The US space agency has reached an important milestone in the preparation of the new James Webb Space Telescope.
Engineers say they have now succeeded in concentrating the $10 billion observatory entirely on a test star. The razor-sharp performance is even better than hoped, they add.
To reach this stage, all of Webb’s mirrors had to be aligned at small fractions of the width of a human hair.
But the agency warns that much work still needs to be done before the telescope can be declared operational.
Lee Feinberg, the NASA engineer who led the development of Webb’s optical elements, described the release of the first well-focused image as phenomenal.
“Not only do you see the star and the peaks of the star’s diffraction, but you also see other stars in the field that are tightly focused, as we expect, and all kinds of other interesting structures in the background,” he told reporters. †
“We’ve done a very detailed analysis of the images we get, and so far we’ve found the performance to be just as good, if not better, than our most optimistic forecast.”
Billed as the successor to the famed Hubble Space Telescope, Webb was launched on December 25 by an Ariane-5 rocket from French Guiana.
The overarching goal is to take pictures of the very first stars to shine in the universe and to investigate distant planets to see if they are habitable.
To give Webb the necessary resolution and sensitivity to accomplish this mission, it was equipped with a 6.5 m wide primary mirror.
But this reflective surface, made up of 18 segments, is so large that it had to be folded to fit the Ariane’s nose cone.
The first tasks since launch were therefore dominated by the requirement to unpack the mirror and other optics and make them all work in harmony.
Each of those 18 segments has its orientation and curvature adjusted by small motors, allowing them to behave as if they were a single, monolithic surface.
“We have now achieved what is called the ‘diffraction-limited alignment’ of the telescope: the images are focused on each other as finely as the laws of physics allow,” said Marshall Perrin, who works on Webb at the Space Telescope Science Institute in Baltimore. , Maryland.
The alignment work was done using one specific instrument on Webb – the main camera system known as NIRCam. Engineers will now have to verify that this setup also works for the three other instrument packs on Webb. This may require some minor changes or even some compromises with the configuration as it stands now, but any changes are not expected to be significant.
The star used for the test image released Wednesday is nothing special, just “a generic, anonymous star” with the correct brightness level.
Webb sees the star at a wavelength of two microns. This is in the infrared; it is not a light that would be seen by the human eye. The red color is for contrast.
The “spike” structures were a function of the design of Webb’s primary mirror, explained Prof. Mark McCaughrean of the European Space Agency (ESA).
“The shape of those 18 hexagons prints a faint diffraction pattern that makes bright stars look like spiky snowflakes – this isn’t a problem for science, but will give Webb images a very distinctive look,” he told BBC News.
“Indeed, the fact that we can see those spikes so sharply also confirms that the mirrors are perfectly aligned — this is brilliant news.”
Take a closer look at the background features in the image. The oval shapes are large galaxies that are probably billions of light years away.
It is important to remember that this is a test image created for technical purposes. The glorious vistas of the cosmos, like the ones Hubble has spoiled us with for the past 30 years, will come later in the summer when science operations begin.
“The technical images we see today are as sharp and clear as the images Hubble can produce, but they are on a wavelength of light that is totally invisible to Hubble,” said Jane Rigby of NASA’s Goddard Space Flight Center in Greenbelt. Maryland. †
“So this causes the invisible universe to be very, very sharp in focus.”
The James Webb Space Telescope is a joint venture of the American, European and Canadian space agencies.
