February 29, 2024

Mysterious Interstellar Plasma Revealed by Twinkling Pulsars

Artists illustration of a pulsar. Credit: Carl Knox, OzGrav-Swinburne University
Astrophysicists predict that these brief bursts of brightness take place because thick regions of interstellar plasma (the hot gas in between stars) scatter the radio waves given off by the pulsar. A promising opportunity for this is in the scintillation, or “twinkling,” of pulsars.
When a pulsars radio waves are spread by the interstellar plasma, the separate waves produce an interference and interfere pattern on the Earth. The scattering and twinkling happens in little regions of the plasma thanks to the point-like nature of pulsar signals.
The pulsars trajectory still hasnt been identified as it orbits another compact star called a white dwarf in a face-on orbit, and astronomers do not have alternative approaches to determine it in this circumstance. Scintillation arcs serve a double function: their curvatures are associated to the pulsars speed, as well as the distance to the plasma and the pulsar. How the pulsars velocity modifications as it orbits depends on the orbits orientation in space.

Astrophysicists forecast that these short bursts of brightness occur because dense regions of interstellar plasma (the hot gas between stars) spread the radio waves produced by the pulsar. When a pulsars radio waves are spread by the interstellar plasma, the separate waves interfere and develop an interference pattern on the Earth. The scattering and twinkling happens in little areas of the plasma thanks to the point-like nature of pulsar signals. Scintillation arcs serve a double purpose: their curvatures are related to the pulsars velocity, as well as the distance to the plasma and the pulsar. The question, for that reason, stays open: what is the source of the plasma that spreads the pulsars radiation?

The measurements we acquired for the orbit of pulsar J1603-7202 are a significant enhancement compared to previous analyses. We determined the range to the plasma and showed that it was about three-quarters of the distance to the pulsar, from Earth. The question, for that reason, stays open: what is the source of the plasma that scatters the pulsars radiation?
Lastly, utilizing our orbit measurement, we are able to estimate the mass of J1603-7202s orbital buddy. It was determined to be about half the mass of the Sun. When thought about alongside the highly circular orbit of J160-7202, this implies the companion is likely a stellar remnant made up of carbon and oxygen– a rarer discover around a pulsar than the more typical helium-based remnants.
As we now possess a near-complete model of the orbit, its currently possible to change scintillation observations of J1603-7202 into on-sky spread images and map the interstellar plasma at Solar System scales. Developing pictures of the physical structures that trigger severe scattering of radio waves might provide us a better understanding of how such thick areas form and of the function the interstellar plasma plays in the advancement of galaxies.
Written by PhD trainee Kris Walker (ICRAR-UWA) and Dr. Daniel Reardon (OzGrav-Swinburne University).
Reference: “Orbital Dynamics and Extreme Scattering Event Properties from Long-term Scintillation Observations of PSR J1603 − 7202” by Kris Walker, Daniel J. Reardon, Eric Thrane and Rory Smith, 28 June 2022, The Astrophysical Journal.DOI: 10.3847/ 1538-4357/ ac69c6.