How does the James Webb telescope work?

And what will this new telescope be able to tell us about the universe?
03 February 2022

Interview with 

Becky Smethurst, University of Oxford


Artist's impression of the James Webb Telescope


As we record this episode, the 10 billion dollar James Webb telescope is moving towards its final destination. We asked astrophysicist Becky Smethurst what we are hoping to see with this telescope, and whether it might be able to tell us a bit more about potential other life forms in the universe…

Becky - 100%. It's one of the main science goals of the James Webb space telescope - or JWST as we call it. So what James Webb has been designed to do is look at infrared light. And this is the key thing with James Webb and why it needs to be so far away and have a giant tennis-court sized sun shield to protect it from infrared light from the sun. But what it'll be able to do is see stuff that the Hubble space telescope physically can't see because it looks at visible light. And the thing is, the light from the very furthest stars and galaxies away from us, the light that was emitted at the very beginning of the universe and is currently still traveling towards us, has been redshifted by the expansion of the universe. So space is expanding and it essentially drags out the light wave as it goes and stretches it along the wavelengths, which are redder. But this has been stretched out so much that when it was emitted as visible light, it is now infrared light. So Hubble has no chance of seeing it at all. It can't even pick it up. It's not that it's just faint, it can't detect it. So this is what James Webb has been designed to do, is to see the light from the first stars and galaxies that there ever was in the universe, essentially to detect the oldest light that is. And so that's what I'm really excited for. It also might answer sort of like a chicken or an egg question - whether the first stars form, make a black hole, and then that become the first super massive black hole that happened to then fall and sink to the centre of a galaxy, because it was the heaviest thing. Or did a super massive black hole collapse from the first gas in the universe and then a galaxy of stars form around it. But then the other thing that the JWST can do because it works in the infrared, is look at the fingerprints of different molecules in terms of the light they absorb or emit. A lot of the key ones for life are in the infrared; water specifically leaves a fingerprint on infrared light so that we know that it's there. So the plan is, for what we call exoplanets, planets that orbit other stars in our galaxy, when they pass in front of the star that they orbit, we can take the tiny amount of starlight that happened to pass through the skinny bit of atmosphere around them, isolate it and work out what molecules are present in that atmosphere and whether water is present there and other indicators of life biomarkers, biosignatures as we call them. We could be in a position in five years time, where we find the most habitable place for life that we've ever seen beyond earth.

Julia - That's pretty cool!


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