AMADO, Ariz. and Barnard College, NEW YORK, January 16, 2019 – A new telescope, the first of its kind, will be unveiled Thursday on its journey to helping scientists capture faint traces of some of the most distant and explosive events in the universe. At a ceremony at the Fred Lawrence Whipple Observatory in Amado, Arizona, researchers will present the prototype Schwarzschild-Couder Telescope (pSCT), an advanced instrument for studying supernovas and other astrophysical sources of high-energy gamma rays.
The telescope was designed by a collaboration of U.S. institutions, including Barnard College. The pSCT was made possible by funding through the U.S. National Science Foundation Major Research Instrumentation program and by the contributions of thirty institutions and five critical industrial partners across the United States, Italy, Germany, Japan, and Mexico. If successful, more like it may be built as part of a hemisphere-spanning network of telescopes that will act as one, enabling the next generation of gamma-ray astronomy.
This telescope is the first of its kind, and to have that opportunity come up is really exciting,” said Reshmi Mukherjee, Helen Goodhart Altschul Professor of Physics & Astronomy at Barnard College and the principal investigator at Barnard on the project.
Large optical telescopes use bowl-shaped mirrors to collect visible light rays and focus them for observation. Gamma-ray telescopes measure gamma radiation, which is the shortest-wavelength light there is and the most energetic. Gamma rays (or photons, as light can be considered a wave or a particle) are filtered by the Earth’s atmosphere before they reach ground-based telescopes. However, when a gamma-ray photon strikes a particle in the atmosphere, the collision produces flashes of blue light called Cherenkov radiation. Mirrors on the ground can capture and focus that light on a camera, which records the image at a very rapid rate.
The German physicist Karl Schwarzschild proposed the two-mirror telescope design in 1905, and the French astronomer André Couder modified the design soon after, but for a century an actual telescope of their design was too difficult to build, because of the precision required in the mirrors. Finally, technology has caught up, thanks to critical research at both the Brera Astronomical Observatory and Media Lario Technologies Incorporated in Italy. In the SCT, a mirror facing the sky focuses light on a smaller mirror facing it, which focuses the light on a camera between the two mirrors. This extra step allows for a smaller, more sensitive camera. “There is a lot of need to get these high-resolution, high-energy images, which we just haven’t been able to measure yet,” Mukherjee said.
Three major gamma-ray astronomy facilities are currently in operation, using technology a decade or more old: MAGIC, in the Canary Islands, HESS, in Africa, and VERITAS, at the Whipple Observatory in Arizona. Each combines the signals from two to five telescopes. “These have been very successful, path-finder observatories, but now there’s a huge effort to think of the next step,” said Mukherjee, who is the elected spokesperson of the approximately 100 scientists using VERITAS. That next step is the Cherenkov Telescope Array (CTA), planned for operation in 2023. CTA will be the first ground-based gamma-ray astronomy observatory open to the worldwide astronomical and particle physics communities. (For more information visit https://www.cta-observatory.org.)
The CTA will consist of 118 telescopes, divided between two locations, in Spain in the northern hemisphere and Chile in the southern hemisphere. The telescopes will be of three sizes, to best capture Cherenkov bursts of three different sizes. If the prototype Schwarzschild-Couder Telescope is successful, SCTs may play the role of the medium-sized telescope for CTA.
The prototype SCT’s primary mirror is 9.7 meters across and its smaller mirror is 5.4 meters across. Each is composed of dozens of mirrors tiled together, easing construction. The mirror segments also use what’s called active alignment: they swivel on computer-controlled motors to compensate for any distortion caused by the weather or structural sag. The entire telescope weighs 80 tons. And yet it can point to any part of the sky within 90 seconds. “The goal is to get to a target as quickly as possible,” Mukherjee said, “because otherwise you miss the fireworks.”
The telescope’s camera can currently record about 1600 pixels, but Mukherjee and Barnard recently received a grant from the National Science Foundation to upgrade the camera to one with more than 11,000 pixels. With a factor of ten more imaging pixels than in a single-mirror design of the same size, the SCT will offer unprecedented details of air shower images.
The prototype SCT was first funded by the NSF in 2012, led by Vladimir Vassiliev of the University of California, Los Angeles. “It’s great to see it constructed,” Mukherjee said. “In the last few years there were times when it seemed like we were lost in the nitty gritty. Now we can move on to the next phase.” Data collection will begin early this year. Barnard and Columbia post-doctoral fellows, graduate students and undergraduates are currently working on software for aligning the mirrors and operating the camera and on commissioning the telescope.
“I’d say the most exciting things I feel about my work on the pSCT are the unknowns and the versatility,” said Qi Feng, a post-doctoral research scientist at Barnard College and Nevis Labs, Columbia University. “The new design means we don’t know how much we can optimize the telescope’s performance.”
VERITAS will continue operating for the next three to five years as the Cherenkov Telescope Array is constructed, and data from VERITAS and the SCT may be combined. If SCTs become part of the Cherenkov Telescope Array, their use will be open to any scientist who successfully proposes an observation for the array – the first time in gamma-ray astronomy for such an open system.
Observations might include supernovas, or pulsars – dense spinning stars that emit beams of radiation, also known as blazars – galactic nuclei, outside the Milky Way, with discs of matter furiously swirling around super-massive black holes, that shoot jets of particles toward Earth. “This is astronomy at the highest energies,” Mukherjee said. “We look at the most powerful accelerators in the universe,” pushing particle to energies orders of magnitude greater than anything achievable at the Large Hadron Collider, at CERN. And the source can be distant. “Sometimes we measure light from halfway across the universe.” One key mystery is what are called “unidentified sources,” which are known to exist because they emit gamma rays, but that are otherwise invisible, undetectable with optical or radio or X-rays. “We want to understand what they are,” Mukherjee said. “It’s a puzzle.”
“The prototype SCT highlights three important things,” said Linda Bell, Provost and Dean of the Faculty at Barnard College. “One is the power of collaborative science, with multiple institutions working together. Second is the value and importance of federal support for projects of this scope; the project wouldn’t be possible without the generous support – more than $3 million – from the National Science Foundation. Finally, in a field with so few women, it is an amazing honor to have a woman from Barnard College in such a prominent role. It reflects first on what Mukherjee has accomplished, and secondly on Barnard as a place to do meaningful research.”
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Photo credit for lede image: Amy Oliver, Fred Lawrence Whipple Observatory, Center for Astrophysics | Harvard & Smithsonian. Used with permission.