Innovative technology used to count individual photons from distant galaxies

Using an instrument on the 4.1-meter Southern Astronomical Research Telescope, researchers have obtained the first on-sky spectrum using captain-coupled devices (CCDs).

The results were presented on June 16 at the Society of Photo-Optical Astronomical + Instruments Engineers meeting in Japan by Edgar Marrufo Villalpando, Ph.D. candidate at the University of Chicago and a Fermilab DOE Instrument Research Award Fellow.

“This is a big step forward for captain-CCD technology,” said Alex Drlica-Wagner, an astrophysicist at the Energy Department’s Fermi National Accelerator Laboratory, who led the project. “It helps to retire the perceived risks of using this technology in the future, which is very important for future DOE cosmology projects.”

This is a significant achievement for a project conceived and initiated through the Laboratory Directed Research and Development Program at Fermilab in collaboration with NSF’s NOIRLab detector group. LDRD is a national program funded by the DOE that allows national laboratories to fund internal research and development projects that explore new ideas or concepts.

CCDs were invented in the United States in 1969, and forty years later scientists were awarded the Nobel Prize in Physics for their achievements. The devices are two-by-two arrays of light-sensitive pixels that convert incoming photons into electrons. Conventional CCDs were the image sensors first used in digital cameras, and remain the standard for many scientific imaging applications, such as astronomy, although their accuracy is limited by electronic noise.

Cosmologists seek to understand the mysterious nature of dark matter and dark energy by studying the distribution of stars and galaxies. To do this, they need advanced technology that can see the faintest, most distant objects in the sky with as little noise as possible.

Existing CCD technology can make these measurements, but it takes a long time or is inefficient. Astronomers must therefore increase the signal—that is, by investing more time in the world’s largest telescope—or reduce electronic noise.

Skipper CCDs were introduced in 1990 to reduce electronic noise to levels that allow measurement of individual photons. They do this by taking many measurements of interesting pixels and skipping others. This strategy enables the CCD captain to increase the accuracy of the measurements in the regions of interest of the image while reducing the total reading time.

In 2017, scientists pioneered the use of a CCD probe for dark matter experiments such as SENSEI and OSCURA, but a new presentation marked the first time the technology was used to observe the night sky and collect astronomical data.

On March 31 and April 9, researchers used the twin CCDs on the SOAR Integral Field Spectrograph to collect astronomical images from a cluster of galaxies, two distant quasars, a galaxy with bright emission lines, and a star that may be associated with dark matter. -dominated by a very faint galaxy. In the first time with a space-based CCD probe, they found the noise of small electron readouts and counted individual photons at optical wavelengths.

“What’s amazing is that these photons traveled to our detectors from objects billions of light years away, and we can measure each one individually,” Marrufo Villalpando said.

Researchers are analyzing data from this first observation, and the next scheduled run of the captain-CCD instrument on the SOAR Telescope is in July 2024.

“Decades have passed since the captain was born, so I was surprised to see the technology alive again decades later,” said Jim Janesick, the inventor of the CCD captain and a distinguished engineer at SRI International, a US-based research institute. California. “The results of the noise are amazing. I fell off my chair when I saw such clean data.”

With the first successful demonstration of skipper-CCD technology for astronomy, scientists are already working to improve it. The next generation of CCD captains, developed by Fermilab and Lawrence Berkeley National Laboratory, is 16 times faster than current devices. These new devices will significantly reduce study time, and researchers have already begun testing them in the laboratory.

The next generation of CCD captains has been identified for use in future DOE cosmology efforts, such as the DESI-II and Spec-S5 observational experiments, proposed by the recent US physics planning process. Additionally, NASA is considering a CCD captain for the upcoming Habitable Worlds Observatory unit that will attempt to discover Earth-like planets around Sun-like stars.

“I’m looking forward to seeing where these detectors can end up,” said Marrufo Villalpando, who joined the program in 2019. “People are using them for amazing things all over the place; their applications range from particle physics to cosmology. Many and important technologies.”

The project was a close collaboration between physicists, astronomers and engineers at Fermilab, UChicago, the National Science Foundation’s NOIRLab, the DOE’s Lawrence Berkeley National Laboratory, and Brazil’s National Astronomy Laboratory.