On July 12, a press conference was held to present the first images from the James Webb Space Telescope.
Along with a hundred scientists from the Harvard-Smithsonian Center for Astrophysics, I watched the broadcast live from the center’s Phillips Auditorium.
We already had the Hubble telescope in space. Now we also have James Webb.
When you spend $9 billion on a new telescope, you don’t want it to be a little better than the old one.
Why is the Web so much better than Hubble? That was the first question that came to my mind. My neighbors in the audience responded very well.
- Webb is bigger. The Hubble light collector is 4 m2. Webb’s is 25 m2. So Webb collects 6.2 times more light.
- Webb is better placed. Hubble orbits the Earth 550 km above our heads. So the Earth itself hides part of the sky from it [1]. As shown in the figure below (not to scale), Webb is at the L2 “Lagrange point”, about 1.5 million kilometers from Earth. The result is that no part of the sky is obscured by Webb.
- Hubble is sensitive to visible light. Webb is sensitive to infrared light. Here is a very clear comparison of the two sensitivity ranges. Infrared light penetrates best through the gas and dust found in the universe. Also, the redshift of very distant objects means that their light reaches us in the infrared range. Finally, “cold” objects, such as exoplanets, tend to emit infrared light.
- Infrared detectors require a low and stable temperature. The L2 point provides this naturally. Earth’s orbit does not.
These strengths should make possible progress in exploring the aforementioned goals:
- The distant universe: the first stars and galaxies formed after the Big Bang, galaxy formation and evolution.
- “Cold” targets: star and planet formation, extrasolar planetary systems.
Meanwhile, the first images are impressive. My neighbors, who would have every reason to be fed up as they spend their lives studying these pictures, couldn’t contain their oohs and aahs when they saw Webb’s pictures.
The loudest shouts were for the image below. For comparison, I put the same one taken by Hubble. I don’t need to add anything else.
Photo of the Carina Nebula taken by the James Webb Space Telescope. / NASA.
Hubble Space Telescope image of the Carina Nebula. / NASA.
Antoine Brett, Professor of Physics at the University of Castilla-La Mancha (Spain).
1. If the Earth were a basketball, Hubble would be 2 cm from its surface. This means that almost half of the sky is permanently hidden from it.
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