The Webb Space Telescope is built with some of the most sophisticated scientific instruments sent beyond Earth’s orbit. Astronomers hope the spacecraft will help them understand more about black holes, how stars are born and die, and what’s in the atmospheres of planets orbiting other stars. Perhaps, it will even give us a glimpse of an epoch close to the Big Bang.
Why does looking further help scientists see past billions of years?
Remember the speed of light? A constant speed through the vacuum of space is 186,000 miles per second, or over six trillion miles per year.
This makes a light year – the distance light travels in one year – a handy measuring stick for cosmic distances.
It also explains why looking into the universe is looking into the past.
If a star is 10 light-years away, it means that its light took 10 years to reach us: we are observing a star that was 10 years ago. (Light from the Sun takes eight minutes to reach the Earth.)
For the most distant objects that the Web can detect, those particles of light travel about 13 billion light-years, traveling through space for 13 billion years. The light in the Web “Deep Field” image released Monday is a snapshot of a region of the universe that is less than a billion years old.
What can learning more about the period close to the Big Bang teach astronomers?
When did the first stars shine? When did the first galaxies coalesce from gas clouds? How different were the first stars and galaxies that fill the universe today?
Nobody really knows. It is a missing chapter in the history of the universe. We know that the universe began in an instant from the Big Bang. That explosion left a wake of microwave noise that was discovered in 1964 and has been studied extensively over the decades. The universe cooled, matter began to accumulate and the first stars are thought to have formed about 100 million years after the Big Bang.
The early stars must have been different because the Big Bang produced only hydrogen and helium along with lithium and beryllium. Heavy elements – carbon, silicon, iron and none of the rest of the periodic table. Some astrophysicists believe that many of the first stars, devoid of heavy elements, were massive, burned brightly and died young in supernova explosions, scattering material that could later form planets and eventually life like us.
Webb is the first telescope to detect and analyze those early stars.
Why do Webb’s tools help advance this work?
The two main differences between Webb and Hubble are the size of their mirrors—larger mirrors collect more light—and the wavelengths of light they observe. Hubble focuses on visible and ultraviolet wavelengths, providing unparalleled new views of much of the universe.
But for the early universe, the infrared part of the spectrum was important. That’s because of the Doppler effect. When a police car is speeding, the pitch of the siren is higher as the car approaches and lower as it speeds away. Basically the same thing happens with light. Objects speeding toward us appear blue, and those receding appear red because the receding motion stretches the wavelengths of the light particles outside. For very distant objects, such as early stars and galaxies, most of the light is shifted to the infrared.
Infrared observations from telescopes on Earth are essentially impossible. The atmosphere blocks those wavelengths.
Infrared observations can be easily corrupted by thermal radiation. That’s why the web was placed a million miles from Earth and shadowed by a giant solar shield. One of the instruments, the Mid-Infrared Instrument, or MIRI, must be cooled to minus 447 degrees Fahrenheit to function properly.
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