Hubble took pictures of the oldest galaxies it could ever see, but the James Webb Space Telescope can trace the history of the universe more distantly.
Image credit: nasa
NASA's James Webb Space Telescope has been called the "telescope that ate astronomy." It is the most powerful space telescope ever built and a complex mechanical product that pushes the limits of ergonomics. After years of delays and billions of dollars in cost overruns, the Weber telescope is scheduled to launch into orbit on December 18, 2021, guiding us into the next era of astronomy.
Some of the most significant questions about the universe remain unanswered, and they relate to the early history of the universe after the Big Bang. When did the first stars and galaxies form? Which of them appears first? Why? Astronomers may soon be able to unravel the story of the birth of galaxies, as the James Webb Space Telescope was built specifically to answer these questions, which is exciting.
This diagram shows how the universe has evolved over time. Before stars or galaxies emit any light, the universe went through a period of days known as the "Dark Ages."
Image source: Space telescope institute
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The "dark ages" of the universe
There is ample evidence that the universe began with a Big Bang event 13.8 billion years ago, when it was in an ultra-high, ultra-dense state, and immediately after the Big Bang, the universe began to expand and then cooled down. One second after the Big Bang, the universe was about a million billion miles in diameter and had an average temperature of an incredible 18 billion degrees Fahrenheit (10 billion degrees Celsius); about 400,000 years after the Big Bang, the diameter of the universe became about 10 million light-years, and the temperature also cooled to 5,500 degrees Fahrenheit (3,000 degrees Celsius). If someone were to stand by and look at the universe at this time, it would glow a dark red light like a huge heated lamp.
During this time, space was a chaotic state full of high-energy particles, radiation, hydrogen, and helium, and no structure existed. As it expands, the universe gets bigger and hotter, the "soup" of chaos is diluted, and everything becomes a dull black: the beginning of what astronomers call the universe's "dark ages."
During the "Dark Ages," the universe was not completely homogeneous, and under the influence of gravity, tiny regions of gas began to gather together and become more dense. The smooth universe becomes uneven, and these dense clusters of tiny regions of gas are the seeds that eventually form stars, galaxies, and everything else in the universe.
The universe of the "Dark Ages" saw little substance, but it was an important stage in the evolution of the universe.
This graph shows the size of the object corresponding to the different wavelengths of light, and the light from the early universe reached Earth at infrared wavelengths, that is, light with longer wavelengths than red light.
Look for the first light of the universe
Under gravity, the "dark ages" end when the first stars and galaxies form and eventually emit the first rays of light. Astronomers don't yet know when the first rays of light appeared, but the best guess for observations is hundreds of millions of years after the Big Bang, and it's still an unsolved mystery as to who formed the stars and galaxies first.
Astronomers believe that the universe is dominated by dark matter, and current theories based on how gravity forms structures in the universe suggest that small structures like stars and clusters may form first, which then grow further to form dwarf galaxies, followed by larger galaxies, such as the Milky Way. These original stars in the universe are more extreme than today's stars, millions of times brighter but with a short lifespan; they are hot and bright, leaving behind black holes of up to about 100 times the mass of the Sun after death, and these black holes may be the seeds of galaxy formation.
Astronomers would love to study this fascinating and important cosmic period, but the detection of the first rays of light was extremely challenging. Everything was initially very small compared to today's massive and bright galaxies, and because the universe is expanding, they are now located somewhere tens of billions of light-years away from Earth. In addition, the earliest stars were surrounded by the gas they left behind when they formed, which absorbed most of the light like a fog; radiation took hundreds of millions of years to blow the fog away, and this early light signaled extremely weakly when it reached Earth.
But that's not the only challenge.
As the universe continues to expand, it continues to stretch these rays of light that pass through it, causing its wavelengths to grow larger. This phenomenon is called redshift because it turns shorter wavelength light (such as blue or white light) into longer wavelength light (such as red or infrared light).
When the light emitted by an early star or galaxy 13 billion years ago was observed by a telescope on Earth, it had been stretched 10-fold by the expansion of the universe to reach it in the form of infrared light, meaning it had a wavelength longer than red light. To observe the first light in the universe, you must look for infrared signals.
The telescope is like a time machine
We are about to enter the era of the James Webb Space Telescope.
Telescopes are like time machines, and if a celestial body is ten thousand light-years away from us, it means that light needs to travel ten thousand years to reach Earth. Thus, the farther an astronomer observes in space, the longer the history of the observations will be.
The James Webb Space Telescope is designed to probe the oldest galaxies in the universe.
Image credit: NASA/Jet Propulsion Laboratory – Caltech
Engineers optimized the Weber telescope to detect faint infrared light signals from the earliest stars or galaxies. Compared to the Hubble Space Telescope, James Webb's camera has a 15-fold larger field of view, a 6-fold increase in the number of light signals collected, and a sensor that is tuned to be the most sensitive to infrared light.
The observation plan will be for the Webb telescope to gaze at a certain patch of sky for a long time, collecting as much light and information as possible from the most distant and oldest galaxies. With these data, it is possible to answer when and how the "dark ages" ended, and they are expected to make many other important discoveries, for example, unraveling the suspenseful story of the "dark ages" may also help explain the properties of dark matter, a mysterious form of matter that occupies about 80% of the mass of the universe.
The James Webb telescope is one of the most technically difficult mission NASA has ever attempted, and the scientific questions it might help answer are worth every ounce of effort behind it, and astronomers are excitedly waiting, waiting for data to start returning sometime in 2022.
The author is Chris Impey, distinguished professor of astronomy at the University of Arizona.
Reference: https://theconversation.com/the-most-powerful-space-telescope-ever-built-will-look-back-in-time-to-the-dark-ages-of-the-universe-169603