In astrophysics, a bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby flowing ambient plasma such as the solar wind. For Earth and other magnetized planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause. For stars, this boundary is typically the edge of the astrosphere, where the stellar wind meets the interstellar medium.
LL Orionis bow shock in Orion nebula. The star's wind collides with the nebula flow. Hubble, 1995
The bubble-like heliosphere moving through the interstellar medium and its different structures.
The bow shock around R Hydrae
Image: Heliosheath
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV. The composition of the solar wind plasma also includes a mixture of materials found in the solar plasma: trace amounts of heavy ions and atomic nuclei of elements such as C, N, O, Ne, Mg, Si, S, and Fe. There are also rarer traces of some other nuclei and isotopes such as P, Ti, Cr, and 58Ni, 60Ni, and 62Ni. Superimposed with the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. The boundary separating the corona from the solar wind is called the Alfvén surface.
Ulysses' observations of solar wind speed as a function of helio latitude during solar minimum. Slow wind (≈400 km/s) is confined to the equatorial regions, while fast wind (≈750 km/s) is seen over the poles. Red/blue colors show outward/inward polarities of the heliospheric magnetic field.
Laboratory simulation of the magnetosphere's influence on the solar wind; these auroral-like Birkeland currents were created in a terrella, a magnetised anode globe in an evacuated chamber.
This is thought to show the solar wind from the star L.L. Orionis generating a bow shock (the bright arc)
CME erupts from Earth's Sun