Deciphering Pulsar PSR J1023+0038’s Mysterious Brightness Shifts

A team of astronomers has unraveled the peculiar behavior of the pulsar PSR J1023+0038, employing a dozen telescopes, including those operated by the European Southern Observatory (ESO). This particular pulsar, known for its rapid alternation between two distinct brightness modes, undergoes sudden bursts of matter ejection, leading to these intriguing shifts. This groundbreaking discovery, achieved through comprehensive observations and meticulous analysis, significantly advances our comprehension of pulsar dynamics and lays the foundation for future revelations with cutting-edge telescopes like ESO’s Extremely Large Telescope.

In an extensive astronomical investigation utilizing a dozen telescopes, both terrestrial and orbital, and featuring the participation of three European Southern Observatory (ESO) facilities, scientists have uncovered the enigmatic conduct of a pulsar—an immensely fast-spinning deceased star. This celestial entity is distinguished by its perpetual oscillation between two distinct brightness modes, a phenomenon that had hitherto confounded researchers. However, astronomers have now determined that abrupt expulsions of matter from the pulsar, transpiring within brief time intervals, are the driving force behind these peculiar transitions.

Maria Cristina Baglio, a researcher affiliated with New York University Abu Dhabi and the Italian National Institute for Astrophysics (INAF), and the lead author of the recently published article in the journal Astronomy & Astrophysics, elucidates, “We have witnessed extraordinary cosmic events where enormous amounts of matter, akin to cosmic cannonballs, are propelled into space within mere tens of seconds emanating from a diminutive, dense celestial object rotating at incredibly high speeds.”

Pulsars, celestial enigmas in their own right, are rapid-rotating, magnetic remnants of stars that emit beams of electromagnetic radiation into the cosmos. As these pulsars rotate, their emitted beams sweep across the universe, akin to a lighthouse beam scanning its surroundings. These beams, when intersecting the line of sight to Earth, manifest as pulsations in brightness observable by astronomers.

Located approximately 4500 light-years away in the Sextans constellation, PSR J1023+0038, or J1023 for brevity, is a distinctive type of pulsar. This particular pulsar is engaged in a close orbit with another stellar companion. Over the past decade, J1023 has been actively accreting matter from its companion, resulting in the formation of a circumstellar disc around the pulsar, from which matter gradually descends toward it.

This intricate process of matter accumulation has led to the vanishing of the sweeping beam and the onset of J1023’s continual oscillation between two modes. In its ‘high’ mode, the pulsar emits intense X-rays, ultraviolet, and visible light emissions, while in the ‘low’ mode, it exhibits diminished luminosity in these spectral regions, accompanied by increased radio wave emissions. J1023 can persist in each mode for several seconds to minutes before swiftly transitioning to the alternative mode in mere seconds. This baffling behavior has been a source of puzzlement for astronomers until now.

The comprehensive telescopic campaign that shed light on this pulsar’s conduct entailed the deployment of a dozen state-of-the-art ground-based and space-based telescopes. Francesco Coti Zelati, a researcher at the Institute of Space Sciences, Barcelona, Spain, and co-lead author of the research paper, underscores, “Our unprecedented observing campaign to comprehend this pulsar’s behavior involved a dozen cutting-edge ground-based and space-borne telescopes.” Notably, the campaign encompassed ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT), which captured visible and near-infrared light, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), where ESO played a collaborative role. During two nights in June 2021, the researchers recorded over 280 transitions between the pulsar’s high and low modes.

Coti Zelati further explains, “We have ascertained that the mode shifts are a consequence of a complex interplay between the pulsar’s wind—a stream of high-energy particles radiating away from the pulsar—and the inflowing matter directed toward the pulsar.”

In the ‘low’ mode, the inflowing matter toward the pulsar is expelled in a narrow jet perpendicular to the circumstellar disc. As this matter progressively accumulates closer to the pulsar, it encounters the wind emanating from the pulsar, resulting in its heating. This intricate interaction propels the system into a ‘high’ mode, emitting radiant X-rays, ultraviolet, and visible light. Ultimately, blobs of this heated material are expelled by the pulsar through the jet. With reduced quantities of hot matter in the disc, the system’s luminosity diminishes, triggering a transition back into the ‘low’ mode.

While this discovery has demystified the perplexing behavior of J1023, there remains much to be learned from the study of this unique celestial system. ESO’s telescopes will continue to play a pivotal role in enabling astronomers to scrutinize this peculiar pulsar. Notably, the forthcoming Extremely Large Telescope (ELT), currently under construction in Chile, holds the promise of providing unprecedented insights into the mechanisms governing J1023’s mode transitions.

Sergio Campana, Research Director at the INAF Brera Observatory and a coauthor of the study, concludes, “The ELT will enable us to gain essential insights into how the abundance, distribution, dynamics, and energetics of the inflowing matter around the pulsar are influenced by the mode-switching behavior.”

Reference: “Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038” by M. C. Baglio, F. Coti Zelati, S. Campana, G. Busquet, P. D’Avanzo, S. Giarratana, M. Giroletti, F. Ambrosino, S. Crespi, A. Miraval Zanon, X. Hou, D. Li, J. Li, P. Wang, D. M. Russell, D. F. Torres, K. Alabarta, P. Casella, S. Covino, D. M. Bramich, D. de Martino, M. Méndez, S. E. Motta, A. Papitto, P. Saikia and F. Vincentelli, 30 August 2023, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202346418

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More about Pulsar Behavior

• European Southern Observatory (ESO)
• Astronomy & Astrophysics Journal
• PSR J1023+0038 – Wikipedia
• Pulsars – NASA