The millisecond pulsar PSR J1023+0038 is known to switch between two brightness modes almost constantly, something that until now has been an enigma.
This artist’s impression shows the millisecond pulsar PSR J1023+0038 stealing gas from its companion star. Image credit: ESO / M. Kornmesser.
PSR J1023+0038 is a 1.69 ms radio pulsar located about 4,500 light-years away in the constellation of Sextans.
Discovered in 2007, it orbits a low-mass (0.2 solar masses) companion star with a period of only 4.75 hours.
Over the past decade, PSR J1023+0038 has been actively pulling matter off this companion, which accumulates in an accretion disk around the pulsar and slowly falls towards it.
Since this process of accumulating matter began, the sweeping beam virtually vanished and the pulsar started incessantly switching between two modes.
In the ‘high’ mode, the pulsar gives off bright X-rays, ultraviolet and visible light, while in the ‘low’ mode it’s dimmer at these frequencies and emits more radio waves.
The pulsar can stay in each mode for several seconds or minutes, and then switch to the other mode in just a few seconds. This switching has thus far puzzled astronomers.
“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,” said Dr. Maria Cristina Baglio, an astronomer at New York University Abu Dhabi and the Italian National Institute for Astrophysics.
Dr. Baglio and her colleagues carried out the most extensive multi-wavelength campaign ever conducted on the transitional pulsar, covering from the radio to X-rays.
The campaign involved 12 different telescopes and instruments, including ESA’s XMM-Newton observatory, the NASA/ESA Hubble Space Telescope, the FORS2 instrument on ESO’s Very Large Telescope, the Atacama Large Millimeter/submillimeter Array, NSF’s Karl G. Jansky Very Large Array, and FAST.
Over two nights in June 2021, the astronomers observed over 280 switches between its high and low modes in PSR J1023+0038.
“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,” said Dr. Francesco Coti Zelati, an astronomer at the Institute of Space Sciences in Barcelona and the Italian National Institute for Astrophysics.
In the low mode, matter flowing towards the pulsar is expelled in a narrow jet perpendicular to the disk.
Gradually, this matter accumulates closer and closer to the pulsar and, as this happens, it is hit by the wind blowing from the pulsating star, causing the matter to heat up.
The system is now in a high mode, glowing brightly in the X-ray, ultraviolet and visible light.
Eventually, blobs of this hot matter are removed by the pulsar via the jet.
With less hot matter in the disk, the system glows less brightly, switching back into the low mode.
“Our results show how multi-wavelength campaigns that combine diverse observational techniques provide powerful tools for unraveling the nature of elusive objects such as transitional millisecond pulsars,” the astronomers said.
Their paper was published in the journal Astronomy & Astrophysics.
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M.C. Baglio et al. 2023. Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038. A&A 677, A30; doi: 10.1051/0004-6361/202346418
