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XTE J1751−305
42.42 min
Accreting millisecond pulsar. Orbital period 2545.3414(38) s, reported as 42 minutes.
A tiny spinning star and a lighter companion race around each other. RXTE timed the dance at 2545.3 seconds. The discoverers wrote that as 42 minutes. The seconds are 42.42 minutes, not 42.00. A clock in the sky, not a hole through the Earth.
What it supports
A measured compact-binary period. Markwardt et al., ApJ 575, L21 (2002). P_b = 2545.3414(38) s. Spin 435.3 Hz. Later timing keeps 2545.342(2) s. UltraCompCAT prints 42.42235 ± 0.00006 min. In 2002 it was the shortest known millisecond-pulsar orbit. That record moved. The period did not.
What it does not
Not 42 minutes exact. Not the gravity-tunnel textbook. Not Mariner 2’s 42-minute Venus scan. The 435 Hz spin is a different number.
Calculation
2545.3414 s ÷ 60 = 42.422357 min.
Orbital Doppler of the 435 Hz pulsations. RXTE PCA.
ExactnessApproximate
Form42 as duration
Unitminutes
Strengthhard
When2002
Hung9 September 2026