Some have called NASA’s James Webb Space Telescope the “telescope that ate astronomy.” It is the most powerful space telescope ever built and a complex piece of mechanical origami that has pushed the limits of human engineering. On Dec. 18, 2021, after years of delays and billions of dollars in cost overruns, the telescope is scheduled to launch into orbit and usher in the next era of astronomy.
I’m an astronomer with a specialty in observational cosmology—I’ve been studying distant galaxies for 30 years. Some of the biggest unanswered questions about the universe relate to its early years just after the Big Bang. When did the first stars and galaxies form? Which came first, and why? I am incredibly excited that astronomers may soon uncover the story of how galaxies started because James Webb was built specifically to answer these very questions.
The ‘Dark Ages’ of the Universe
Excellent evidence shows that the universe started with an event called the Big Bang 13.8 billion years ago, which left it in an ultra-hot, ultra-dense state. The universe immediately began expanding after the Big Bang, cooling as it did so. One second after the Big Bang, the universe was a hundred trillion miles across with an average temperature of an incredible 18 billion degrees Fahrenheit (10 billion degrees Celsius). Around 400,000 years after the Big Bang, the universe was 10 million light-years across and the temperature had cooled to 5,500 degrees Fahrenheit (3,000 degrees Celsius). If anyone had been there to see it at this point, the universe would have been glowing dull red like a giant heat lamp.
Throughout this time, space was filled with a smooth soup of high energy particles, radiation, hydrogen, and helium. There was no structure. As the expanding universe became bigger and colder, the soup thinned out and everything faded to black. This was the start of what astronomers call the Dark Ages of the universe.
The soup of the Dark Ages was not perfectly uniform and due to gravity, tiny areas of gas began to clump together and become more dense. The smooth universe became lumpy and these small clumps of denser gas were seeds for the eventual formation of stars, galaxies, and everything else in the universe.
Although there was nothing to see, the Dark Ages were an important phase in the evolution of the universe.
Looking for the First light
The Dark Ages ended when gravity formed the first stars and galaxies that eventually began to emit the first light. Although astronomers don’t know when first light happened, the best guess is that it was several hundred million years after the Big Bang. Astronomers also don’t know whether stars or galaxies formed first.
Current theories based on how gravity forms structure in a universe dominated by dark matter suggest that small objects—like stars and star clusters—likely formed first and then later grew into dwarf galaxies and then larger galaxies like the Milky Way. These first stars in the universe were extreme objects compared to stars of today. They were a million times brighter but they lived very short lives. They burned hot and bright and when they died, they left behind black holes up to a hundred times the Sun’s mass, which might have acted as the seeds for galaxy formation.
Astronomers would love to study this fascinating and important era of the universe, but detecting first light is incredibly challenging. Compared today’s massive, bright galaxies, the first objects were very small and due to the constant expansion of the universe, they’re now tens of billions of light-years away from Earth. Also, the earliest stars were surrounded by gas left over from their formation and this gas acted like fog that absorbed most of the light. It took several hundred million years for radiation to blast away the fog. This early light is very faint by the time it gets to Earth.
But this is not the only challenge.
As the universe expands, it continuously stretches the wavelength of light traveling through...