ESO Telescopes Helped to Solve Pulsar Mystery

Astronomers have used 12 telescopes, including three from the European Southern Observatory (ESO), to observe a pulsar that switches between two brightness modes almost constantly. The team found that sudden ejections of matter from the pulsar are responsible for the peculiar switches.

This artist's impression shows the pulsar PSR J1023+0038 stealing gas from its companion star. This gas accumulates in a disk around the pulsar, slowly falls towards it, and is eventually expelled in a narrow jet. In addition, there is a wind of particles blowing away from the pulsar, represented here by a cloud of very small dots. This wind clashes with the infalling gas, heating it up and making the system glow brightly in X-rays and ultraviolet and visible light. Eventually, blobs of this hot gas are expelled along the jet, and the pulsar returns to the initial, fainter state, repeating the cycle. This pulsar has been observed to switch incessantly between these two states every few seconds or minutes. Credit: ESO/M. Kornmesser

The pulsar, called PSR J1023+0038, is located about 4,500 light-years away in the Sextans constellation. It is a special type of pulsar called a millisecond pulsar, which means that it rotates very quickly, once every 2.4 milliseconds.

Millisecond pulsars are formed when a neutron star, the collapsed core of a star, accretes matter from a companion star. In the case of PSR J1023+0038, the companion star is a white dwarf, a dense star that has exhausted its nuclear fuel.

As the neutron star rotates, it emits a beam of radio waves that sweeps across the sky. When this beam passes over Earth, we see a bright pulse of radio waves.

However, in recent years, PSR J1023+0038 has been observed to switch between two brightness modes. In the "high" mode, the pulsar emits bright X-rays, ultraviolet, and visible light. In the "low" mode, it is dimmer at these frequencies and emits more radio waves.

The team of astronomers used ESO's Very Large Telescope (VLT), New Technology Telescope (NTT), and Atacama Large Millimeter/submillimeter Array (ALMA) to observe PSR J1023+0038 over two nights in June 2021. They observed the system make over 280 switches between its high and low modes.

The team's analysis of the data showed that the mode switching is caused by sudden ejections of matter from the pulsar. These ejections are thought to be caused by the interaction between the pulsar's magnetic field and the matter flowing from the companion star.

The matter ejected from the pulsar forms a disk around the neutron star. As the disk accumulates, it heats up and emits X-rays, ultraviolet, and visible light. Eventually, the disk becomes unstable and the matter is ejected again, causing the pulsar to switch to its low mode.

This discovery is a major step forward in our understanding of pulsars. It also provides new insights into the physics of neutron stars and their interactions with their companion stars.

The team's findings were published in the journal Astronomy & Astrophysics.

Journal Information: M.C. Baglio et al, Matter ejections behind the highs and lows of the transitional millisecond pulsar PSRJ1023+0038, Astronomy & Astrophysics (2023). DOI: 10.1051/0004-6361/202346418