For the inaugural time, celestial observers have directly ascertained the manner in which agitated nebulae of ionized plasma situated between stellar bodies refract and obfuscate radio transmissions originating from a remote quasar.
Radio waves originating from the quasar TXS 2005+403 undertake a journey of approximately 10 billion light-years to reach our planet, passing through the Cygnus region, identified as one of the most turbulent and scattering environments within the Milky Way Galaxy. The depiction on the left is an artistic conceptualization showcasing the quasar as it genuinely exists, featuring a luminous accretion disk and jets projecting outward into the Galaxy like a beacon in the darkness. The representation on the right illustrates how the agitated gas distorts the scientists’ perspective of the quasar, in a manner quite analogous to how heat haze emanating from a fire warps our perception of objects situated behind it. Image credit: Melissa Weiss / CfA.
The inter-stellar void within our own Milky Way Galaxy, commonly referred to as the interstellar medium, is characterized by a perpetual state of agitation, replete with formations of ionized gases and free electrons.
When electromagnetic waves in the radio spectrum sourced from distant cosmic entities propagate through this tumultuous material, they undergo deflection and distortion, mirroring the phenomenon of heat haze rising from a fire, which distorts our visual perception of objects located beyond it.
While such distortions have historically provided astronomers with the means to infer the presence of turbulence, a comprehensive understanding of its intricate structure has, until this juncture, remained elusive.
In an endeavor to quantify this turbulence, Alexander Plavin, an astronomer affiliated with the Harvard & Smithsonian Center for Astrophysics, alongside his research associates, focused their observational efforts on a celestial object designated as the quasar TXS 2005+403.
This highly luminous radio source is fueled by the gravitational activity of a supermassive black hole situated at an approximate distance of 10 billion light-years, within the confines of the Cygnus constellation.
As the radio emissions from the quasar traverse their trajectory towards Earth, they pass through the Cygnus region, a locale renowned for its extreme turbulence and significant scattering properties within the Milky Way, consequently causing the radio waves to be deviated and distorted.
“A substantial proportion of what we observe in the radio data originates not from the quasar itself, but rather from the scattering effect induced by the turbulent conditions prevalent in this particular sector of the Milky Way,” stated Dr. Plavin.
“It is precisely this scattering phenomenon and the resultant distortions that furnish us with the capability to investigate the turbulence and thereby enhance our comprehension and inference of its underlying structure.”
To gain a more granular insight into the effects exerted by turbulence on the radio light emanating from TXS 2005+403, the astronomical team meticulously analyzed a compilation of observational data spanning nearly a decade, sourced from the Very Long Baseline Array (VLBA) operated by the National Science Foundation (NSF).
Their initial expectation was that as the radio waves from the quasar passed through the Milky Way, they would diffuse into an indistinct blur and gradually dissipate.
Contrary to this expectation, they discerned persistent, discernible patterns, manifesting as structured, fragmented distortions within the light, which could only be attributed to the influence of turbulence.
“The most distantly situated pairs of telescopes should not have resolved an image of the quasar; however, to our astonishment, they clearly detected its signal, a faint luminosity,” Dr. Plavin elaborated.
“This observation cannot be explained by simple blurring or by the intrinsic properties of the quasar itself; rather, its behavior aligns perfectly with the predicted characteristics of turbulence, thus confirming that we are indeed observing the effects of inter-stellar turbulence.”
“The scattering characteristics along this particular line of sight through the Galaxy remain consistently discernible over extended periods.”
A comprehensive publication detailing these groundbreaking findings has been issued in the Astrophysical Journal Letters.
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A.V. Plavin et al. 2026. Direct Very Long Baseline Interferometry Detection of Interstellar Turbulence Imprint on a Quasar: TXS 2005+403. ApJL 1003, L4; doi: 10.3847/2041-8213/ae60f4
