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If the James Webb telescope were ten times more powerful, could we see the beginning of time? – Sam H., age 12, Prosper, Texas
The James Webb Space Telescope, JWST for short, is one of the most advanced telescopes ever built. Planning for JWST began more than 25 years ago and construction efforts spanned more than a decade. It was launched into space on December 25, 2021 and arrived at its final destination within a month: 900,000 kilometers away from Earth. Due to its location in space, it has a relatively unobstructed view of the universe.
The telescope’s design was a global effort, led by NASA, and intended to push the boundaries of astronomical observation with revolutionary technology. The mirror is enormous: about 6.5 meters in diameter. That’s almost three times the size of the Hubble Space Telescope, which was launched in 1990 and is still operational.
It is the mirror of a telescope that allows it to collect light. JWSTs are so large that they can ‘see’ the faintest and most distant galaxies and stars in the universe. The state-of-the-art instruments can reveal information about the composition, temperature and motion of these distant cosmic objects.
As an astrophysicist, I constantly look back in time to see what stars, galaxies, and supermassive black holes looked like when their light began its journey to Earth, and I use that information to better understand their growth and evolution. For me, and for thousands of space scientists, the James Webb Space Telescope is a window into that unknown universe.
How far back can JWST see into the cosmos and into the past? About 13.5 billion years.
Time travel
A telescope does not show stars, galaxies and exoplanets as they are now. Instead, astronomers get a glimpse of what they were like in the past. It takes time for light to travel through space and reach our telescopes. This essentially means that a look into space is also a journey back in time.
This applies even to objects that are quite close to us. The light you see from the Sun left it about 8 minutes and 20 seconds earlier. That’s how long it takes for light to travel from the sun to Earth.
You can calculate this easily. All light – whether it is sunlight, a flashlight or a light bulb in your home – travels at a speed of 186,000 miles (almost 300,000 kilometers) per second. That’s just over 11 million miles (about 18 million kilometers) per minute. The sun is about 93 million miles (150 million kilometers) from Earth. That amounts to approximately 8 minutes and 20 seconds.
But the further away something is, the longer it takes for the light to reach us. That’s why the light we see from Proxima Centauri, the closest star to our Sun, is four years old; that is, it is about 25 trillion miles (about 40 trillion kilometers) from Earth, so light takes just over four years to reach us. Or, as scientists like to say, four light years.
JWST recently observed Earendel, one of the most distant stars ever observed. The light that JWST sees from Earendel is about 12.9 billion years old.
The James Webb Space Telescope looks much further back in time than was previously possible with other telescopes, such as the Hubble Space Telescope. For example, while Hubble can see objects 60,000 times fainter than the human eye, the JWST can see objects nearly nine times fainter than even Hubble.
The big Bang
But is it possible to look back to the beginning of time?
The Big Bang is a term used to define the beginning of our universe as we know it. Scientists think it occurred about 13.8 billion years ago. It is the most widely accepted theory among physicists to explain the history of our universe.
However, the name is a bit misleading, as it suggests that some kind of explosion, like fireworks, created the universe. The Big Bang more accurately represents the appearance of rapidly expanding space everywhere in the universe. The environment immediately after the Big Bang resembled a cosmic fog that covered the universe, making it difficult for light to travel beyond it. Eventually, galaxies, stars and planets began to grow.
That is why this era in the universe is called the ‘cosmic Dark Ages’. As the universe continued to expand, the cosmic fog began to rise and light was eventually able to travel freely through space. In fact, a few satellites have observed the light left behind by the Big Bang, about 380,000 years after it occurred. These telescopes are built to detect the smudged, leftover glow from the Big Bang, whose light can be tracked in the microwave band.
But even 380,000 years after the Big Bang, there were no stars and galaxies. The universe was still a very dark place. The cosmic Dark Ages would not end until a few hundred million years later, when the first stars and galaxies began to form.
The James Webb Space Telescope is not designed to look as far back as the Big Bang, but to see the period when the first objects in the universe began to form and emit light. Before this period, there is little light that the James Webb Space Telescope can observe, given the conditions of the early universe and the lack of galaxies and stars.
Looking back at the time period close to the Big Bang is not simply a matter of having a larger mirror; Astronomers have already done this using other satellites that observe microwave emissions from very shortly after the Big Bang. So the James Webb Space Telescope observing the universe a few hundred million years after the Big Bang is not a limitation of the telescope. That’s actually the mission of the telescope. It is a reflection of where in the universe we expect to see the first light from stars and galaxies.
By studying ancient galaxies, scientists hope to understand the unique conditions of the early universe and gain insight into the processes that helped them flourish. That includes the evolution of supermassive black holes, the life cycle of stars and what exoplanets – worlds outside our solar system – are made of.
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This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Adi Foord, University of Maryland, Baltimore County
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Adi Foord does not work for, consult with, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant relationships beyond their academic appointment.