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Cosmic mystery solved: The puzzling behavior of a pulsar

Astronomers have cracked a perplexing cosmic mystery with the aid of an impressive observational campaign involving 12 ground and space-based telescopes, including three facilities of the European Southern Observatory (ESO). 

The experts have unraveled the bizarre behavior of a pulsar, a rapidly rotating dead star, which has been switching between two brightness modes almost incessantly – a phenomenon that has, until now, been an enigma. 

Extraordinary cosmic events 

The study revealed that the sudden ejections of matter from the pulsar over extremely short durations are the cause of these peculiar switches.

Study lead author Maria Cristina Baglio is a researcher at New York University Abu Dhabi, affiliated with the Italian National Institute for Astrophysics (INAF).

“We have witnessed extraordinary cosmic events where enormous amounts of matter, similar to cosmic cannonballs, are launched into space within a very brief time span of tens of seconds from a small, dense celestial object rotating at incredibly high speeds,” explained Baglio.

Peculiar type of pulsar

Pulsars are fast-spinning, magnetic, dead stars that project a beam of electromagnetic radiation into space. 

As they rotate, this beam sweeps across the universe – much like a lighthouse beam scanning its surroundings – and is detected by astronomers as it intersects Earth’s line of sight. This results in the star appearing to pulse in brightness when observed from our planet.

PSR J1023+0038, or J1023 for short, is a peculiar type of pulsar exhibiting strange behavior. Situated approximately 4500 light-years away in the Sextans constellation, it orbits another star closely. 

Puzzling behavior 

Over the past decade, the pulsar has been actively extracting matter from its companion, causing it to accumulate in a disc around the pulsar before gradually falling towards it.

Once this accumulation process commenced, the sweeping beam virtually disappeared, and the pulsar began continuously switching between two modes. In the “high” mode, the pulsar emits bright X-rays, ultraviolet, and visible light, while in the “low” mode, it is dimmer at these frequencies and produces more radio waves. 

The pulsar can remain in each mode for several seconds or minutes before transitioning to the other mode in just a few seconds – a phenomenon that has confounded astronomers until now.

“Our unprecedented observing campaign to understand this pulsar’s behavior involved a dozen cutting-edge ground-based and space-borne telescopes,” said co-lead author Francesco Coti Zelati, a researcher at the Institute of Space Sciences in Barcelona.

How the research was conducted 

The project included the ESO’s Very Large Telescope (VLT) and New Technology Telescope (NTT), which detected visible and near-infrared light, as well as the Atacama Large Millimeter/submillimeter Array (ALMA). 

During two nights in June 2021, the telescopes observed the system transitioning over 280 times between its high and low modes.

What the study revealed 

“We have discovered that the mode switching stems from an intricate interplay between the pulsar wind, a flow of high-energy particles blowing away from the pulsar, and matter flowing towards the pulsar,” explained Coti Zelati, who is also affiliated with INAF.

In the low mode, matter flowing towards the pulsar is ejected in a narrow jet perpendicular to the disc. Gradually, this matter accumulates closer to the pulsar, where it is bombarded by the wind emanating from the pulsating star, causing the matter to heat up.

The system then transitions to a high mode, glowing intensely in the X-ray, ultraviolet, and visible light. Eventually, blobs of this heated matter are expelled by the pulsar via the jet. With less hot matter in the disc, the system’s brightness diminishes, reverting back to the low mode.

Further research is needed

While this discovery has demystified the strange behavior of J1023, there is still much to be learned from studying this unique system, and ESO’s telescopes will continue to aid astronomers in observing this unusual pulsar.

Specifically, the ESO’s Extremely Large Telescope (ELT), currently being constructed in Chile, will provide an unparalleled view of J1023’s switching mechanisms.

“The ELT will allow us to gain key insights into how the abundance, distribution, dynamics, and energetics of the inflowing matter around the pulsar are affected by the mode switching behavior,” said Sergio Campana, research director at the INAF Brera Observatory.

The study is published in the journal Astronomy & Astrophysics.

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