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Neutron Spin

Short answer: Neutron stars are the collapsed cores left after massive stars explode as supernovae, an idea Walter Baade and Fritz Zwicky proposed in 1933. As the core shrinks to about the size of a city, conservation of angular momentum makes it spin much faster, like a skater pulling in her arms.

Pulsars are neutron stars whose beams of radiation, from near their magnetic poles, sweep past Earth like a lighthouse. Jocelyn Bell and Antony Hewish detected the first one in 1967. Most pulsars turn only a few times a second at most. The ones that spin hundreds of times a second are millisecond pulsars, old neutron stars 'recycled' by matter and angular momentum from a companion star. The record holder, PSR J1748-2446ad, spins 716 times a second.

VideoWrite-up5 sources

In collections:The Sun and the Stars

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What should you know about Neutron Spin?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Most pulsars spin a few times a second or slower; only millisecond pulsars, spun up by companion stars, reach hundreds of spins a second.

    DD-058-F01 · Write-up · Exhibit D (Most are slower)

  2. The fastest known pulsar, PSR J1748-2446ad, spins 716 times a second.

    DD-058-F02 · Write-up · Exhibit E (Spun up by a partner)

Video transcript: Neutron Spin: Dead Stars That Spin Hundreds of Times a Second

DID YOU KNOW? Formed from the collapse of massive stars, neutron stars spin at astonishing speeds, due to the conservation of angular momentum. Some neutron stars called pulsars spin hundreds of times per second, emitting precise beams of radiation. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 14.0s Reel ·

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The write-up

Dead stars that spin hundreds of times a second. Most pulsars turn about once a second. The fastest are spun up by a companion star.

  1. Exhibit A

    Born in a collapse

    In 1933, Walter Baade and Fritz Zwicky proposed that a massive star collapsing in a supernova could leave behind a tiny, extremely dense neutron star.

  2. Exhibit B

    Why they spin fast

    When a stellar core collapses, it keeps its angular momentum. Shrinking to a fraction of its size makes it rotate far faster, the way a spinning skater speeds up by pulling in her arms.

  3. Exhibit C

    Cosmic lighthouses

    Pulsars emit beams of radiation from near their magnetic poles. As the star turns, the beams sweep past Earth as regular pulses. Jocelyn Bell and Antony Hewish found the first in 1967, and more than 3,000 are now known.

  4. Exhibit D

    Most are slower

    Most pulsars spin only a few times a second or slower; the slowest takes almost 6.7 hours to turn once. Those spinning hundreds of times a second are millisecond pulsars, with periods of 1 to 10 milliseconds.

  5. Exhibit E

    Spun up by a partner

    Millisecond pulsars are 'recycled': matter and angular momentum from a companion star spin up an old neutron star. The fastest known, PSR J1748-2446ad in the globular cluster Terzan 5, spins 716 times a second, beating a 642-Hz record from 1982.

  6. Exhibit F

    Precise clocks

    Their steady pulses make pulsars some of nature's most precise clocks, which astronomers use to test gravity.

Questions people ask about Neutron Spin

Who first proposed neutron stars, in 1933?

They tied them to supernovae.

Source: Write-up · Exhibit A (Born in a collapse) · Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016); Pulsars (NASA Science, Hubble)

What makes a collapsing core spin faster?

It's like a skater pulling in her arms.

Source: Write-up · Exhibit B (Why they spin fast) · Pulsars (NASA Science, Hubble); Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016)

Who detected the first pulsar in 1967?

More than 3,000 are now known.

Source: Write-up · Exhibit C (Cosmic lighthouses) · Pulsars (NASA Science, Hubble); Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016)

How fast do most pulsars spin?

Only millisecond pulsars spin hundreds of times a second.

Source: Write-up · Exhibit D (Most are slower) · Pulsars (NASA Science, Hubble); Millisecond Pulsar with Gravitational Waves (NASA Scientific Visualization Studio); Hessels et al., A Radio Pulsar Spinning at 716 Hz (Science, 2006)

How fast does the record-holding pulsar spin?

It's PSR J1748-2446ad in Terzan 5.

Source: Write-up · Exhibit E (Spun up by a partner) · Hessels et al., A Radio Pulsar Spinning at 716 Hz (Science, 2006); Astronomers Discover Fastest-Spinning Pulsar (NRAO, 2006)

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. Who first proposed neutron stars, in 1933?

    1. Einstein and Bohr
    2. Baade and Zwicky
    3. Bell and Hewish
    4. Hubble and Sagan
    Show the answer

    Answer: B. Baade and Zwicky They tied them to supernovae. Source: Write-up · Exhibit A (Born in a collapse) · Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016); Pulsars (NASA Science, Hubble)

  2. What makes a collapsing core spin faster?

    1. Magnetism alone
    2. Conservation of angular momentum
    3. Dark matter
    4. Solar wind
    Show the answer

    Answer: B. Conservation of angular momentum It's like a skater pulling in her arms. Source: Write-up · Exhibit B (Why they spin fast) · Pulsars (NASA Science, Hubble); Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016)

  3. Who detected the first pulsar in 1967?

    1. Jocelyn Bell and Antony Hewish
    2. Carl Sagan
    3. Vera Rubin
    4. Edwin Hubble
    Show the answer

    Answer: A. Jocelyn Bell and Antony Hewish More than 3,000 are now known. Source: Write-up · Exhibit C (Cosmic lighthouses) · Pulsars (NASA Science, Hubble); Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016)

  4. How fast do most pulsars spin?

    1. Hundreds of times a second
    2. A few times a second or slower
    3. Once a year
    4. They don't spin
    Show the answer

    Answer: B. A few times a second or slower Only millisecond pulsars spin hundreds of times a second. Source: Write-up · Exhibit D (Most are slower) · Pulsars (NASA Science, Hubble); Millisecond Pulsar with Gravitational Waves (NASA Scientific Visualization Studio); Hessels et al., A Radio Pulsar Spinning at 716 Hz (Science, 2006)

  5. How fast does the record-holding pulsar spin?

    1. 30 times a second
    2. 716 times a second
    3. 10,000 times a second
    4. Once a minute
    Show the answer

    Answer: B. 716 times a second It's PSR J1748-2446ad in Terzan 5. Source: Write-up · Exhibit E (Spun up by a partner) · Hessels et al., A Radio Pulsar Spinning at 716 Hz (Science, 2006); Astronomers Discover Fastest-Spinning Pulsar (NRAO, 2006)

Cite this case file

Easterling, Marcus. "Neutron Spin." The Detail Department (DetailEnjoyer), case file DD-058, last updated Jun 15, 2025. https://detailenjoyer.com/case/neutron-spin/

Permalink: https://detailenjoyer.com/case/neutron-spin/ · Last updated

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