Wednesday, September 28, 2022

The most powerful space telescope ever built will look back in time to the Dark Ages of the universe

Some have called NASA’s James Webb Space Telescope “the telescope that eats away at 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 December 18, 2021, after years of delays and billions of dollars in cost escalation, the telescope is set to be launched into orbit and usher in the next era of astronomy.

I’m an astronomer specializing in observational cosmology – I’ve been studying distant galaxies for over 30 years. Some of the biggest unanswered questions about the universe pertain to the early years just after the Big Bang. When did the first stars and galaxies form? Who came first, and why? I’m incredibly excited that astronomers may soon uncover the story of the beginning of galaxies because James Webb was created specifically to answer these very questions.

The universe passed through a time known as the Dark Ages before stars or galaxies emitted any light.
Chris Impey, CC BY-ND

The ‘dark ages’ of the universe

Excellent evidence shows that the universe began 13.8 billion years ago with an event called the Big Bang, which left it in a super-hot, ultra-dense state. The universe began to expand shortly after the Big Bang, cooling as it did so. One second after the Big Bang, the universe was at a distance of one hundred trillion miles, with an average temperature of an incredible 18 billion F (10 billion C). About 400,000 years after the Big Bang, the universe was 10 million light-years across and the temperature had cooled to 5,500 F (3,000 C). If someone were to observe it at this point, the universe would be 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 got bigger and colder, the soup got thinner and everything darkened. This was the beginning of what astronomers call the Dark Ages of the universe.

The soup of the Dark Ages was not completely uniform and due to gravity, small spheres of gas began to collide and become more dense. The smooth universe became lumpy and these tiny clumps of dense gas were the seeds for the formation of stars, galaxies and everything else in the universe.

Although there was nothing to see, the Dark Ages were an important stage in the evolution of the universe.

A diagram showing different wavelengths of light compared to the size of normal objects.
Light from the early universe is in infrared wavelengths – meaning longer than red light – when it reaches Earth.
Inductive Load/NASA, CC BY-SA via Wikimedia Commons

looking for first light

The Dark Ages ended when gravity created the first stars and galaxies that eventually began to emit the first light. Although astronomers do not know exactly when light first occurred, the best estimate is that it was several hundred million years after the Big Bang. Astronomers don’t even know whether stars or galaxies first formed.

Current theories based on how gravity creates structure in a dark matter-dominated universe suggest that smaller objects – such as stars and star clusters – are likely to first form and then later evolve into dwarf galaxies and then larger galaxies such as the Milky Way. Hui. These first stars in the universe were extreme objects compared to today’s stars. They were a million times faster 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 mass of the Sun, which might have served as seeds for the formation of the Milky Way.

Astronomers would love to study this fascinating and important era of the universe, but detecting first light is incredibly challenging. Compared to the massive, bright galaxies of today, the objects were previously very small and, due to the continual expansion of the universe, they are now tens of billions of light-years away from Earth. In addition, early stars were surrounded by gas left over from their formation and this gas acted as a fog that absorbed most of the light. It took several hundred million years for radiation to clear the fog. This initial light becomes very less by the time it reaches the Earth.

But this is not the only challenge.

As the universe expands, it continuously increases the wavelength of light traveling through it. It is called redshift because it shifts light of shorter wavelengths – such as blue or white light – to longer wavelengths such as red or infrared light. While this is not a complete analogy, it is similar to how the pitch of any sound becomes noticeable when a car passes by you.

Just as the pitch of sound drops as the source is moving away from you, the wavelength of light expands due to the expansion of the universe.

By the time the light emitted by an early star or galaxy 13 billion years ago reaches a telescope on Earth, it has expanded 10 times the expansion of the universe. It comes in the form of infrared light, which means it has a longer wavelength than red light. To see the first light, you have to look for infrared light.

[The Conversation’s science, health and technology editors pick their favorite stories. Weekly on Wednesdays.]

Telescope as Time Machine

Enter the James Webb Space Telescope.

Telescopes are like time machines. If an object is 10,000 light years away, that means it takes 10,000 years for light to reach Earth. So the farther space astronomers look, the farther back we are looking at time.

A large golden disc with the sensor in the middle and the scientist standing below.
The James Webb Space Telescope was specifically designed to detect the oldest galaxies in the universe.
NASA/JPL-Caltech, CC BY-SA

Engineers adapted James Webb specifically to detect the faint infrared light of early stars or galaxies. Compared to the Hubble Space Telescope, James Webb’s camera has a 15 times wider field of view, collects six times more light and its sensors are most sensitive to infrared light.

The strategy would be to stare deeply at a part of the sky for long periods of time, collecting as much light and information as possible from the farthest and oldest galaxies. With this data, it may be possible to answer when and how the Dark Ages ended, but there are many other important discoveries to be made. For example, knowing this story could help explain the nature of dark matter, the mysterious form of matter that makes up about 80% of the mass of the universe.

James Webb is the most technically difficult mission NASA has ever attempted. But I think it will help to answer scientific questions that will be worth every effort. Me and other astronomers are excitedly waiting for the data to come back sometime in 2022.

This article is republished from – The Conversation – Read the – original article.

Nation World News Desk
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