A press conference was held on July 12 to present the first images from the James Webb Space Telescope.
Along with a hundred scientists from the Harvard-Smithsonian Center for Astrophysics, I followed the live broadcast from the Phillips Auditorium at the same center.
We already had the Hubble telescope in space. Now we also have the 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.
So why is Webb 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 has 25 m2. So Webb collects 6.2 times more light.
- Webb is better located. Hubble is orbiting the Earth, 550 km above our heads. So the Earth itself hides part of the sky from it [1]. As shown in the following figure (not to scale), Webb is at the “Lagrange point” L2, about 1.5 million kilometers from Earth. The result is that no part of the sky is hidden from Webb.
- Hubble is sensitive to visible light. Webb is sensitive to infrared light. Here is a very clear comparison of the 2 sensitivity ranges. Infrared light penetrates best through the gas and dust found in the universe. In addition, the redshift of very distant objects causes their light to reach us in the infrared. Finally, “cold” objects, such as exoplanets, tend to emit infrared light.
- Infrared detection instruments require a low and stable temperature. The L2 point provides it naturally. An Earth orbit no.
These strengths should allow progress in the study of the objectives mentioned above:
- Distant universe: first stars and galaxies formed after the Big Bang, formation and evolution of galaxies.
- “Cold” targets: formation of stars and planets, extrasolar planetary systems.
Meanwhile, the first images are spectacular. My neighbors, who would have every reason to be fed up, while spending their lives studying these images, couldn’t contain their “oh” and “ah” when they saw Webb’s photos.
The loudest exclamations were for the following image. For comparison, I put the same, taken by Hubble. I don’t have to add anything else.
Image of the Carina Nebula taken by the James Webb Space Telescope. / NASA.
Image of the Carina Nebula taken by the Hubble Telescope. / NASA.
Antoine Bret, Professor of Physics at the University of Castilla-La Mancha (Spain).
1. If the Earth were a basketball, the Hubble would be 2 cm from its surface. This means that almost half of the sky is permanently hidden.