Interview with Yaël Nazé, FNRS senior research associate within the ‘Groupe d'Astrophysique des Hautes Énergies’ (GAPHE) of the STAR Institute at ULiège.
The JWST is presented as a revolution for the study of the universe. Why?
The telescope will be extremely sensitive, allowing it to observe things never before seen in our universe. For example, it should be able to observe the very first generation of stars, those that ended the 'dark ages' of the cosmos (a period of a few hundreds of millions of years after the Big Bang).
It is also a 'monster', the largest space telescope ever put into orbit. How big is it?
When fully deployed, the telescope's protective shield will cover an area of 22m by 12m, the size of a tennis court! On the mirror side, this telescope has a mirror 6.5m in diameter, almost three times the size of the Hubble telescope. As a scientific mission, the James Webb is the largest structure ever deployed in space.
What equipment is on board? What kind of data will it collect and send back to Earth?
There are two types of instruments on board. First, there are cameras that will take images and then there are spectrometers that will record 'spectra'. While we are familiar with the concept of images, 'spectra' seems a little more exotic. They actually show how light is distributed according to energy, so spectrometers are much like rain spreading sunlight into a rainbow. This rainbow is important as it contains the signatures of elements and molecules: by analyzing it, we can understand what stars are made of.
The JWST will be positioned at the L2 Lagrange point. Why?
To get some peace and quietness! Indeed, at this point, the Earth and the Sun are always in the same direction. It is therefore easier to protect oneself from these two major sources of disturbance. Hidden behind its protective shield, the James Webb will remain in very stable conditions, allowing it to achieve unprecedented accuracy.
How is JWST different from Hubble, as it is presented as its successor?
Firstly, it is much more sensitive: it will collect six times more light thanks to its large mirror. Secondly, it will be installed much further away: Hubble is barely 500 kilometers from Earth, while James Webb will be 3000 times further away, at 1.5 million kilometers. This will give it better observing conditions, but will prevent any repair or improvement mission. Finally, Hubble mainly observes the cosmos in the visible and ultraviolet light, whereas the James Webb will scan the mid-infrared: this allows it to study cooler objects (such as exoplanets) and the molecules that make them up, or stars located at the edge of the universe (and observable in this colour because of the expansion of the universe). However, because of observing in this 'colour', the James Webb must be cooled to -230°C (whereas Hubble does not need this).
What is its theoretical lifetime?
Officially 5 to 10 years... but let's be clear, if all goes well, scientific missions are often extended, so we expect a little more than that - even if the Hubble longevity won't be reachable because Hubble benefited from improvement in missions carried out by astronauts and the James Webb will be too far away for that...
The scientific community is very impatient. How is the sharing of observation time organized, and how are scientific projects selected?
As with all observatories! First there is a call for proposals. Astronomers must then fill a form describing what they want to observe, why and how. They also need to mention the expected results and their importance for the advancement of knowledge. Other astronomers read all these projects and choose the ones they think are best. But of course, there is not enough time for everyone! For the first selection of the James Webb, there were four times as many projects as there was time available, which is not that large (the Hubble and XMM space telescopes often exceed a pressure factor of six), but still leads to a lot of disappointments.
In which areas should we expect major discoveries in the next few years?
Many results are expected in the field of exoplanets, as well as in the frontiers of the universe and cosmology.
Is the post-JWST era already being considered? Are there even more ambitious projects in the pipeline of the major space agencies?
Of course! Astronomical projects are planned well in advance because they take at least a decade to set up. In the next few years, we will have telescopes on Earth with a diameter of 30 to 42 metres. And in space, there will be a large planetary mission to Jupiter (JUICE) and two large astrophysical missions (Athena, an observatory dedicated to X-rays, and LUVOIR, a 'twin' of JWST observing in ultraviolet). Liège astronomers are involved in all these projects.
