Scientists from the James Webb Space Telescope shared the first images from space taken by the new telescope. Since the 18-segment mirror is in the early stages of being aligned, the first image is understandably blurry and a bit jumbled. But its exactly what the team wanted to see.
“The initial results are very similar to our simulations and matches our predictions,” said Lee Feinberg, JWST’s Optical Telescope Element Manager, speaking at a press briefing on February 11, 2021. “We don’t see anything of concern. But this is the first time using the components of the telescope at zero gravity, and the results … shows that the NIRCam (Near Infrared Camera) instrument is an excellent wavefront actuator.”
While the team is not calling these images “first light,” they said the images meant that they have “detected photons from outer space for the first time with the telescope.”
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The first image is a mosaic of 18 images of the same star – one image for each of the unaligned segments. The light from the star was reflected back at Webb’s secondary mirror and into NIRCam’s detectors. The image proves that NIRCam is ready to collect light from celestial objects, and then identify starlight from the same star in each of the 18 primary mirror segments.
Webb scientists assured that the images will become clearer when the mirror segments are aligned to act as one giant 6.5-meter mirror, and also when the telescope and instruments reach their intended operating temperatures. Feinberg said JWST is currently about 60 degrees over the negative 370 degrees Fahrenheit (negative 223 degrees Celsius) optimal operating temperature.
The second picture is a ‘selfie’ of sorts, showing the mirror segments. It was taken with a special lens within the NIRCam instrument, which is meant for engineering, not science, and allows NIRCam to capture an “inward-looking” image of the primary mirror. While all the mirror segments are seeing starlight, the one segment looks bright because, from NIRCam’s view, the segment is directly aligned with the star. This image allows the team to check that the telescope is aligned with the science instruments.
The star that NIRCam is using to help align the mirror segments is HD 84406, a G-type main sequence star that is a lot like our own Sun, located near the ‘bowl’ of the Big Dipper (Ursa Major).
In a blog post about the images, the JWST team said that during the image capturing process that began on February 2, Webb was repointed to 156 different positions around the predicted location of the star and generated 1560 images using NIRCam’s 10 detectors, amounting to 54 gigabytes of raw data. The entire process lasted nearly 25 hours, but notedly the observatory was able to locate the target star in each of its mirror segments within the first six hours and 16 exposures. These images were then stitched together to produce a single, large mosaic that captures the signature of each primary mirror segment in one frame. The images shown here are only a center portion of that larger mosaic, a huge image with over 2 billion pixels.
“This initial search covered an area about the size of the full Moon because the segment dots could potentially have been that spread out on the sky,” said Marshall Perrin, deputy telescope scientist for Webb. “Taking so much data right on the first day required all of Webb’s science operations and data processing systems here on Earth working smoothly with the observatory in space right from the start. And we found light from all 18 segments very near the center early in that search! This is a great starting point for mirror alignment.”
“Not only has the telescope spread its wings but it has now opened its eyes,” said Feinberg.