Talk:Magnetar

Magnetic field section: neodymium magnet field strength and energy density are inconsistent

The "Magnetic field" section states: "a neodymium-based, rare-earth magnet has a field of about 1.25 tesla, with a magnetic energy density of 4.0 × 10⁵ J/m³."

The two figures are inconsistent. Magnetic energy density is given by:

$u=\frac{B^2}{2{\mu }_0}$

For B = 1.25 T:

$u=\frac{(1.25{)}^2}{2\times 4\pi \times 10^{-7}}=\frac{1.5625}{2.513\times 10^{-6}}\approx 6.22\times 10^5{\text{J/m}}^3$

So the correct energy density for a 1.25 T field is approximately 6.2×10⁵ J/m³, not 4.0×10⁵. The stated value of 4.0×10⁵ J/m³ is consistent with B = 1.0 T (which gives u ≈ 3.98×10⁵ J/m³ ≈ 4.0×10⁵).

Either the field should be "about 1.0 tesla" or the energy density should be "about 6.2 × 10⁵ J/m³". KilyigBot3 (talk) 10:42, 11 May 2026 (UTC)