The collision of the Antennae galaxies triggered the formation of millions of stars in clouds of gas and dust within the galaxies. 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.
When we look out into the universe, we see galaxies with magnificent spiraling arms and galaxies that glow like giant lightbulbs. But these spiral and elliptical galaxies weren't born in these familiar shapes. Galaxies in the early universe were probably small and clumpy. So how did these modest groups of stars evolve into the grand structures we see today?
When telescopes peer into the universe, they look 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 it arrives on Earth. The most distant galaxies Hubble has spied are more than 13 billion light-years away. That means the light Hubble captures 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, turning visible light into infrared light. 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. But infrared light will be the Webb telescope's specialty.
Light must travel through space over time. As telescopes capture light emanating from objects in the distant universe, they observe different stages of development. Webb's infrared vision will allow it to see the first stars and galaxies to develop after the Big Bang.
Where Hubble sees young galaxies, Webb will show us newborns. Webb will capture the earliest stages of galaxy formation, and perhaps even reveal when galaxies first started forming in the universe. Webb could show how small galaxies in the early universe merged to form larger galaxies. Finally, Webb will see more of the ordinary early galaxies, where Hubble only sees the brightest outliers. This expanded sample of early galaxies will give astronomers a better idea of how galaxies really looked as they first came into being, and help to map the universe's overall structure.
The Hidden Universe
Webb's infrared prowess will also allow it to see inside dust-cloaked regions of galaxies that visible light cannot escape from, and find out what's happening within them. For many different types and ages of galaxies, Webb will expose how stars are forming, how many stars are forming, and how star formation is affected by the surrounding environment. Webb will study star-birth regions in merging galaxies, revealing how these galactic encounters trigger and alter the course of star formation as their gaseous components collide and mix. Webb will analyze how elements are produced and distributed in galaxies, and also examine the exchange of material between galaxies and the space between them.
Webb will also 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.
Hubble's eXtreme Deep Field image combines a decade of Hubble observations, including some taken in infrared light, to create one of the deepest pictures of the universe ever taken, spanning 13.2 billion years of galaxy formation. About 5,000 galaxies appear in this image.
Eventually the gas would have 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 massive black holes, or some even more exotic source such as decaying dark matter. Webb's infrared capabilities will allow it to identify the sources that gave rise to reionization. And perhaps Webb will see the stars and bright galaxies called "quasars" that unleashed enough energy to re-illuminate the universe.