# Neutron Spin (DD-058)

> 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.

- Department: Space (also Science)
- First published: 2025-06-15
- Last updated: 2025-06-15
- Permalink: https://detailenjoyer.com/case/neutron-spin/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## On the timeline

- **1933**: Walter Baade and Fritz Zwicky propose that supernovae leave behind neutron stars
- **1967**: Jocelyn Bell and Antony Hewish detect the first pulsar
- **1982**: A pulsar spinning 642 times a second sets the speed record
- **2006**: PSR J1748-2446ad, spinning 716 times a second, is reported as the fastest known pulsar

Full timeline: https://detailenjoyer.com/timeline/?case=neutron-spin

## Quick facts

- **DD-058-F01**: Most pulsars spin a few times a second or slower; only millisecond pulsars, spun up by companion stars, reach hundreds of spins a second. _(Write-up · Exhibit D (Most are slower))_
- **DD-058-F02**: The fastest known pulsar, PSR J1748-2446ad, spins 716 times a second. _(Write-up · Exhibit E (Spun up by a partner))_

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

## Related case files

- [Stellar Birth (DD-037)](https://detailenjoyer.com/case/stellar-birth/): The other end of a star's life: a cold cloud collapsing into a new star.
- [Solar Prominence (DD-038)](https://detailenjoyer.com/case/solar-prominence/): Stellar magnetism closer to home: the plasma loops and eruptions of the Sun.
- [Alcubierre Drive (DD-060)](https://detailenjoyer.com/case/alcubierre-drive/): More extreme physics: pulsars are precise enough to test gravity, and the warp drive bends spacetime on paper.
- [Axisymmetry (DD-054)](https://detailenjoyer.com/case/axisymmetry/): Another case about spinning collapsed objects: neutron stars, the collapsed cores of massive stars.

## Reel vs. record

- **Confirmed**: neutron stars form when massive stars collapse, and conservation of angular momentum spins them up, as Baade and Zwicky first proposed in 1933. [NASA; Kaspi & Kramer]
- **Overstated**: most pulsars don't spin hundreds of times a second. Typical periods are a few tenths of a second to seconds, and the slowest takes almost 6.7 hours. [NASA; Kaspi & Kramer]
- **Missing the key step**: the pulsars that do spin hundreds of times a second weren't born that fast. They were 'recycled' by a companion star feeding them matter and angular momentum. [Hessels et al. 2006; NASA SVS]
- **Context**: the record is 716 spins a second (PSR J1748-2446ad, Terzan 5, reported in 2006). [Hessels et al. 2006; NRAO]
- **Footage note**: the opening explosion is credited to NASA video; the glowing star with twin beams is an artist's animation, not a telescope image. [frames]

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

- Duration: 14.0 s · Published: 2025-06-15
- File: https://detailenjoyer.com/assets/videos/DK7x1SlyqHn.mp4

### Transcript

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!

## Questions & answers

**Q: Who first proposed neutron stars, in 1933?**  
A: 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))_

**Q: What makes a collapsing core spin faster?**  
A: 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))_

**Q: Who detected the first pulsar in 1967?**  
A: 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))_

**Q: How fast do most pulsars spin?**  
A: 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))_

**Q: How fast does the record-holding pulsar spin?**  
A: 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))_

## Sources

- [Pulsars (NASA Science, Hubble)](https://science.nasa.gov/mission/hubble/science/science-behind-the-discoveries/hubble-pulsars/)
- [Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016)](https://arxiv.org/abs/1602.07738)
- [Hessels et al., A Radio Pulsar Spinning at 716 Hz (Science, 2006)](https://doi.org/10.1126/science.1123430)
- [Astronomers Discover Fastest-Spinning Pulsar (NRAO, 2006)](https://www.nrao.edu/pr/2006/mspulsar/)
- [Millisecond Pulsar with Gravitational Waves (NASA Scientific Visualization Studio)](https://svs.gsfc.nasa.gov/10143/)

## 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/