magnetar

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A magnetar is a type of neutron star with a surface magnetic field of 10⁹–10¹¹ tesla (for comparison, the record artificial field is only 10³ T). Inside is a superfluid neutron flux, superconducting protons, and a solid crust. Activity is powered by stored magnetic energy: crust fractures (starquakes) release up to 10⁴⁰ J within fractions of a second as gamma-ray flares. Magnetic braking explains periodic pulsations and X-ray emission.

History

In 1992, Robert Duncan and Christopher Thompson proposed the existence of magnetars to explain the sources of soft gamma repeaters (SGR). The first such object, SGR 0526-66, was observed back in 1979.

How it works

A magnetar is born during the core collapse of a massive star. Rapid rotation and convection act as a dynamo, amplifying the magnetic field to 10¹¹ T (the Earth's field is about 5×10⁻⁵ T). Over time, the field decays, releasing energy that heats the crust and causes gamma-ray flares.

💡 If a magnetar were at the Moon's distance, its field would erase data from magnetic media. Twice as close, it would attract iron objects with a force far exceeding human muscles.

A magnetar is a neutron star whose field exceeds the quantum electrodynamics limit Bₖ ≈ 4.4×10⁹ T, where vacuum polarization becomes nonlinear. The internal field can reach 10¹² T; it is generated by a dynamo mechanism due to differential rotation and convection in the first seconds after collapse. The surface emits X-rays as a blackbody with a temperature of 0.1–1 keV, and flares have a synchrotron nature. Magnetohydrodynamic processes in the crust cause deformations and fractures (starquakes) with the release of hard gamma radiation.

History

On March 5, 1979, satellites detected a burst from object SGR 0526-66 – subsequently the first identified magnetar. The concept of a magnetar was introduced by Robert Duncan and Christopher Thompson in 1992 to explain repeating gamma-ray bursts with a soft spectrum. In 1998, the detection of pulsations from the anomalous X-ray pulsar 1E 2259+586 confirmed the model: a field of about 6×10⁹ T. Today, more than 30 magnetars are known, including SGR 1806-20, whose 2004 flare was the brightest extrasolar gamma-ray event.

How it works

The strong magnetic field is generated by an alpha-omega dynamo: differential rotation (omega effect) and convective twist (alpha effect) in a rapidly rotating (milliseconds) protoneutron star. Upon cooling, the field is frozen into the superconducting proton fluid. Ohmic dissipation and ambipolar diffusion lead to field decay, heating, and crust deformations. Magnetohydrodynamic instabilities and magnetic reconnection cause gamma-ray flares. The magnetosphere is filled with plasma; rotation induces an electric field, accelerating particles to relativistic energies and producing non-thermal emission. Maxwell's equations describe the field structure.

B_{\text{cr}} = \frac{m_e^2 c^3}{e \hbar}

Bcr is the critical magnetic induction at which the cyclotron energy equals the electron rest energy; me is the electron mass, me ≈ 9.10938356×10⁻³¹ kg; c is the speed of light, c ≈ 2.99792458×10⁸ m/s; e is the elementary charge, e ≈ 1.602176634×10⁻¹⁹ C; ℏ is the reduced Planck constant, ℏ ≈ 1.054571817×10⁻³⁴ J·s. For magnetars, B > Bcr, leading to pair production from vacuum.

u = \frac{B^2}{2\mu_0}

u is the volumetric energy density of the magnetic field; B is the magnetic induction; μ0 is the magnetic constant, μ0 = 4π×10⁻⁷ H/m (exact in SI). At B = 10¹¹ T, u ~ 4×10²⁷ J/m³, comparable to the energy density of nuclear matter.

Open problems & fun facts

Mechanism for generating such a strong magnetic field: does it require an extreme period of the newborn star (milliseconds) or special collapse conditions?; Connection between magnetars and fast radio bursts: are they the only source or just one option?; Existence of an internal super-strong field and its influence on the equation of state of nuclear matter.; Field evolution: why do some magnetars remain active for thousands of years, while others quickly fade?

💡 In a magnetar's field, a single photon can transform into an electron-positron pair due to a quantum electrodynamics effect that cannot be reproduced in the laboratory.

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arXiv:2605.14050v1 · 2026-05-13

magnetar

History

How it works

History

How it works

History

How it works

Open problems & fun facts

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