Astronomers solve mystery of spinning dead star

30 Aug 2023

Image: M. Kornmesser/ESO

ESO telescopes helped a team of scientists unravel the mystery around a pulsar that has been switching between two modes of energy emission in seconds.

Around 4,500 light years away from Earth, nestled in the Sextans constellation lies a super-fast-spinning dead star – known as a pulsar – whose erratic behaviour has long eluded the understanding of astronomers. Now, thanks to a complex interplay of a dozen different telescopes across the Earth and space, this mystery has been solved.

Some of the most enigmatic objects in the universe, pulsars are highly magnetic neutron stars (the collapsed cores of supermassive stars) that emit energetic beams of electromagnetic radiation from each of their magnetic poles.

One particular pulsar, known to astronomers as J1023, has been observed for a while now and is known for its inexplicable behaviour: it switches between two brightness modes almost constantly.

J1023 closely orbits another star and has been, over the past decade, actively “pulling matter off” this companion, which accumulates in a disc around the pulsar and slowly falls towards it. The European Southern Observatory (ESO) has a video that shows this phenomenon.

When the pulsar is in its ‘high’ mode, it gives off bright X-rays, ultraviolet rays and visible light. But when in the ‘low’ mode, the pulsar’s emissions get dimmer with more radio waves. The switch between the two modes can take place in seconds.

Dr Maria Cristina Baglio, a researcher at New York University Abu Dhabi, affiliated with the Italian National Institute for Astrophysics (INAF), says this is an “extraordinary cosmic event”. She is a lead author of a paper on the study published today (30 August) in Astronomy & Astrophysics.

“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,” Baglio said.

Thanks to the study, which used three different ESO telescopes for the observations, we now know that sudden ejections of matter from the pulsar over very short periods are responsible for the peculiar switches.

The team used the ESO’s Very Large Telescope and New Technology Telescope to detect visible and near-infrared light. It also used the ESO partner Atacama Large Millimeter/submillimeter Array, popularly known as ALMA, for its observations.

Over two nights in June 2021, astronomers observed the system make over 280 switches between its high and low modes.

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

“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,” added Coti Zelati, who is also affiliated with the INAF.

While the mystery behind the J1023 pulsar is now solved, the ESO says astronomers have much to learn about the unique object and its behaviour. It hopes the Extremely Large Telescope (ELT) currently being built in Chile will help them delve deeper into this.

“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 behaviour,” said Dr Sergio Campana, research director at INAF and co-author of the study.

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Vish Gain is a journalist with Silicon Republic