An international team of astronomers have discovered the slowest-spinning radio pulsar yet known. The neutron star spins around only once every 23.5 seconds and is a challenge for theory to explain. The researchers, including astronomers at the University of Manchester, ASTRON and the University of Amsterdam, carried out their observations with the LOFAR telescope, whose core is located in the Netherlands. Their findings will soon appear in the Astrophysical Journal.

Published by the editorial team, 23 October 2018

Pulsars are rapidly rotating neutron stars that produce electromagnetic radiation in beams that emanate from their magnetic poles. These “cosmic lighthouses” are born when a massive star explodes in a supernova. Thereafter, a super-dense ball of material is left behind – rapidly spinning, and with a diameter of only about 20 kilometers. The fastest-spinning pulsar rotates once each 1.4 milliseconds. Until now, the slowest-spinning pulsar known had a period of 8.5 seconds. Now researchers have discovered a much slower, 23.5-second, pulsar, which is located in the constellation Cassiopeia.

“It is incredible to think that this pulsar spins more than 15.000 times more slowly than the fastest spinning pulsar known.” said Chia Min Tan a PhD Student at the University of Manchester who discovered the pulsar. “We hope that there are more to be found with LOFAR”.

The astronomers discovered this new pulsar during the LOFAR Tied-Array All-Sky Survey. This survey is searching for pulsars in the Northern sky. Each survey snapshot of the sky lasts for one hour. This is much longer compared to previous surveys, and gave the sensitivity needed to discover this surprising pulsar.

Not only did the astronomers 'hear' the regular ticks of the pulsar signal, they could also 'see' the pulsar in LOFAR’s imaging survey. Co-author Cees Bassa (ASTRON): “This pulsar spins so remarkably slowly that we could see it blinking on and off in our LOFAR radio images. With faster pulsars that’s not possible.”

 Artist’s conception of the newly discovered 23.5-second pulsar. Radio pulses originating from a source in the constellation Cassiopeia are seen travelling towards the core of the LOFAR telescope array. This source is a highly magnetised radio pulsar, shown in the inset image. The pulses and sky image are derived from the actual LOFAR data. Credit: Danielle Futselaar and ASTRON.

The pulsar is approximately 14 million years old, but still has a strong magnetic field. Co-author Jason Hessels (ASTRON and University of Amsterdam): “This pulsar was completely unexpected. We’re still a bit shocked that a pulsar can spin so slowly and still create radio pulses. Apparently radio pulsars can be slower than we expected. This challenges and informs our theories for how pulsars shine.”

Moving forward, the astronomers are continuing their LOFAR survey for new pulsars. They are also planning to observe their new find with the XMM-Newton space telescope. This telescope is designed to detect X-rays. If the super-slow pulsar is detected as a source of X-rays, then this will give important insights into its history and origin.

Reference

LOFAR discovery of a 23.5-second radio pulsar. By: C.M. Tan (1), C.G. Bassa (2), S. Cooper (1), T.J. Dijkema (2), P. Esposito (3,4), J.W.T. Hessels (2,3), V.I. Kondratiev (2,5), M. Kramer (6,1), D. Michilli (3,2), S. Sanidas (1), T.W. Shimwell (2), B.W. Stappers (1), J. van Leeuwen (2,3), I. Cognard (7,8), J.-M. Grießmeier (7,8), A. Karastergiou (9,10,11), E.F. Keane (12), C. Sobey (13,14), P. Weltevrede (1). (preprint)

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