Photons Received: Webb Sees Its First Star – 18 Times

The James Webb Space Telescope is nearing completion of the first phase of the months-long process of aligning the observatory’s primary mirror using the Near Infrared Camera (NIRCam) instrument. The team's challenge was twofold: confirm that NIRCam was ready to collect light from celestial objects, and then identify starlight from the same star in each of the 18 primary mirror segments. The result is an image mosaic of 18 randomly organized dots of starlight, the product of Webb's unaligned mirror segments all reflecting light from the same star back at Webb's secondary mirror and into NIRCam's detectors. What looks like a simple image of blurry starlight now becomes the foundation to align and focus the telescope in order for Webb to deliver unprecedented views of the universe this summer. Over the next month or so, the team will gradually adjust the mirror segments until the 18 images become a single star.

Each unique dot visible in the image mosaic is the same star as imaged by each of Webb’s 18 primary mirror segments, and is a treasure trove of detail that optics experts and engineers will use to align the entire telescope. This activity determined the post-deployment alignment positions of every mirror segment, which is the critical first step in bringing the entire observatory into a functional alignment for scientific operations. NIRCam is the observatory’s wavefront sensor and a key imager. It was intentionally selected to be used for Webb’s initial alignment steps because it has a wide field of view, the unique capability to safely operate at higher temperatures than the other instruments, and is packed with customized components that were designed to specifically aid in the process. NIRCam will be used throughout nearly the entire alignment of the telescope’s mirrors. It is however important to note that NIRCam is operating far above its ideal temperature while capturing these initial engineering images, and visual artifacts can be seen in the mosaic.