How the James Webb Space Telescope sees the universe's first galaxies
Webb looks in infrared, sits 1.5 million kilometres from Earth and keeps its instruments colder than anything around them. Here is why that combination matters.
Photo: National Aeronautics and Space Administration European space agency, Canadian Space… / Wikimedia Commons, Public domain
The James Webb Space Telescope, a joint mission of NASA, the European Space Agency and the Canadian Space Agency, launched on an Ariane 5 rocket from French Guiana on 25 December 2021. Its job is to see light that left the first galaxies more than 13 billion years ago.
Why infrared
As the universe expands, light from very distant galaxies is stretched to longer wavelengths. Light that started out visible or ultraviolet arrives at Earth as infrared. Infrared also passes through clouds of dust that block visible light, which is why Webb can show young stars still wrapped in the gas they formed from.
A big mirror kept very cold
Webb's primary mirror is 6.5 metres across and made of 18 hexagonal segments of gold-coated beryllium. Because warm objects glow in infrared, the telescope has to stay extremely cold. A five-layer sunshield about the size of a tennis court blocks heat from the Sun, Earth and Moon.
The telescope orbits around the second Lagrange point, about 1.5 million kilometres from Earth on the side facing away from the Sun. From there, the Sun, Earth and Moon stay on the same side of the shield.
The Cosmic Cliffs
NASA released Webb's first full-colour images on 12 July 2022. One of them shows the "Cosmic Cliffs", the edge of a young star-forming region called NGC 3324 in the Carina Nebula, about 7,600 light-years away. The bright ridge is gas and dust being carved by radiation from hot, young stars above it. Inside the cliffs, Webb picked out stars that earlier telescopes could not see.
🌟 A star is born! Behind the curtain of dust and gas in these “Cosmic Cliffs” are previously hidden baby stars, now uncovered by Webb.
— NASA Webb Telescope (@NASAWebb) July 12, 2022
What to watch
Astronomers use Webb to measure the light of distant galaxies, study the atmospheres of planets around other stars and follow how stars and planets form. Each new data release adds to a picture of how the first galaxies grew.
