SWIFT J1756.9-2508 is a millisecond pulsar with a rotation frequency of 182 Hz (period of 5.5 ms). It was discovered in 2007 by the Swift Gamma-Ray Burst Explorer and found to have a companion with a mass between 0.0067 and 0.030 solar masses. It is thought that the companion is the remnant of a former companion star, now stripped down to a planetary-mass core. The pulsar is accreting mass from this companion, resulting in occasional violent outbursts from the accumulated material on the neutron star.
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SWIFT J1756.9-2508 Wikipedia(Text) CC BY-SA