Multiband ALMA polarimetry of the jet base and kiloparsec-scale jet of 3C 273: A multicomponent Faraday structure in the nucleus

Polarization observations at millimeter wavelengths can be used to study magnetized plasma in jets launched by supermassive black holes. The new analysis still awaits peer review, but it already lays out the central claim clearly.

This matters because astrophysics becomes persuasive only when an observed signal can be tied to a physically defensible explanation. Compact objects such as neutron stars and black holes are natural laboratories for extreme physics, but the distance and complexity of these systems make interpretation difficult without multi-wavelength coverage and careful modeling. A detection without a mechanism is only half a result. the other half comes from showing that the signal fits quantitatively inside a coherent physical picture rather than merely being consistent with a broad family of models. We used multiband Atacama Large Millimeter Array (ALMA) data to study the polarization structure of both the nucleus and the kiloparsec-scale jet of the archetypal quasar 3C 273. We also produced total intensity and polarization maps of the kiloparsec-scale jet to study the evolution of the magnetic field structure along and across the jet.

The high RM is comparable to previous ALMA observations at 1.3 mm, although we found clear evidence of variability when compared to previous single-band ALMA studies, highlighting. On kiloparsec scales, the millimeter polarization structure closely resembled that observed at centimeter wavelengths, revealing a complex magnetic field configuration around the.

Our results indicate a multicomponent, time-variable Faraday screen in the nuclear region of 3C 273 that is likely associated with a dense, magnetized environment close to the jet. Future spatially resolved millimeter polarimetry with the Event Horizon Telescope will be crucial to disentangling these components and directly localizing the high-RM emission.

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The broader interest lies in turning an observational clue into something that can be weighed against competing models of the underlying physics. Astrophysics does not have the luxury of controlled experiments; everything is inferred from radiation that traveled across cosmic distances under conditions that cannot be reproduced in a terrestrial laboratory. This makes the interpretation chain longer and more uncertain than in bench science, but it also means that a well-constrained measurement of an extreme object carries theoretical information that no earthbound experiment can provide.

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Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to see whether independent datasets and physical modeling converge on the same interpretation. Multi-wavelength follow-up, combining X-ray, radio and optical data where possible, is typically what separates a compelling detection from a robust physical characterization. In high-energy astrophysics, results that initially looked definitive have been revised when data from a second messenger arrived; the current result should be read with that history in mind. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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