Hubble captured images of the oldest galaxies that it could see here, but the James Webb Space Telescope allows for much more time travel.
This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.
Chris Impey is University Distinguished Professor of Astronomy at University of Arizona
NASA's James Webb Space Telescope has been called the "telescope which ate astronomy" by some. It is the largest space telescope ever constructed and an intricate piece of mechanical origami, which has pushed human engineering to its limits. After years of delays, billions of dollars of cost overruns, this telescope will launch into orbit on December 18, 2021. It will usher in the next age of astronomy.
I am an astronomer, with a specialization in observational cosmology. For 30 years, I have been studying distant galaxies. The universe's early years after the Big Bang are where many of the most important unanswered questions relate. What year were the first galaxies and stars formed? Which was the first and why? Because James Webb was created specifically to answer these questions, I'm thrilled that astronomers will soon discover the story behind how galaxies began.
The dark ages in the universe
The universe was created by an event known as the Big Bang, 13.8 billion years ago. It left it in an extremely hot, ultra-dense condition. After the Big Bang, the universe expanded immediately and then began to cool. The universe was 100 trillion miles across within a second of the Big Bang. It had an average temperature at 18 billion degrees Fahrenheit (or 10 billion billion degrees Celsius). The universe was 10,000,000 light years across, and the temperature had dropped to 5,500° F (3,000° C) around 400,000 years after its Big Bang. The universe would have looked dull and glowing like a giant heat lamp if anyone was there to witness it.
Space was filled with high-energy particles, radiation, hydrogen, and helium throughout this period. There was no structure. The expanding universe got bigger and colder and the soup became thinner and the entire universe went black. This was the beginning of the "dark age" of the universe, according to astronomers.
Because the soup of the dark ages wasn't perfectly uniform, small areas of gas started to clump together due to gravity and became more dense. This made the universe lumpy, and the small clumps that were denser gas became seeds for the formation of stars, galaxies, and all other things in the universe.
The dark ages, even though there was not much to see, were an important stage in the evolution and development of the universe.
Infrared wavelengths are used to describe light from the early universe. This means that it is longer than red light when it reaches Earth. (Image credit: Inductiveload/NASA via Wikimedia commons, CC BY -SA)
Searching for the first light
When gravity created the first stars and galaxies, the dark ages ended. They then began emitting the first light. Astronomers don't know the exact date, but the best guess is it occurred several hundred million years after Big Bang. Astronomers don't know if stars or galaxies formed the first.
Based on current theories about how gravity creates structure in a universe dominated dark matter, it is believed that small objects such as stars and star clusters formed first, and then grew into dwarf galaxies before becoming larger galaxies such as the Milky Way. These stars were far more extreme than stars today. Although they were brighter than today's stars, their lives were very brief. They were bright and hot, and left behind black holes that could have been a hundred times larger than the sun's mass when they died. This might have served as the seeds of galaxy formation.
Astronomers would love the opportunity to study this important and fascinating era in the universe. However, it is extremely difficult to detect first light. The first objects were much smaller than the bright, massive galaxies we see today. They are also far away from Earth due to the constant expansion. The gas that was left from the formation of the stars was surrounded the stars. This gas behaved like a fog and absorbed most light. Radiation took hundreds of millions of years to clear the fog. This is the beginning of light, which is very faint when it reaches Earth.
This isn't the only problem.
The universe expands continuously, extending the wavelength of light that travels through it. This phenomenon is known as redshift. It shifts light from shorter wavelengths, such as blue or white light, to longer wavelengths such red or infrared. It is similar to the way a car passes you and changes the pitch of its sounds.
The universe's expansion has stretched the light 13 billion years ago from the first star or galaxie that it emitted to Earth by a factor 10 and made it reach any telescope on Earth. It arrives as infrared, which means it has a wavelength that is longer than red light. Infrared light is required to see the first light.
Telescope as time machine
Enter the James Webb Space Telescope
Telescopes can be thought of as time machines. It takes 10,000 years for light to reach Earth from 10,000 light-years distant objects. The further we look back in time, the farther out astronomers can see.
The James Webb Space Telescope was created to find the oldest galaxies within the universe. (Image credit NASA/Desiree Steover, CC BY).
James Webb was designed by engineers to detect faint infrared light from the first stars and galaxies. James Webb is 15 times larger than the Hubble Space Telescope and collects six times as much light. Its sensors are also tuned to be more sensitive to infrared.
One strategy is to look at one area of the sky for as long as you can, trying to collect as much information and light from distant galaxies. This data may help us to determine when and how the dark ages ended. However, there are other important discoveries that can be made. This story could help us understand dark matter, the mysterious substance that accounts for about 80% of all the universe's mass.
James Webb is one of the most difficult missions NASA has ever attempted. It will help us answer some of the most important scientific questions. Astronomers like me are eagerly awaiting the data to begin coming back in 2022.
This article was republished by The Conversation under Creative Commons. You can read the original article.
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