Magnetars

At a glance

Key points

Starquakes on their crusts release giant flares; one in 2004 briefly outshone the full Moon in gamma rays.

• Fields 1,000× a normal neutron star's
• A 2004 flare outshone the full Moon in gamma rays
• A Milky Way magnetar made a fast radio burst

The magnetar idea

In 1992 Robert Duncan and Christopher Thompson suggested that some neutron stars are born with magnetic fields around 10¹⁵ gauss, amplified by a dynamo in the turbulent first seconds after collapse, while the newborn star spins fast. The slow decay of that field, rather than rotation, would then power the star's X-rays and outbursts. The idea tied together two puzzling families of objects, the soft gamma repeaters and the anomalous X-ray pulsars.

Starquakes

The intense field stresses the solid crust until it cracks, snapping and reconnecting field lines and releasing a burst of gamma rays.

Slow spinners, few in number

Magnetars rotate slowly, typically once every few seconds, because their enormous fields act as a brake. Only a few dozen are known, in the Milky Way and the Magellanic Clouds, many of them found only when they flared. In 2022 NASA's IXPE measured polarised X-rays from 4U 0142+61, about 13,000 light-years away, and found a pattern best explained by a bare solid crust, though alternative models are still being tested.

Giant flares

Only a handful of giant flares have been recorded: from the Large Magellanic Cloud in 1979, from SGR 1900+14 in 1998, the record-breaking 2004 flare of SGR 1806-20, and in 2023 one from the galaxy M82. From far away, the brief opening spike of such a flare looks like a short gamma-ray burst, so some short bursts catalogued in other galaxies may really be magnetar flares.

What we still don't know

Why only some neutron stars become magnetars, how long their fields stay so strong, and whether all fast radio bursts, or only some, come from them.

Related entries

• Neutron starsCity-sized stellar cores
• Fast radio burstsMillisecond flashes from across the universe

Sources

1. Olausen & Kaspi 2014: the McGill Magnetar Catalog (arXiv) (opens in a new tab)
2. NASA Science: Hubble Messier catalog: M82 (opens in a new tab)
3. NASA Imagine the Universe: neutron stars (opens in a new tab)
4. NASA: IXPE finds powerful magnetic fields (opens in a new tab)
5. Palmer et al. 2005, Nature (arXiv) (opens in a new tab)
6. Bochenek et al. 2020, Nature (opens in a new tab)
7. Mereghetti 2008, A&A Review (arXiv) (opens in a new tab)
8. Duncan & Thompson 1992, ApJ 392:L9 (opens in a new tab)
9. Mereghetti et al. 2024, Nature (arXiv) (opens in a new tab)

Last reviewed 10 Oct 2026 against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.