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The first image has been released with all 18 of the JWST's mirrors powers combined. It may be an image of an ordinary star but astronomers are almost speechless with excitement at the capability demonstrated in this one incredible image.
“More than 20 years ago, the Webb team set out to build the most powerful telescope that anyone has ever put in space and came up with an audacious optical design to meet demanding science goals,” said NASA's Dr Thomas Zurbuchen in a statement. “Today we can say that design is going to deliver.”
On every measure the JWST's optics are matching or beating expectations, leading NASA's Dr Ritva Keski-Kuha to say: “We now know we have built the right telescope,” something many doubted during the telescope's long delays.
The image above marks the end of the stage known as “fine phasing”. The mirror's performance so far has been so good that the JWST's operators are confident the largest space telescope ever deployed will meet, and likely exceed, the scientific goals for which it was built.
One of the most important criteria for a telescope is resolution, the smallest thing that can be distinguished with it. The image provided has a resolution 70 milliarc seconds, which is 28 times as fine as the Spitzer Space Telescope, the previous most powerful infrared telescope. The performance is similar to that of Hubble (after correction) but at longer wavelengths that Hubble can't see,
The JWST's 6.5-meter (21-foot) primary mirror is constructed out of 18 hexagonal mirrors, both to make it easier to build and so it could be folded up for launch. Getting these, and the secondary and tertiary mirrors, aligned is a slow process. Once the wing mirrors had been successfully unfolded NASA described seven stages still required before the first research-quality images could be acquired, sometime around June or July this year.
The course and fine phasing stages were listed as number four and five, but were an iterative process, with one then the other repeated three times. The point of phasing is to make the mirror's components act as a single large mirror, rather than the 18 separate ones that it was previously. However, fine phasing will need to occur on a routine basis throughout the telescope's operational life to correct for any misalignments that creep in.
To demonstrate the success of the phasing stages, the JWST's operators focused on the bright star 2MASS-J17554042+6551277. Bright here being a rather relative term, since this star is too faint to be seen with common binoculars, let alone the naked eye, which is why it has such an uncatchy name. Nevertheless, it's bright enough to create the bright arms where its light leaks into surrounding pixels. Galaxies (one of which is 4.8 billion light-years away) and much fainter stars can be seen in the background.
The JWST has multiple instruments that can collect and process its light in different ways. Completion of fine phasing means the telescope is aligned at one point in its field of view, which allows the main detector, the Near Infrared Camera to operate effectively. We are still months away from all instruments being able to operate together, but there is now little doubt this will be achieved.
