Nov. 27 () –
Data from the old Arecibo Observatory indicate patterns that show how pulsar signals change through the interstellar medium (ISM), the gas and dust that fills the space between stars.
A team of university researchers at the Penn State branch of the student club Press Search Collaboratory measured the scintillation bandwidths of 23 pulsars, including new data from six pulsars that had not been previously studied.
Published in The Astrophysical Journalthe results showed that, in almost all cases, the measured bandwidths were greater than the predictions of widely used galaxy models, which highlights the need to update current density models of the interstellar medium.
“This work demonstrates the value of large archived data sets,” said in a statement Sofia Sheikh, researcher at the SETI Institute and lead author. “Even years after the Arecibo Observatory collapse, its data continues to reveal critical information that can advance our understanding of the galaxy and improve our ability to study phenomena such as gravitational waves.”
When radio light from a pulsar travels through the interstellar medium, it becomes distorted in a process known as “diffractive interstellar scintillation” (DISS, for its acronym in English). The same physics that causes light to refract into patterns on the bottom of a swimming pool or stars to twinkle in the night sky also causes DISS. Instead of water in a pool or air in the atmosphere, DISS occurs when clouds of charged particles in space cause light from a pulsar to “twinkle” over time and frequency.
Collaborations such as the NANOGrav Center for Frontiers in Physics use pulsars to study the background of gravitational waves, which can help researchers understand the early Universe and the prevalence of gravitational wave sources such as supermassive black hole binary systems. Pulsar timing measurements must be extremely precise to correctly measure the gravitational wave background. The results of this study will help better model the distortions caused by DISS, increasing the accuracy of pulsar timing measurements from projects like NANOGrav.
The study found that models that incorporate galactic structures, such as spiral arms, tend to fit DISS data better despite the challenge of accurately modeling the structure of the Milky Way. Additionally, the study showed that the models more accurately predicted the bandwidths of the pulsars that were used in their development, while the predictions of the newly discovered pulsars were worse. This suggests limitations that reinforce the need for continuous updates of galactic structure models.
This pilot study, part of the Arecibo AO327 survey, serves as a basis for future research on pulsar scintillation and gravitational waves. By expanding the pilot study to more recently discovered pulsars in the AO327 data set in the future, the team hopes to further improve density models of the interstellar medium for collaborations observing pulsar timing ensembles like NANOGrav.
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