Andromeda is one of the closest galaxies to the Milky Way and has been a target for detailed observation for decades. And now those efforts have led to the discovery of the most distant pulsar yet.

The discovery was possible thanks to ESA’s XMM-Newton space telescope. The object spins on itself every 1.2 seconds, and it has a companion that it orbits every 1.3 days. 

The object is the second extragalactic pulsar ever discovered. The first one was discovered last November in the Large Magellanic Cloud. This discovery is important because astronomers use Andromeda as a model for the Milky Way, given its shape and proximity, Andromeda is like the big sister of our own galaxy.

“We were expecting to detect periodic signals among the brightest X-ray objects in Andromeda, in line with what we already found during the 1960s and 1970s in our own Galaxy,” Gian Luca Israel, one of the authors of the paper describing the results, said in a statement.

“But persistent, bright X-ray pulsars like this are still somewhat peculiar, so it was not completely a sure thing we would find one in Andromeda.”

^{Here we can see the pulsar identified in the galaxy.  ESA/Herschel/PACS/SPIRE/J.Fritz, U.Gent/XMM-Newton/EPIC/W. Pietsch, MPE}

The findings are published in the Monthly Notices Letters of The Royal Astronomical Society, but the team is unsure about many parameters of the system as they are basing their analysis on just two measurements.

“It could be what we call a ‘peculiar low-mass X-ray binary pulsar’ – in which the companion star is less massive than our Sun – or alternatively an intermediate-mass binary system, with a companion of about two solar masses,” said lead author Paolo Esposito.

“We need to acquire more observations of the pulsar and its companion to help determine which scenario is more likely.”

Pulsars are a special class of pulsating neutron stars, highly magnetized and spinning very quickly. They are the leftovers of certain supernova explosions. They emit a beam of charged particles along their magnetic field, which tends to be misaligned with their rotation axis, hence why they appear to be pulsating.

ESA’s XMM-Newton project scientist Norbert Schartel concluded, “We’re in a better position now to uncover more objects like this in Andromeda, both with XMM-Newton and with future missions such as ESA’s next-generation high-energy observatory, Athena.”