A Hillsdale College professor and four Hillsdale graduates contributed to a study which revealed a signal found in data from the Arecibo and Green Bank Telescopes that may signify gravitational waves from the merging of two supermassive black holes.
Assistant Professor of Physics Timothy Dolch and students Cody Jessup ‘16, Daniel Halmrast ‘17, Joshua Ramette ‘17, and Michael Tripepi ‘17 worked with the North American Nanohertz Observatory for Gravitational Waves, or NANOGrav, to watch and record pulsars — a type of star “primarily visible to radio telescopes,” Dolch said in an email.
“They are rapidly spinning, collapsed remnants of exploded stars,” Dolch wrote. “Combined with their radio beams, the spinning produces a ‘lighthouse’ effect that makes the radio emission flash on and off or ‘pulse’ — hence the name. These pulsars are spread throughout our Milky Way galaxy.”
According to a Hillsdale College press release, “NANOGrav researchers studied the signals from distant pulsars. Pulsars were chosen because they are detectable and dependable, serving as a sort of galactic clock.”
NANOGrav has been watching 80 pulsars for the last 15 years and looking for “subtle changes in their pulse rates” that might be an indication of gravitational waves, which, according to Dolch, are “ripples in the fabric of spacetime that probably come from merging supermassive black holes that are much more distant — far outside the Milky Way.”
These were recorded using the Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia. Radio telescopes are antennas designed to receive natural radio emissions from space. Radio waves cut through the earth’s atmosphere, making them detectable with ground-based radio observatories. Arecibo was “the best instrument in the world for observing pulsars,” Dolch said.
“Until last December, the main instrument there was the 305‑m William E. Gordon telescope — the big dish that’s commonly known as ‘Arecibo Observatory,’ even though that’s technically the name of the facility housing it,” Dolch said. “You may have seen Arecibo in the movies “James Bond: Goldeneye” and “Contact.” I’ve been there four times, and have even had the experience of walking out on the catwalk to the hanging platform.”
Many Hillsdale students contributed more than 100 hours remotely from the Radio Telescope Remote Command Center in Hillsdale’s physics department. The four students co-authored two data publications with Dolch in the Astrophysical Journal Supplement Series, and Dolch wrote an additional paper in the Astrophysical Journal Letters.
Halmrast, now a graduate student at University of California Santa Barbara, said the students’ observations were used for the papers’ analyses, and they were only a small part of a very large project. He also had to do a separate project in which he created a data set that observed the Arecibo waves for 24 hours.
“Instead of measurements every two weeks over the course of ten years, it was measured every hundred milliseconds over the course of 24 hours,” Halmrast said. “It’s a completely different data set. It requires different types of analysis so you need to kind of rewrite the whole program, but it’s the same kind of spirit. You’re looking for some sort of wave signal.”
Jessup, now a physics graduate student at Montana State, said he ended up contributing approximately 180 hours to the project as part of his senior thesis.
“You can do it remotely. I basically used my personal computer,” Jessup said. “I connected to the computer down in Arecibo, and basically controlled the telescope remotely from my computer.”
Unfortunately, Arecibo collapsed on Dec. 1, 2020, following a cable breakage the preceding August.
“That was bad but not disastrous,” Dolch said. “But that put additional weight on the remaining cables. In November a cable snapped, leading to a cascading failure of other cables — in other words, to the collapse. Sadly, this happened as the replacement cables were en route on a ship.”
There are several plans for replacement that are being discussed. One is building a successor at the same site because the observatory facility utilizes other smaller instruments, thus lending an already existing infrastructure. Other proposals advocate building new, powerful telescopes elsewhere. But in that case, Dolch noted, the advantage of planetary radar would be lost.
“The main thing that Arecibo did that no other facility in the world (existing or under construction) can do is planetary radar,” Dolch said, explaining that planetary radar is “sending” out radio waves and bouncing them off solar system objects and receiving the reflected signals back. “Much of what we know about Mercury and Venus originally came from Arecibo’s radar work. Additionally, it was really good at tracking near-Earth asteroids. It might be smart to continue to have at least one telescope like that somewhere on Earth!”