The Janes Webb Telescope is improved by two main differences from Hubble. The first is just its size: Hubble is about the size of a school bus, while Webb is more like a tennis court. Webb is the largest telescope NASA has ever attempted to send into space.” But it's not just the overall size of the Janes Webb Telescope that matters. In the case of reflecting telescopes, the key component is the size of its curved mirror. “You can think of a kind of telescope mirror like a light bucket,” says astronomers Straughn. The more light you collect in this bucket, the fainter and farther you can see things in the universe.
Hubble's mirror was an impressive 7,8 feet in diameter. Webb's beautiful gold-coloured mirrors come together at 21,3 feet in diameter. Overall, this is more than six times the light gathering area.
What does this mean in practice? Consider Deep Field, one of Hubble's most famous images. In 1995, scientists tuned Hubble to look at a tiny patch of sky (about the size of a pinhead, held at an arm's length from the viewer) and capture as much light as it could from that spot.
The image that came back was astonishing. Hubble uncovered thousands of galaxies in this tiny patch of sky and helped us fix the number of galaxies thought to exist in the universe.
This photo also revealed the greater power of Hubble. In fact, we can call it a time machine in a sense. In astronomy, the farther away objects are, the older they are (because it takes a long time for light from distant places to reach Earth).
This means that Hubble Deep Field is not just a snapshot of space. It also contains the history of our universe. The galaxies in this image look the same to us as they did billions of years ago.
“What Webb is going to do is take that space and go even further,” explains Casey of UT Austin. “So the small spots of light in the background of the Hubble Deep Field will shine and become more detailed, we can see the spiral arms, we can see the structure, and then we get more spots of light. We will begin to receive even more light from the past. In a sense, we can say that we are actually going back in time with Webb.”
With the Webb Telescope, astronomers like Casey will be able to see so far back that they could potentially detect the first stars and galaxies. Hubble saw light dated about 13,3 million years after the Big Bang, which took about 400 billion years to reach us.
“However, Webb has the ability to take us 250 million years after the Big Bang,” he explains.
Casey, approved for work with the Webb Space Telescope. “It may not sound like a big difference. What is a few hundred million years between friends? In fact, this is the difference between seeing the first stars burning and arriving a little late from the funeral,” he answers with a humorous expression.
Beyond that, there are obstacles even Webb can't see. As the National Science Foundation explains, before the first starlight, the universe was shrouded in "a dense, indistinct fog of primordial gas." No light reaches our telescopes from this period, called the cosmic dark ages.
(There is some background radiation from the Big Bang called the cosmic microwave background, a faint glow that shines at us before the dark ages. But for the most part, the dark ages are just a blank spot in our universe timeline.)
Casey and other astronomers hope Webb will help them understand the end of the dark ages and find out what caused this fog to rise. Scientists suspect that starlight from the earliest galaxies does this.
“If you have a cloud of gas and it encounters energetic light, that energetic light will ionize that gas and separate that cloud,” Casey says. “And if that light has just been turned on, it hits the gas and transforms the entire universe from a truly dark place to a bright one.”