This upgrade to Pocahontas County’s Green Bank Telescope is a critical advancement for astrophysics research, especially galaxy mapping. Because of the sensitivity of the camera’s receiver, astronomers can now map galaxies seven times faster. The project was many years in the making, starting in 2013.
“This receiver turned out to be as sensitive as the existing receiver on the telescope except we can collect data at seven independent positions simultaneously with the new camera instead of just one,” said Chair and Professor of Physics and Astronomy D.J. Pisano, who studies how galaxies form and evolve. “Only three of these cameras are currently operational in the world, but the Green Bank Telescope’s camera is the most sensitive of its kind.”
The camera, called a phased array feed, contains 19 cross-shaped antennas called dipoles that, while packed closely together, are precisely placed to efficiently capture signals from space. However, it works differently than a digital camera or the cameras found in cell phones. Together, the antennas operate as a large viewfinder, increasing the amount of sky that can be surveyed in a single snapshot. After the signals are captured, it forms the pixels electronically using special software.
“Traditional radio telescopes throughout the world record the information from incoming
radio waves using a single detector. This restricts the amount of the sky that
can be observed at any given time to a very tiny fraction. This is what is known
as the field of view,” said WVU alumnus Nickolas Pingel (Ph.D. Physics, ’17), one
of the original student researchers. “If an astronomer is interested in observing
an object that extends beyond a telescope's inherent field of view, such as a portion
of our own Milky Way, they must move the telescope in a complicated manner that
takes up precious telescope time.”
“Phased array feeds measure the incoming radio waves through not just one but many identical detectors,” Pingel said. “By looking and tweaking how these detecting elements respond to the incoming signals simultaneously, we are greatly expanding the Green Bank Telescope’s field of view. This allows astronomers to work at unprecedented speeds.”
WVU collaborated with researchers at Brigham Young University, the National Radio Astronomy Observatory and the Green Bank Observatory to make this upgrade a reality. WVU’s student team developed the software to translate the signals captured by the camera.
“Our part was all about the computing on the back end. The signal comes from the receiver at the Green Bank Telescope, is digitized and sent down a mile of fiber optics to get to the lab at the Green Bank Observatory where it is fed into high-performance computers,” said Pisano, who will use the camera to map hydrogen gas in galaxies. “Our students were responsible for writing the software that took the signals from those computers and converted them into something you can analyze. They took the raw data and put it all together in a sensible way so it could be useful.”
Pingel created the software that processes the raw data from the camera to produce
maps of galaxies.
“The chance to step into such a critical role in the development of a new radio camera, while a bit overwhelming at first, was too good to pass up,” Pingel said. “This project taught me about good coding practices, how to communicate and work within a collaboration and see firsthand how a project evolves from initial brainstorming sessions to sitting on top of one of the world’s largest radio telescopes. I also became a lot more comfortable working through unforeseen problems in high-pressure environments, especially when things went wrong in testing when the camera was on the telescope.”
Today, Pingel is a postdoctoral fellow at the Australian National University. He
works on the Australian Square Kilometer Array Pathfinder, one of the other radio
telescopes in the world that is consistently equipped with phased array feed technology.
He spent his first year as a postdoc writing and developing code that runs on Australia’s
most powerful supercomputers to convert raw data into maps.
“This technology optimizes the telescope for survey science by expanding the typical field of view almost 3,000 percent,” Pingel said. “I work on the Galactic ASKAP Survey, which uses the telescope to map hydrogen within our own Milky Way and the nearby Magellanic System at unprecedented resolutions.”
The Green Bank Telescope’s new phased array feed can also be used to look for fast radio bursts, pulsars and other astronomical phenomena at speeds two to three times faster than the telescope’s previous instrumentation. Working with Pingel and current WVU physics doctoral student Devansh Argawal, alumnus Kaustubh Rajwade (Ph.D. Physics, ’17) led the effort to develop software to translate that data.
“Working on pulsar data processing software for the camera was a wonderful opportunity for me to be involved in radio astronomy instrumentation,” Rajwade said. “The whole experience of building this tool taught me valuable lessons in radio astronomy software development and instrumentation. I continue to apply this knowledge to my current work.”
After graduating from WVU, Rajwade joined the University of Manchester in England as a postdoctoral research associate. In this role, he leads the software development and deployment of another radio instrument, MeerTRAP. He is inspired by his former adviser, Professor of Physics and Eberly College of Arts and Sciences Associate Dean for Research Duncan Lorimer, who, along with physics student David Narkevic, first discovered fast radio bursts in 2007.
“I am working to build a detection system deployed on the MeerKAT radio telescope to find fast radio bursts in real time,” Rajwade said. “Finding the true nature of these mysterious bursts is an important quest for me.”
Since the completion of Green Bank’s camera, WVU physics doctoral student Evan Smith has been refining the software to make it more user-friendly.
“I have helped streamline the data analysis process to make it easier for both expert and general use by rewriting some of the code and adding a graphic interface to more easily navigate the analysis programs,” he said. “Being part of this project has helped me develop a solid background in digital signal processing – the details of how we turn astronomical signals from space into 'science-ready’ data products.”
This project was funded by a $500,000 award from the National Science Foundation Division of Astronomical Sciences Advanced Technologies and Instrumentation Program.
A new paper, published today (Sept. 21) in the Journal of Astronomical Telescopes Instruments and Systems, reviews 30 years of NSF-supported grants for astronomy technology and instrumentation development. WVU’s Department of Physics and Astronomy hope this new instrumentation will continue to lead to more important breakthroughs in the field of astrophysics.
“The phased array feed on the Green Bank Telescope is the most sensitive of its kind in the world,” Lorimer said. “We look forward to seeing it used more widely by the astronomical community to expedite and enhance their studies and make new discoveries.”
Author's note: Phased array feed image courtesy of Brian Jeffs, Brigham Young