A pulsar that seemed to break the rules was hiding a rare third star

When China’s FAST telescope found the millisecond pulsar PSR J0435+3233 apparently slowing about a hundred times faster than any other in the Galaxy, it looked like a challenge to pulsar physics. Two independent teams have now traced the anomaly to a hidden third star — roughly the mass of our Sun, on a stretched 73-year orbit — whose gravity fakes the slowdown. Correct for it, and the pulsar behaves perfectly normally; what remains is only the second known stellar triple to host a pulsar.

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