That's the approximate radius of a neutron star, a.k.a. a pulsar.
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A circle with a radius of 1.8 km has a circumference of 11.31 km
radius = 48/2 = 24 km
Radius = approx 6050 km, so diameter = 12100 km.
A sphere with a radius of 687 km has a volume of 1,358,184,658.3 km3
C = 31.4 km