellar nurseries, astronomers can use Webb to explore an era known as the Dark Ages and the time immediately following it, the period of reionization. About 378,000 years after the Big Bang, as the universe cooled and expanded, electrons and protons began to bind together to form hydrogen atoms. As the last of the light from the Big Bang faded, the universe would have been a dark place, with no sources of light within the cooling hydrogen gas. Eventually, the gas coalesced to form stars and eventually galaxies. Over time, most of the hydrogen was "reionized," turning it back into protons and electrons and allowing light to travel across space once again.

Astronomers are currently unsure whether the energy responsible for reionization came from stars in the early-forming galaxies, hot gas surrounding black holes, or some even more exotic source such as decaying dark matter. Webb's infrared capabilities allow it to identify the sources that gave rise to reionization, and perhaps see the stars and bright galaxies called quasars that unleashed enough energy to re-illuminate the universe.

Last Updated: May 31, 2018

Keywords:  CosmologyUniverse Age/Size

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