At the core of most galaxies is a supermassive black hole (SBH) thousands or millions of times heavier than the Sun. They’re generally seen in radio or x-ray emission powered by the black hole’s accretion of surrounding material. Some actively accreting galactic nuclei are the brightest steady lights in the distant cosmos. Although the nearest SBH, 27 000 light-years away at the center of the Milky Way, is surprisingly quiescent, its proximity makes it attractive for the study of accretion flow in galactic nuclei.

Five months ago that study received a serendipitous gift. Several observing teams discovered a radio pulsar less than a light-year from the Milky Way’s SBH. Radio pulsars had long been sought in the galaxy’s innermost precincts. But until now, none had been found within 70 ly of the center.

Radio pulsars, rapidly spinning neutron stars with sweeping radio beams, are superb celestial clocks. This new one...

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