New Light on Transitional Millisecond Pulsars: Multi-Wavelength Study Unveils Complex Emission Mechanics in PSR J1023+0038

PSR J1023+0038

In a groundbreaking international collaboration, physicists from the University of Oxford, in concert with researchers from institutions across the globe, have uncovered compelling new insights into the behavior of a rare astronomical object: a transitional millisecond pulsar, specifically PSR J1023+0038. Their findings, published in The Astrophysical Journal Letters and Astronomy & Astrophysics, present the most detailed multi-wavelength polarimetric study to date of such a system—offering unprecedented evidence of complex emission mechanisms and dynamic astrophysical processes.

Transitional millisecond pulsars (tMSPs) like PSR J1023+0038 are neutron stars in binary systems that exhibit a rare and dramatic dual nature. They oscillate between a radio-loud pulsar state, where the neutron star’s magnetic field accelerates particles and emits periodic radio pulses, and an accreting state, during which the star draws in matter from a companion star, releasing erratic, multi-band radiation. With only a few known tMSPs in existence, PSR J1023+0038 stands out as the archetype for such rare systems.

Polarised Light from Colliding Winds

Led by Dr. Maria Cristina Baglio of Italy’s INAF-Brera Observatory, the study involved a multi-wavelength polarimetric campaign combining data from NASA’s Imaging X-ray Polarimetry Explorer (IXPE), the European Southern Observatory’s Very Large Telescope (VLT), and the Karl G. Jansky Very Large Array (VLA) in the United States.

Oxford physicists Dr Andrew Hughes and Dr Francesco Carotenuto played a key role in the interpretation of this data. Remarkably, IXPE recorded an X-ray polarisation of around 12%, while VLT measurements revealed a 1% optical polarisation. Most strikingly, both bands exhibited aligned polarisation angles, despite the vast difference in their wavelengths. This coherence suggests a common physical origin of the observed emissions.

Rather than originating from hot spots on the surface of the neutron star, as is the case in many pulsars, the researchers propose that the emissions result from synchrotron radiation—high-energy photons produced when relativistic particles are accelerated in strong magnetic fields. In PSR J1023+0038, this radiation likely comes from the collision region between the pulsar wind and the inner edge of the accretion disk—a turbulent, high-energy interface rarely observed so clearly.

“Transitional millisecond pulsars are natural laboratories for studying how neutron stars evolve in binary systems,” said Dr. Baglio. “Our observations of PSR J1023+0038 reveal a remarkably consistent polarisation orientation spanning from optical light to X-rays. The alignment across these bands strongly suggests a single, coherent physical process driving the pulsar’s broadband emission.”

A Tale of Two Emission Zones

In contrast to the X-ray and optical signals, no detectable polarisation was found in the radio band, according to the Oxford team’s analysis of VLA data. While this might seem insignificant at first glance, it provided a key clue.

“The lack of radio polarisation in our data provides a strong clue,” explained Dr. Andrew Hughes. “It supports the idea that, while the X-ray and optical emission originates from colliding winds near the pulsar, the radio emission arises from a separate, jetted outflow of relativistic particles. This points to the existence of not one, but two distinct high-energy particle acceleration zones within the system.”

This dual-region scenario challenges conventional understandings of pulsar emission and suggests a more intricate geometry than previously modeled. The presence of a jetted outflow alongside the wind-disk collision zone opens new avenues for research into relativistic jet production in stellar-mass systems—phenomena usually associated with black holes or active galactic nuclei.

Coordinated Campaigns Unlock New Astrophysics

Dr. Francesco Carotenuto emphasized the value of synchronised, cross-spectrum observations in illuminating such complex astrophysical processes.

“Our study highlights the critical role of coordinated, multi-band campaigns – especially those incorporating sensitive radio data – in unlocking the physics of these exotic stellar remnants,” said Dr. Carotenuto.

The importance of PSR J1023+0038 as a template for tMSP behavior remains a subject for further investigation. While a couple of other known pulsars fall within this transitional category and more are under consideration, questions remain: Is this system representative of all tMSPs? Or is it a unique object, even among its rare class?

The findings mark a significant step forward in the field of high-energy astrophysics, particularly in our understanding of how neutron stars evolve, interact with their environment, and produce complex emissions. With future campaigns likely to incorporate next-generation telescopes and even more refined polarimetric tools, researchers hope to construct a more unified model of particle acceleration, magnetospheric dynamics, and accretion processes across the broader population of compact binary systems.

As Dr. Baglio and her collaborators demonstrate, the frontier of pulsar science lies in interdisciplinary, multinational collaboration, leveraging the full electromagnetic spectrum to unravel the mysteries of the universe’s most extreme objects.