The James Webb Space Telescope is the largest and most complex astronomy instrument ever launched. It is now evident that the effort was worth it: the first scientific images of the new telescope demonstrate the performance of its optics and the four instruments that work primarily in the infrared and near-infrared. The very first recording delivered the sharpest and most detailed “deep field” recording of the distant cosmos ever made. Well-known motifs such as the Carina Nebula and the Stephans Quintett – a group of interacting galaxies – appear in a new light. A high-resolution spectrum of the extrasolar gas planet WASP-96 confirms the hope that the Webb telescope can also provide new insights into the atmospheres of exoplanets.
The James Webb Space Telescope is a superlative mission. With its 6.5 meter mirror and highly sensitive infrared optics, this telescope can see sharper and further than anyone before it. At the same time, the transport into space and the subsequent procedure of unfolding and adjusting was more complicated and risky than with any other instrument before. More than 300 individual steps had to be carried out with clockwork precision so that the five-layer solar sail, the size of a tennis court, could be unfolded and positioned and the telescope’s mirrors reached their final configuration. After the telescope, which was launched on December 25, 2021, completed these steps during its flight to its place of use, it has been circling around Lagrange point 2, 1.5 million kilometers away, since the end of January precisely adjusted to a few nanometers in order to guarantee an undistorted, clear image.
Deep Field and Exoplanet Spectrum
Now the time has finally come: the preparations are complete and the James Webb Telescope has started its scientific operation. To get started, NASA selected several target objects and motifs that best illustrate the versatility and possible uses of the telescope. On the evening of July 11, 2022, US President Joe Biden himself presented the first image taken by the Webb telescope: the “First Deep Field” – the deepest and sharpest infrared image of the distant cosmos to date. It shows the galaxy cluster SMACS 0723, which is about 4.6 billion light-years away from us. The high gravity of these galaxies and the dark matter associated with them makes this cluster act like a gravitational lens for thousands of even more distant, fainter galaxies. They are now visible for the first time together with their details in this recording of the Near Infrared Camera (NIRCam). In order to make the extremely faint galaxies visible, the telescope focused on this part of the sky for a total of 12.5 hours. The image shows the galaxies in the near-infrared wavelength range of 0.5 to 0.6 microns.
The second major release from the Webb telescope is not an image but a spectrum: it shows the spectral signature of 1150 light-years distant gas planet WASP-96 b, about 1.2 times the size of Jupiter and half its mass. The telescope’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) has analyzed the light that arrives at Earth as this planet passes in front of its star. Because the elements and molecules contained in the planet’s gas envelope leave behind characteristic absorption lines in the light spectrum, astronomers can use such spectra to determine the composition of the exoplanet’s atmosphere. For the first time, the Webb telescope provides the necessary resolution and sensitivity. The NIRISS instrument can separate the wavelengths of light down to a thousandth of a micrometer and detect even the finest differences in brightness. Its spectral range of 0.6 to 2.8 microns extends further into the infrared than other spectrographs. This makes the Webb telescope particularly suitable for detecting molecules such as water, oxygen, methane or carbon dioxide. In the case of WASP-96 b, the spectrum clearly indicates the presence of water vapor in the gas envelope.
Two “classics” in a new light
Another image from the James Webb telescope shows a “classic”: the star forming region NGC 3324 in the Carina Nebula, 7600 light-years away. Characterized by glowing gases, young, hot stars, and the bubbles blown free by their intense radiation, this nebula has also been imaged several times by the Hubble Space Telescope. The Webb Telescope’s Mid-Infrared Instrument (MIRI) now shows the hot dust clouds, ionized gases and molecules in the glowing clouds more clearly than ever before. The telescope thus makes it possible to make more details of star formation visible and thus to elucidate the associated processes and feedbacks. The image shows the edge of an expanding “bubble” in the glowing gas blown free from the young stars at the top of the image. Where the gases in the edge region are compressed by these processes, new stars can form as a result of the collapse of dense gas clouds.
Another “classic” is among the first images taken by the James Webb telescope: the Stephans Quintet. Also known as Hickson Compact Group 92, this formation of five galaxies offers astronomers a chance to study the interactions of such clusters of stars in more detail. Because four of the five galaxies are so close to each other that they are in gravitational interaction and influence each other in their star formation, the distribution of their gases and their behavior. This is visible, among other things, in the long gas tails of some of these galaxies and the shock waves in some of them. The composite image of data from the Near-Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI) show the details of this group of galaxies some 290 million light-years away. The fifth galaxy NGC 7320 on the left is only 40 million light-years away and therefore only appears to belong to the quintet. In it, the Webb image even makes individual stars visible.
Source: NASA/STScI