But the diameter of its mirror is only 2.4m, and the power of a telescope scales with the square of the diameter of the mirror. It's been a pioneering facility, for sure. It's also not a particularly large telescope. "The limiting factor we have with Hubble, for example, is that it doesn't reach far enough into the infrared to detect the starlight signal we want. We call it redshift," explains Richard Ellis, a University College London astronomer who's impatient to explore the end of the dark ages. "Distant starlight gets stretched by the expansion of the Universe and shifts into the infrared region of the spectrum. Webb, on the other hand, is set up specifically to detect longer wavelengths, which, although invisible to our eyes, are exactly in the regime where the glow from the most distant objects in the Universe will show up. That's the same type of light we detect with our eyes. Hubble was designed to be sensitive to light predominantly at optical, or visible, wavelengths. Webb has, however, been tuned to look at all its targets in a very particular way. It should be particularly adept at studying planets around other suns. It'll observe just about everything there is to see out there beyond Earth - from the icy moons and comets in our own Solar System to the colossal black holes that seem to reside at the core of all galaxies. The emphasis on the search for the first starlight makes Webb sound like a "one note flute". It's already burned for nearly five billion years and will probably keep on burning for another five. Our own Sun seems so timid in comparison. And so these early stars might have only lasted at most a million years or so." "And, in fact, all stars follow the rule that the length of time they can exist as a star is inversely proportional to their mass - meaning, the more massive a star, the faster it uses up its fuel. "Estimates range from anywhere of order 100 to 1,000 times the mass of our Sun," says Marcia Rieke, the principal investigator on Webb's NIRCam instrument. We can put the laws of physics into computer models and run them to get a sense of what might be possible. We don't know much about the first stars. It's absolutely amazing to me that we could actually observe that process in progress." "It's about the formation of the first carbon atom ever. "Webb's mission is about the formation of all likeness it's the 'we're all made of stardust' argument," ponders Rebecca Bowler, a University of Oxford astronomer who's a team-member on Webb's NIRSpec instrument.
If you keep probing deeper and deeper, you should eventually get to retrieve the light from the pioneer stars as they group together into the first galaxies. But that's the consequence of light having a finite speed in a vast and expanding cosmos. It's an astounding idea that you might still be able to witness such a thing. There won't be many of them to find at that time but the Webb telescope can see them if they're there, and we're lucky," the US space agency (Nasa) researcher tells a special edition of Discovery on the BBC World Service. "We think there should be stars, or galaxies, or black holes maybe beginning at 100 million years after the Big Bang. "They will be just little red specks," says JWST senior project scientist and Nobel Prize winner John Mather. Simply mesmerising: Webb's huge mirror is made from beryllium coated in goldĮquipped with a 6.5m-wide (21ft) mirror and four super-sensitive instruments, Webb will stare for days at a very narrow spot on the sky to detect light that has been travelling through the immensity of space for more than 13.5 billion years.