Revived technology used to count individual photons from distant galaxies

Using an instrument on the Southern Astrophysical Research Telescope 4.1 meters, researchers have obtained the first astronomical spectrum using a charge-coupled device (CCD).

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

“This is a major milestone for skipper-CCD technology,” said Alex Drlica-Wagner, a cosmologist at the US Department of Energy’s Fermi National Accelerator Laboratory, who led the project. “It helps draw out the perceived risks of using this technology in the future, which is extremely 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 cluster. LDRD is a DOE-sponsored national program that allows national laboratories to domestically fund 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-dimensional arrays of light-sensitive pixels that convert incoming photons into electrons. Conventional CCDs are the image sensors first used in digital cameras, and they 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 distributions of stars and galaxies. To do this, they need advanced technology that can see fainter and more distant astronomical objects with as little noise as possible.

Existing CCD technology can make these measurements, but it takes a long time or is less efficient. So astrophysicists must either increase the signal – ie. investing more time in the world’s largest telescopes – or reducing 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 multiple measurements of interesting pixels and discarding the rest. This strategy enables head CCDs to increase the accuracy of measurements in regions of interest in the image while reducing the total readout time.

In 2017, scientists began using manned CCDs for dark matter experiments such as SENSEI and OSCURA, but the 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 Captain CCD on the SOAR Integral Field Spectrograph to collect astronomical spectra from a cluster of galaxies, two distant quasars, a galaxy with bright emission lines, and a star that is potentially associated with matter. dark. -ultra-faint dominated galaxy. In a first for astrophysical CCD observations, they achieved sub-electron readout noise and counted individual photons at optical wavelengths.

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

Researchers are analyzing data from these first observations, and the next scheduled run for the skipper-CCD instrument on the SOAR telescope is in July 2024.

“It’s been many decades since Captain was born, so I was surprised to see the technology come back to life so many decades later,” said Jim Janesick, the inventor of Captain CCD and a distinguished engineer at SRI International, a research institute based in in California. “The noise results are amazing. I was floored when I saw the very clean data.”

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

The next generation of captained CCDs have been identified for use in future DOE cosmology efforts, such as the DESI-II and Spec-S5 spectroscopic experiments, recommended by the recent US particle physics planning process. Additionally, NASA is considering captain CCDs for the upcoming Habitable Worlds Observatory that will attempt to detect Earth-like planets around Sun-like stars.

“I can’t wait to see where these detectors can end up,” said Marrufo Villalpando, who joined the program in 2019. “People are using them for amazing things everywhere; their utility ranges from particle physics to cosmology. It’s very versatile and useful technology.”

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