Stellar Remnants
Magnetar
Neutron stars with the strongest magnetic fields in the universe — 10¹⁴-10¹⁵ Gauss
A magnetar is a neutron star with an extreme magnetic field — typically 10¹⁴-10¹⁵ Gauss (10¹⁰-10¹¹ Tesla). For comparison: Earth's field 1 G, refrigerator magnet 100 G. Magnetar field is ~10¹³× Earth's. Energy stored in field decays through giant flares (releases 10⁴⁰-10⁴⁶ J), magnetar bursts, and possibly fast radio bursts (FRBs). About 30 known. Lifetime as magnetar: ~10⁴ years before field decays. Likely formed by fast-spinning collapsing core during supernova.
- Magnetic field10¹⁴-10¹⁵ G (vs 1 G Earth)
- Field energy10⁴⁰-10⁴⁷ J (massive)
- Period1-10 s (slower than typical pulsars)
- Lifetime as magnetar~10,000 years (field decays)
- Known magnetars~30 confirmed
- Discovered1979 (giant flare from SGR 0526-66)
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Why magnetars matter
- Extreme magnetic fields. Strongest in universe.
- Fast radio bursts. Key candidate progenitor.
- QED tests. Beyond critical field strength.
- Stellar evolution. Subset of NS population.
- Crustquake physics. Insights into neutron matter.
- High-energy astrophysics. Source of soft gamma repeaters.
- FRB cosmology. Future probe of intergalactic medium.
Common misconceptions
- All NS are magnetars. ~1% of total NS population.
- Magnetars decay quickly. Field decay over ~10⁴ yr; star longer.
- All FRBs from magnetars. Many likely; some sources unknown.
- Magnetar fields static. Decay; can flare; can be unstable.
- Magnetars are visible. Mostly quiescent in X-ray; bright only during flares.
- Magnetars common in binaries. Most are isolated; few in binary systems.
Frequently asked questions
How does a magnetar form?
Specific supernova progenitors. If newly-formed neutron star spins very fast (~ms) plus has high temperature, dynamo amplifies field to extreme values. Most NS have fields ~10¹² G; magnetars have field ~10¹⁵ G. Conditions: massive progenitor (10⁵-10⁶ M_sun explosion energy), specific rotation parameters.
What are giant flares?
Sudden release of magnetic energy from magnetar surface. Triggered by magnetic field instability or "starquake" (fracture of NS crust). Energy: 10⁴⁰-10⁴⁶ J in seconds. Soft Gamma Repeater (SGR) sources show this — three giant flares ever observed in our galaxy. Magnetar SGR 1806-20 in 2004 affected Earth's ionosphere.
What's the "magnetar model" of FRBs?
Fast Radio Bursts (FRBs) — millisecond radio pulses from extragalactic sources. Many seem to come from magnetars. CHIME telescope detected an FRB from a known magnetar in our own galaxy (April 2020). Confirms at least some FRBs originate from magnetars. Other sources possible too.
Are magnetars dangerous?
Only if very close. SGR 1806-20 giant flare (2004): equivalent of 10⁴² J released; observable across galaxy. Earth ionosphere disrupted briefly (despite being 50,000 ly away). Closer magnetar (within 10 ly): would damage atmosphere. None known that close.
How are magnetars different from pulsars?
Both are neutron stars. Pulsars: rotation drives emission; field ~10¹² G; often radio-loud; periods ms-s. Magnetars: magnetic decay drives emission; field ~10¹⁵ G; X-ray quiescent + flares; periods 1-10 s. Magnetars can have pulsar-like behavior; pulsars can show magnetar-like phases. Spectrum of behaviors.
How many magnetars exist?
~30 confirmed in our galaxy. Total in galaxy estimated ~10⁴-10⁵ (most invisible without flare). Lifetime as magnetar ~10⁴ yr; total NS lifetime ~10⁹ yr — so ~1% of NS are active magnetars at any time. Galaxy contains ~10⁹ NS total.
What's beyond the magnetar field strength?
Quantum critical field B_QED = m_e²c³/eℏ ≈ 4.4×10¹³ G. Below this, classical electromagnetism. Above: QED effects. Magnetar fields exceed B_QED — exotic physics: vacuum birefringence, photon splitting, resonant cyclotron scattering. Lab for testing QED in extreme regimes.