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PSR B1937+21

The record PSR J1748−2446ad broke. Science, arXiv and NRAO all print 642 Hz for B1937+21.

Also known as B1937+21
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Rotation rate

642Hz

Spin frequency of PSR B1937+21 as printed in the accounts of the pulsar that broke its record. Discovered in 1982. Not the current fastest.

VerifiedNational Radio Astronomy Observatory (opens source in a new tab)

Mechanism

Why it's so fast

PSR B1937+21 is a neutron star, a collapsed core spinning fast enough that its radio beam sweeps past like a lighthouse. The fastest of these were spun up further by a companion star.

  1. Collapse

    Shrinking a stellar core to city size, while keeping its angular momentum, drives the spin up. The telescope counts pulses. It does not watch the surface move.

  2. The measured frequency

    PSR B1937+21's page ranks the spin frequency the papers print. This note does not convert that into a surface speed the papers did not publish as the rank.

Nearby on this list: PSR J1748−2446ad.

Provenance

Every measurement

Claimed, measured and official figures side by side, each with its source. The ranked figure is marked.

  1. 642HzRanked figure

    Spin frequency of PSR B1937+21 as printed in the accounts of the pulsar that broke its record. Discovered in 1982. Not the current fastest.

    Verified
    National Radio Astronomy Observatory (opens source in a new tab)

Reference

Specs

Object
PSR B1937+21
Frequency
642 Hz
Found
1982
Status
Previous spin record

Context

Background

The same three accounts that print 716 Hz for PSR J1748−2446ad name the mark it replaced. Science says the 642-hertz pulsar B1937+21. The arXiv preprint says the 642-Hz pulsar B1937+21. NRAO says the previous record of 642 Hz, from a pulsar discovered in 1982. The ranked figure is 642 Hz.

The row is the previous record, kept so the list has the frequency the 2006 paper beat. It is not a new observation from 2026. No day in 1982 was printed in these three accounts, so the measurement has no date.

Spot a wrong number?

Every report is read by a person, and corrections are dated on the page.