"A little panic":Forced to reconsider earlier Webb telescope findings

 

Credit: Nolan Zunk/University of Texas at Austin

Some astronomers have gotten a little ahead of themselves because they have been so eager to use the brand-new James Webb Space Telescope. After the first batch of Webb data was released on July 14, many researchers immediately began analyzing them and posted their findings on preprint servers. However, they now have to revise those findings. When the first data were made available, some astronomers missed the fact that the telescope's detectors hadn't been properly calibrated.

Many of the exciting early results, such as the discovery of several candidates for the most distant galaxy ever observed, do not appear to be significantly altered by the revisions as of yet. However, astronomers are being forced to consider the limitations of Webb's early data by the ongoing calibration process.

According to Marco Castellano, an astronomer working at the Italian National Institute of Astrophysics in Rome, the process of redoing the work is "thorny and annoying. "Garth Illingworth, an astronomer at the University of California, Santa Cruz, states, "There has been a lot of frustration. "Guido Roberts-Borsani, an astronomer at the University of California, Los Angeles, adds, "I don't think anyone really expected this to be as big of an issue as it is becoming."

Projects that require precise measurements of the brightness of astronomical objects, such as dim, far-away galaxies, present a particular challenge for calibration. In order to continue their analyses1, some astronomers have been concocting workarounds for several weeks. The Space Telescope Science Institute (STScI), which is in charge of the telescope and is located in Baltimore, Maryland, is anticipated to release the subsequent official round of adjustments to Webb's calibrations in the coming weeks. These updates ought to reduce the error bars on the calibrations of the telescope from tens of percentage points, which have been causing problems for astronomers in some areas, to a few percentage points .Additionally, as calibration efforts progress over the coming months, data accuracy will continue to rise.

Credit: NASA, ESA, CSA, STScI

Jane Rigby, operations project scientist for Webb at NASA's Goddard Space Flight Center in Greenbelt, Maryland, claims that the STScI made it abundantly clear that the telescope's initial calibrations were imperfect. The fact that Webb, which launched in December 2021, is a brand-new telescope whose specifics are still being worked out accounts for a significant portion of the issue. Rigby says, "The community hasn't had a brand-new telescope in space in a very long time, a big one with these amazingly transformative powers."

Martha Boyer, an astronomer at the STScI who is assisting in the direction of the calibration efforts2, states, "We knew it wasn't going to be perfect right out of the box."

Controversy regarding calibration Every telescope must be calibrated. Typically, this is accomplished by looking up at Vega, a well-known star in the night sky. Astronomers compare the measurements made of the same star by other telescopes and laboratory standards to the data collected by the telescope's various instruments, such as the brightness of the star in various wavelengths of light.

There are many different kinds of calibration for working with Webb data; however, the Near Infrared Camera (NIRCam), one of the telescope's main instruments, is the subject of the current debate. STScI researchers worked to calibrate NIRCam in the six months following Webb's launch. However, due to the demands placed on Webb, they only had time to point it at one or two calibration stars and collect data with just one of the ten detectors in NIRCam. The remaining nine detector calibrations were then estimated. That's where the issue was, according to Boyer. There will be slight differences between each detector.

Non-peer-reviewed papers began to appear on the arXiv preprint server a few days after the initial release of Webb data, presenting a number of contenders for the most distant galaxy ever observed. These studies relied on Webb measurements of the brightness of distant objects at various wavelengths. The STScI then published a new set of calibrations on July 29 that were significantly different from what astronomers had been working with.

According to Nathan Adams, an astronomer at the University of Manchester in the United Kingdom who, along with his colleagues, pointed out the issue in a 9 August update to a preprint they had posted in late July, "This caused a little bit of panic. "It was a little bit of “Oh no, is everything that we’ve done wrong, does it all need to go in the bin?” for those, including myself, who had written a paper within the first two weeks.

A young observatory is working on a detailed plan to point Webb at several types of well-known stars and observe them with every detector and mode on every instrument on the telescope in an effort to standardize all measurements. The STScI astronomer Karl Gordon, who is in charge of the project, says, "It just takes a while."

In the interim, astronomers have been revising manuscripts that use Webb data to describe far-off galaxies. "It's not as bad as we thought, and everyone has gone back and looked at it again," Adams says. It still appears that many of the most exciting candidates for distant galaxies are at or close to the initial distance. However, it's possible that other preliminary studies won't stand the test of time, such as those that compare a large number of faint galaxies to draw conclusions about the beginning of the universe. Because they rely less on these preliminary brightness measurements, other research areas, like planetary studies, are less affected.

Gabriel Brammer, an astronomer at the University of Copenhagen who has been developing Webb calibrations independently of the STScI, says, "We've come to realize how much this data processing is an ongoing and developing situation, just because the observatory is so new and so young." In the long run, astronomers are certain to sort out the calibration and become more confident in their conclusions. However, Boyer states, "I would tell people to proceed with caution — whatever results they might be getting today might not be quite right in six months, when we have more information." For the time being, however, Boyer recommends caution. It basically says, "Proceed at your own risk."