‘Bit of Panic’: Astronomers Forced to Rethink Early JWST Findings

‘Bit of Panic’: Astronomers Forced to Rethink Early JWST Findings

Astronomers have been so eager to use the new James Webb Space Telescope, that some have gotten ahead of themselves. Many started analysing Webb data right after the first batch was released, on 14 July, and quickly posted their results on preprint servers–but are now having to revise them. Some astronomers forgot to mention that the telescope’s detectors hadn’t been calibrated properly when the first data were released.

The revisions have not yet appeared to significantly change many of the exciting early results such as the discovery a few candidates for the most distant galaxies ever spotted . Astronomers are now having to accept the limitations of Webb’s early data.

Figuring out how to redo the work can be “thorny” and “annoying”, according to Marco Castellano, an Italian National Institute of Astrophysics in Rome. Garth Illingworth (an astronomer at University of California, Santa Cruz) says that there has been “a lot of frustration”. Guido Roberts Borsani, an astronomer from the University of California Los Angeles, adds, “I don’t think anybody expected this to become as big of an problem as it is.”

Calibration can be difficult for projects that require precise measurements of brightness of astronomical objects such as faraway galaxies. Some astronomers have been trying to find workarounds for several weeks in order to continue their analyses. The Space Telescope Science Institute (STScI), Baltimore, Maryland, will be updating Webb’s calibrations in the coming weeks. These updates will reduce error bars on the telescope’s calibrations, which were a problem for some astronomers in certain areas. They should also reduce the number of percentage points that are affecting astronomers. As calibration efforts continue over the next months, data accuracy will improve.

This is the first publicly released scientific image from the Webb telescope, showing a deep-field look at the sky that includes many distant galaxies.
This image is the first to be publicly released from the Webb telescope. It shows a deep-field view of the sky, including many distant galaxies. Credit: NASA, ESA and STScI
. Credit: NASA, ESA, CSA and STScI

The STScI pointed out that initial calibrations of the telescope were not perfect, according to Jane Rigby (operations project scientist for Webb) at NASA’s Goddard Space Flight Center, Greenbelt, Maryland. Much of the issue stems from the fact that Webb, which launched in December 2021, is a new telescope whose details are still being worked out. Rigby states that it has been a while since the community had a new telescope in space. “It’s been an extended time since we had one of these powerful transformative powers,” Rigby said.

” We knew it wasn’t going to be perfect out of the box,” said Martha Boyer, an STScI astronomer who is leading the calibration efforts.

Calibration controversy

All telescopes must be calibrated. This is usually done by observing a well understood star, such as Vega. Astronomers compare the data collected by telescope’s different instruments, such as the star’s brightness in different wavelengths of sunlight, with laboratory standards and measurements from other telescopes.

Working with Webb data requires several types of calibration. However, the current controversy revolves around the Near Infrared Camera (NIRCam), one of the telescope’s main instruments. STScI researchers worked for six months to calibrate NIRCam within the six months following Webb’s launch. Due to Webb’s demands, they were unable to calibrate it in the six months that followed. They had to point it at one or a few calibration stars and take data using one of NIRCam’s ten detectors. The calibrations of the remaining nine detectors were then calculated. Boyer states, “That’s where there was trouble.” “Each detector will have a slightly different .”

Within days of the initial Webb data release multiple candidates for the largest distant galaxy ever documented began appearing on arXiv’s preprint server. These studies were based on the brightness of distant objects measured with Webb at different wavelengths. Then, on 29 July, the STScI released an updated set of calibrations that were substantially different from what astronomers had been working with.

” This caused a bit of panic,” Nathan Adams, an astronomer from the University of Manchester, UK, said. He and his colleagues pointed out the problem in a 9-August update to a preprint that they had posted in late August. “It was a bit of a panic for those who had written papers within the first two week.

A young observatory

To standardize all measurements, the STScI has developed a detailed plan to point Webb to several types of well-understood stars and observe them with every detector, in every mode, for every instrument on a telescope. Karl Gordon, an STScI astronomer who leads the effort, says that it takes a while.

Astronomers have been working on manuscripts that describe distant galaxies based on Webb data. Adams states that everyone has reexamined the manuscripts and found it to be less bad than we thought. Many of the most exciting distant galaxy candidates are still at or close to the distance originally calculated. However, other preliminary studies, such those that compare large numbers of faint galaxies to draw conclusions about the early Universe, may not be able to withstand the test of time. These preliminary brightness measurements are less important for other research fields, such as planetary studies.

” We’ve realized how important this data processing is an ongoing, developing situation just because the observatory are so young,” says Gabriel Brammer (an astronomer at University of Copenhagen) who has been developing Webb calibrations that are independent of the STScI.

In the long-term, astronomers will be able to correct the calibration and feel more confident in their conclusions. Boyer states that for now, astronomers should proceed cautiously. The results they get today may not be accurate six months later, once we have more information. It’s just sort of, ‘Proceed at your o

Read More