On the Pulse of Discovery

editorial On the pulse of discovery

What started 50 years ago as a ‘smudge’ on paper has fourished into a fundamental feld of astrophysics replete with unexpected applications and exciting discoveries. To celebrate the discovery of pulsars, we look at the past, present and future of pulsar astrophysics.

ifty years ago this month, Jocelyn Bell Taylor and Russell Hulse in 1975 of a pulsar Burnell (pictured) had already seen in a binary system with another neutron Fthe recurring blips on her hundreds- star. The orbit of the pulsar was observed of-metres-long chart paper that was being to shrink in the exact way that Einstein’s churned out by the newly minted 4-acre- general theory of relativity predicted if the array radio telescope at Cambridge, UK. system was emitting gravitational waves Together with her PhD advisor, Antony (and brought in another Nobel Prize Hewish, they were hard at work trying to for the pulsar field). Today, we are not understand their nature and the source that only detecting pulsars and neutron stars could have generated them. The study of what from space (see the Mission Control by we now know as pulsars has developed into Keith Gendreau and Zaven Arzoumanian), a vibrant field of research that touches upon but a network of pulsars is poised to almost all areas of astrophysics and beyond: become the largest gravitational-wave from stellar astronomy, to the physics of detector at our disposal (see the Article condensed matter, to gravitational waves and by Chiara Mingarelli and collaborators the very fabric of our Universe. In this and the Comment by Andrea Lommen). focus issue we bring together some of the Gravitational-wave detection aside, pulsars most exciting pulsar science and reflect on are now being used to probe the most the future directions of the field. fundamental properties of spacetime The discovery of pulsars required the (see the Comment by Kuo Liu and Ralph attentiveness of a self-professed imposter- Eatough) and of condensed matter. Some syndrome-suffering PhD student (whose of these topics were discussed recently at contribution was disappointingly snubbed the IAU Symposium 337 on the occasion when the Nobel Prize committee came of the pulsar discovery (summarized in the knocking), the prowess of a novel telescope Meeting Report by Nanda Rea) that took Credit: Daily Herald Archive / SSPL / Getty Images probing new parts of parameter space and place on the grounds of the Jodrell Bank of course the collective thinking of our Observatory — itself celebrating 60 years of community to figure out what these blips discoveries in pulsar research and beyond probing a new niche of the phase space, were (see the Perspective by Jocelyn Bell (see the Perspective by Andrew Lyne serendipitous discoveries are bound to Burnell). Pulsars are the end products of and Ian Morison). happen, as long as we have vigilance and massive stellar evolution, compact stars The discovery of pulsars was not only an open mind to identify them as such made primarily out of neutrons, often fortuitous but more importantly it was — attributes Bell Burnell and Hewish spinning at dizzying speeds (up to ~0.24 serendipitous. When the Cambridge did have. Nowadays, however, not many times the speed of light) and showing a radio astronomy group decided to build astronomers sift through piles of chart precision in their rotation, for the most their telescope they had quasars in mind. papers to identify signals. They instead stable pulsars, rivalling that of atomic This discovery is reminiscent of another build algorithms to do the sifting for them. clocks (10–21 s). They also have prodigious discovery that heralded the era of precision How does one build intuitiveness into an magnetic fields, which, when combined with cosmology — in 1964 Arno Penzias and algorithm, how does one teach algorithms their rotation, lead to the emission of the Robert Wilson inadvertently detected the to identify what is practically unknown? pulses we observe. echo from the Big Bang. Fifty years later, the Unsupervised clustering from deep- Neutron stars were first predicted by golden age of serendipitous discovery seems learning neural networks may be a step in Walter Baade and Fritz Zwicky in 1934 to be well and truly over. We find ourselves the right direction but this conundrum is but the idea of a rotating neutron star instead in the age of certainty, calculated something that deserves our community’s with a strong magnetic field only arose in risks, assured returns and zero-sum undivided attention. Data from facilities like 1967, championed by Franco Pacini, and science (see the Correspondence by Maura the Square Kilometre Array will soon be independently in 1968 by Thomas Gold, McLaughlin). Have our telescopes become pouring into our servers and we need who even made the connection between too expensive and our experiments too to be ready. Who knows what 'pulsars' such stars and the discovery reported by involved to allow room for the unexpected? may be hiding there? ❐ Hewish and Bell in the same year. The In some sense, whenever a truly new importance of this discovery for astrophysics instrument is built (the Laser Interferometer and physics in general was perhaps made Gravitational-wave Observatory Published online: 1 December 2017 crystal clear by the discovery by Joseph springs to mind) or whenever we are https://doi.org/10.1038/s41550-017-0343-6

Nature Astronomy | VOL 1 | DECEMBER 2017 | 807 | www.nature.com/natureastronomy 807 © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.