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I've recently watched a documentary about pulsars. I know they are spinning neutron stars but what blows my mind how fast some spin. What is the surface speed of the fastest ones and how close is it to light speed. Regards. Alan

Hello Alan,

My searching results are that the fastest confirmed measurement has stood since 2005 as 716 revolutions per second. That record is held by Pulsar PSR J1748-2446ad. Using that measurement and measurement of its radius Wikipedia calculates that therefore "At its equator it is spinning at approximately 24% of the speed of light, or over 70,000 km per second."

A challenger, XTE J1739-285, was reported in 2007 to be revolving at 1122 revolutions/sec. However that result can not be repeated and is in serious doubt. If true, the reported radius of 10.9 km would indicate slightly greater speed at the equator than J1748-2446ad.

Calculation of the equatorial speed if the 1122 rev/s data were to be confirmed:
Circumference = 2*pi*r = 68.5 km
speed = 1122rev/s*68.5 km/rev = 76,800 km/s

I hope this helps,


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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