Cosmology

EstablishedDirect Ampère reading of the named disk. The particle halo is retired as inventory. This current is not that retirement.

Galactic Current Drift

The net current in the warm ionized disk moves its carriers nanometres per second. In 12,000 years that is a few kilometres.

Last updated: 7 October 2026

Reading this entry

The galactic-current page reads a disk field of a few microgauss through Ampère's law and finds the carrier drift in the warm ionized gas. At the frozen Peratt inputs the mean slip is 8.94×10⁻⁹ m s⁻¹, so a carrier travels metres in a human lifetime and a few kilometres in 12,000 years.

What this is used for

Local-stream and dark-matter notes cite this drift when they need the Milky Way disk current as a plasma quantity. The enclosed current I = BR/μ₀ = 1.044×10¹⁷ A and the drift table are the shared inputs, with magnetic energy, plasma beta, and the gyroradii in the same reading.

Walk through

Ampère's law supplies the disk-mean drift v_d = B/(μ₀ n_e e h) = 8.94×10⁻⁹ m s⁻¹, so one year is 0.282 m and 12,000 years is 3.39 km. Orbital speeds nearby are about 220 km s⁻¹, and the electron thermal speed at 8000 K is 3.48×10⁵ m s⁻¹, making the drift 2.57×10⁻¹⁴ of that thermal speed. The frozen inputs are B = 5 μG, n_e = 0.03 cm⁻³, T = 8000 K, R = 8.5 kpc, and h = 0.3 kpc, and the enclosed current is I = BR/μ₀ = 1.044×10¹⁷ A, with J = B/(μ₀ h) = n_e e (v_i − v_e). The magnetic energy density is 0.621 eV cm⁻³, the banked plasma beta is 0.033, and the proton and electron gyroradii are 170 km and 4.0 km.

The Milky Way disk carries a real magnetic field of a few microgauss. Ampère's law reads a net current from that field. Spread through the warm ionized gas, the carriers slip past one another at

Disk-mean drift at the frozen inputs below. One second of this drift is 8.94 nanometres.

How far a carrier travels

Clock	Distance
One second	8.94 nm
One year	0.282 m
Eighty years	22.6 m
12,000 years	3.39 km
One Hubble time at	4,000 km

The Hubble-time row is . Orbital speeds in the same disk are about . The electron thermal speed at is . The drift is of that thermal speed.

The inputs

The numbers are the frozen Peratt disk, catalogue values rather than a fit:, , , , . The enclosed current on a path of length is

That current, spread through a radial cut of height , is the mean density . Quasi-neutrality writes , so is the slip between the protons and the electrons. The mass of this gas is the warm ionized medium, about . The stars and the neutral hydrogen sit in the banked disk split beside it, near and .

A full reversal of the same field doubles the surface current and doubles the drift. A thinner Harris sheet raises it. At a half-thickness of the peak drift is , and 12,000 years of that peak is . At the peak is and the travel is . , , and are catalogue orders. A factor of a few in any one of them moves the drift by that factor, and the 12,000-year travel stays a few kilometres.

What stays free

Drift kinetic energy is of the magnetic energy if the electrons carry the slip, and if the protons do. Magnetic energy itself is , and the banked plasma is . The energy does not choose the sign. Faster canceling pairs can sit inside the circuit and still leave this Ampère remainder. The proton gyroradius is and the electron gyroradius is .

A 12,000-year crossing of a galactic sheet is a different motion from this drift. At the Sun travels in 12,000 years. The published local magnetic reversal is a tilted plane 0.25–0.55 kpc from the Sun. The local gas wave oscillates over tens of millions of years. The Sun–Pleiades circumference at 135 pc and 20 km/s is 41.5 Myr, on the local stellar stream page. The heliospheric current sheet turns over with the solar rotation and the 11-year cycle.

Integrity

The drift is the direct Ampère reading of the named disk. The halo stays the open leftover. This page charters no ledger row and does not promote.

Source Documents

The working note for this page. It charters no ledger row and does not promote.

Galactic current drift

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