Penn State University: Sloan Digital Sky Survey’s robots turn their eyes to the sky

After 21 years, the Sloan Digital Sky Survey — an ongoing effort to map the universe by an international collaboration that includes Penn State scientists — is now seeing the cosmos through “robotic eyes.” Following more than five years of design, development and construction, survey members worked over the final months of 2021 to install a new robotic focal plane system on the Sloan Foundation 2.5m Telescope at Apache Point Observatory, ​​replacing a time-intensive nightly manual process.

“This is a tremendous advance in the capabilities of the SDSS instrumentation,” said Donald Schneider, distinguished professor of astronomy and astrophysics at Penn State and a member of the executive committee of the SDSS Advisory Council. “For over two decades the SDSS has been making fundamental contributions to our understanding of the cosmos from the properties of our galaxy to the large-scale structure and evolution of the universe. The new system will considerably enhance the efficiency of our ability to collect data.”

Previously, hundreds of optical fibers were plugged into small holes in heavy aluminum plates by hand each night. ​​Each of the holes align with a particular star or galaxy when placed on the telescope. Light passing through these holes would travel through the fibers into a spectrograph, which splits the light into a spectrum of wavelengths that provides important information about the light’s source.

The system of preparing plates has been replaced by hundreds of high-precision robots that can position fibers anywhere in the focal plane. The system now installed at the Apache Point Observatory is the first of two units; its twin is currently under construction and will soon head to Las Campanas Observatory in Chile to survey the southern sky.

“We are thrilled to have reached this technological milestone despite being in the midst of a global pandemic and are excited to witness how this shift will enhance the work of the project,” said Juna Kollmeier, director of this fifth phase of the SDSS and the director of the Canadian Institute for Theoretical Astrophysics at the University of Toronto. “This project has been truly collaborative, involving the contributions of scientists at more than 50 institutions from around the world.”

The development of the new robotic focal plane system is a global effort built by an international team, led by Ohio State professor Richard Pogge, and includes Ohio State University’s Imaging Sciences Laboratory, the University of Washington, École Polytechnique Fédérale de Lausanne and the Carnegie Observatories in Pasadena. These design teams overcame numerous challenges posed by the global pandemic by developing and constructing components wherever they were — some in their own garages and backyards — and shipping them elsewhere for further assembly. The robots were built in Switzerland and integrated into the main mechanical units in Columbus, Ohio. From there, they traveled to their final home in New Mexico — and soon, they will head to Chile as well.

The focal plane system will support two of the three core science programs in SDSS-V: the Black Hole Mapper and the Milky Way Mapper. Together, these projects will collect data from millions of objects spread across the sky, from stars in our own galactic backyard to unimaginably distant supermassive black holes.

Penn State astronomers have participated in the SDSS since the first phase of the survey in the late 1990s and are heavily involved in the Black Hole Mapper project. The Black Hole Mapper will study quasars, extremely luminous objects that are thought to be powered by black holes at the centers of galaxies.

“The Black Hole Mapper will obtain spectra of more than 300,000 quasars; this information will be used to understand the inner workings, environments and evolution of quasars, which harbor enormous black holes with masses of tens of millions to billions of times larger than the sun,” said Penn State Professor of Astronomy and Astrophysics Michael Eracleous, who is a member of the Black Hole Mapper Executive Committee and co-chair of the Black Hole Mapper Quasar Physics Science Working Group.

By observing these objects many times and combining the data with earlier SDSS observations, SDSS-V will be able to see how these systems evolve on timescales ranging from days to decades. The survey will also provide observations of hundreds of thousands of cosmic objects originally identified at X-ray wavelengths by the SRG/eROSITA satellite to determine their nature and distance from Earth. This vast sample of sources will include not only new quasars, but also distant clusters of galaxies — the largest gravitationally bound structures in the universe — as well as nearby X-ray-emitting stars.

“I’m excited to measure direct black-hole masses for X-ray–detected active galaxies and investigate powerful quasar winds with the new Black Hole Mapper data,” said Niel Brandt, Verne M. Willaman Professor of Astronomy and Astrophysics at Penn State and a member of the SDSS collaboration.

The Milky Way Mapper will study our home galaxy in unprecedented detail. The ecosystem of stars, gas, dust and dark matter in large galaxies like our own has been shaped over billions of years by numerous physical processes that dominate on different scales in space and time. It will take advantage of our unique perspective within the Milky Way Galaxy to create a uniquely high-resolution map of the galaxy’s stars and how they are moving.

“The SDSS team is an inspiration,” said Kollmeier about the challenges of the past two years “While the world was shutting down, they were showing up. Everyone from the undergraduate students to the project leadership to our industry partners kept at it as best they could and supported each other to get here. I am so proud of this team’s perseverance, and I look forward to the mysteries we will both solve and uncover as the survey gets underway in full force.”