Cryogenics, Superconductivity Enabled Historic Black Hole Photograph

by Fariss Samarrai, University of Virginia News Associate,

The world marveled in April at the photo of a supermassive black hole about 55 million light-years from Earth, in the middle of a galaxy called Messier 87, photographed by an international team of astronomers and engineers using a global network of telescopes called “Event Horizon.” Use of cryogenics in superconducting materials minimized the background noise to reveal the black hole, making this accomplishment possible.

Supermassive black holes in the center of massive galaxies are thought to have formed early in the history of the universe. Understanding them provides clues to better understanding galaxy formation and evolution. Black holes grow steadily by continually drawing in more stars, further building their mass and gravitational pull.

Innovations in astronomical instruments made over decades allowed astronomers to take this first-ever photo of a black hole, which looks like a brightly lit circle around a shadowed hole. The shadow is caused by the gravitational bending and capture of light by the event horizon—the border between surrounding material and the black hole’s gravitational pull—indirectly revealing its presence.

Superconducting submillimeter detectors, developed by engineers and astronomers at the University of Virginia and the National Radio Astronomy Observatory in Charlottesville, helped make visible what once was only black.

Astronomers needed detectors that operate at 230 GHz, an exceptionally high frequency that is about 100 times higher than Wi-Fi. These superconducting detectors are highly specialized and refined, requiring years of development and construction.

“Almost all of the specialized superconducting detectors involved in this black hole discovery were developed and micro-fabricated by our research and development group in the UVA Microfabrication Laboratory,” said Dr. Arthur Lichtenberger, UVA professor of electrical and computer engineering and director of the lab that built the detectors. Lichtenberger is also a member of the board of the Applied Superconductivity Conference and will be president for the 2022 conference in Honolulu.

The Microfabrication Lab was responsible for the detectors on four of the nine observatories used in the study at locations in Chile, Arizona, Mexico and the South Pole. They built the detectors at the largest and most sensitive submillimeter radio telescope in the world, the Atacama Large Millimeter/Submillimeter Array in Chile. There were over 150 detectors in total. “These superconducting detectors are at the heart of the radio astronomical telescope, and it is the first component to operate on the electromagnetic signal that traversed the heavens for 55 million years before arriving at our detectors,” Lichtenberger said. “The UVA detectors translate, without introducing noise, the extremely weak, high-frequency information from the region of the black hole.”

“This is the culmination of decades of work developing fabrication processes to realize detectors that have the sensitivity to detect the weak signals emanating from this celestial object,” said Robert Weikle, lab team member and professor of electrical and computer engineering. “If you think about it, it is astonishing; the photons from this black hole have been traveling in space for 55 million years, and the first component these photons encounter at radio telescopes after that journey are superconducting detectors that were made in the basement of UVA’s Thornton Hall.”

The UVA research group collaborated with radio astronomers around the globe for more than 50 years to realize cutting-edge technology for the detection of molecular gas signatures light years and galaxies away.

“The resulting data enables astronomers to map the heavens and create and test new theories about the evolution of star systems, pulsars, quasars and galaxies,” Lichtenberger said. “Hundreds of UVA detectors have been used in astronomical receivers around the world and in space-based missions, including the original detection of Earth’s ozone hole.”

Astronomers combined data from nine telescopes located across the globe. The observations were made over a 10-day period, followed by two years of data analysis. These observations helped to further confirm Einstein’s General Theory of Relativity, and the warping of space-time. ■