Some have called NASA’s James Webb Space Telescope the “telescope that ate 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 Dec. 25, 2021, after years of delays and billions of dollars in cost overruns, the
telescope was launched into space to usher in the next era of astronomy.
Professor Chris Impey, the author of the article this video was based on, is an astronomer
with a specialty in observational cosmology – he's been studying distant galaxies for
30 years.
Some of the biggest unanswered questions about the universe relate to its early years just
after the Big Bang.
When did the first stars and galaxies form?
Which came first, and why?
Professor Impey is incredibly excited that astronomers may soon uncover the story of
how galaxies started because James Webb was built specifically to answer these very questions.
Excellent evidence shows that the universe started with an event called the Big Bang
13.8 billion years ago, which left it in an ultra-hot, ultra-dense state.
The universe immediately began expanding after the Big Bang, cooling as it did so.
One second after the Big Bang, the universe was a hundred trillion miles across with an
average temperature of an incredible 18 billion F (10 billion C).
Around 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 anyone had been there to see it at this point, the universe would have been 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 became bigger and colder, the soup thinned out and everything
faded to black.
This was the start of what astronomers call the Dark Ages of the universe.
The soup of the Dark Ages was not perfectly uniform and due to gravity, tiny areas of
gas began to clump together and become denser.
The smooth universe became lumpy and these small clumps of denser gas were seeds for
the eventual formation of stars, galaxies, and everything else in the universe.
Although there was nothing to see, the Dark Ages were an important phase in the evolution
of the universe.
The Dark Ages ended when gravity formed the first stars and galaxies that eventually began
to emit the first light.
Although astronomers don’t know when the first light happened, the best guess is that
it was several hundred million years after the Big Bang.
Astronomers also don’t know whether stars or galaxies formed first.
Current theories based on how gravity forms structure in a universe dominated by dark
matter suggest that small objects – like stars and star clusters – likely formed
first and then later grew into dwarf galaxies and then larger galaxies like the Milky Way.
These first stars in the universe were extreme objects compared to the stars of today.
They were a million times brighter 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 Sun’s mass, which might have acted as the seeds for galaxy formation.
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 first objects were very small and
due to the constant expansion of the universe, they’re now tens of billions of light-years
away from Earth.
Also, the earliest stars were surrounded by gas left over from their formation and this
gas acted like fog that absorbed most of the light.
It took several hundred million years for radiation to blast away the fog.
This early light is very faint by the time it gets to Earth.
But this is not the only challenge.
As the universe expands, it continuously stretches the wavelength of light traveling through
it.
This is called redshift because it shifts light of shorter wavelengths – like blue
or white light – to longer wavelengths like red or infrared light.
Though not a perfect analogy, it is similar to how when a car drives past you, the pitch
of any sounds it is making drops noticeably.
By the time light emitted by an early star or galaxy 13 billion years ago reaches any
telescope on Earth, it has been stretched by a factor of 10 by the expansion of the
universe.
It arrives as infrared light, meaning it has a wavelength longer than that of red light.
To see the first light, you have to be looking for infrared light.
Enter the James Webb Space Telescope.
Telescopes are like time machines.
If an object is 10,000 light-years away, that means light takes 10,000 years to reach Earth.
So the further out in space astronomers look, the further back in time we are looking.
Engineers optimized James Webb for specifically detecting the faint infrared light of the
earliest stars or galaxies.
Compared to the Hubble Space Telescope, James Webb has a 15 times wider field of view on
its camera, collects six times more light and its sensors are tuned to be most sensitive
to infrared light.
The strategy will be to stare deeply at one patch of sky for a long time, collecting as
much light and information from the most distant and oldest galaxies as possible.
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, unraveling this story may also 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 the scientific questions it may help answer will be worth every ounce of effort.