Dr. Sofia Sheikh, a researcher from the SETI Institute, has spearheaded a study that provides a fresh perspective on pulsar signals. Pulsars are rapidly spinning remnants of massive stars, and their signals often distort while traversing through the cosmos.
This research, published in The Astrophysical Journal, was conducted by a group of dedicated undergraduate researchers over several years at Penn State’s branch of the Pulsar Search Collaboratory student club. Maura McLaughlin, the Chair and Eberly Distinguished Professor of Physics and Astronomy at West Virginia University, initially established the Collaboratory to involve high school and undergraduate students in pulsar research. She also assisted in providing access to the data necessary for this study.
Through the analysis of archival data from the Arecibo Observatory, the team identified patterns that elucidate how pulsar signals alter while journeying through the interstellar medium (ISM) – the mix of gas and dust filling the space between stars. The team examined the scintillation bandwidths of 23 pulsars, including six not previously studied, and discovered that the measured bandwidths surpassed the predictions of commonly used galactic models, indicating a need for model updates.
Dr. Sheikh, the leading author of the study, emphasized the significance of large, archived datasets, saying, “Even years after the Arecibo Observatory’s collapse, its data continues to unlock critical information that can advance our understanding of the galaxy and enhance our ability to study phenomena like gravitational waves.”
The phenomenon known as “diffractive interstellar scintillation” (DISS) causes the distortion of radio light from pulsars as it travels through the ISM. This process is similar to the refraction of light in water that creates patterns at the bottom of a swimming pool or causes stars to twinkle in the night sky. However, in the case of DISS, it is the clouds of charged particles in space that cause pulsar light to “twinkle.”
Projects like the NANOGrav Physics Frontiers Center use pulsars to study the gravitational wave background, aiding in understanding the early Universe and the prevalence of gravitational-wave sources such as supermassive black-hole binaries. Precise pulsar timing measurements are crucial for correct readings of the gravitational wave background. The discoveries from this study will help refine models of the distortions caused by DISS, thereby improving the precision of pulsar timing measurements for projects like NANOGrav.
The study also found that models incorporating galactic structures such as spiral arms were more consistent with the DISS data, despite the difficulty of accurately modeling the structure of the Milky Way. There were also limitations observed in the models, as they could most accurately predict the bandwidths of the pulsars they were designed to study, but were less accurate for newly discovered pulsars. This suggests a need for ongoing updates to galactic structure models.
The study serves as a base for future research on pulsar scintillation and gravitational waves, as the researchers plan to expand their study to include more recently discovered pulsars. This will further refine the ISM density models, which is beneficial for projects that observe pulsar timing arrays like NANOGrav.
The research was a collaborative effort between authors at the SETI Institute, Penn State, and the NANOGrav Group at West Virginia University, including SETI Institute researcher Michael Lam and former SETI Institute researcher Grayce Brown.
