4.7 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Bow shock | 2/2 | https://en.wikipedia.org/wiki/Bow_shock | reference | science, encyclopedia | 2026-05-05T13:31:53.442567+00:00 | kb-cron |
If a massive star is a runaway star, or if the interstellar medium moves relative to the star, it can form an infrared bow-shock that is detectable in 24 μm and sometimes in 8μm of the Spitzer Space Telescope or the W3/W4-channels of WISE. In 2016 Kobulnicky et al. created the largest spitzer/WISE bow-shock catalog to date with 709 bow-shock candidates. To get a larger bow-shock catalog The Milky Way Project (a Citizen Science project) did map infrared bow-shocks in the galactic plane. The search identified 311 new bow shock candidates. This larger catalog will help to understand the stellar wind of massive stars. The closest stars with infrared bow-shocks are (within 130 parsec):
Most of them belong to the Scorpius–Centaurus association.
== Magnetic draping effect == A similar effect, known as the magnetic draping effect, occurs when a super-Alfvénic plasma flow impacts an unmagnetized object such as what happens when the solar wind reaches the ionosphere of Venus: the flow deflects around the object draping the magnetic field along the wake flow. The condition for the flow to be super-Alfvénic means that the relative velocity between the flow and object,
v
{\displaystyle v}
, is larger than the local Alfvén velocity
V
A
{\displaystyle V_{A}}
which means a large Alfvénic Mach number:
M
A
≫
1
{\displaystyle M_{A}\gg 1}
. For unmagnetized and electrically conductive objects, the ambient field creates electric currents inside the object, and into the surrounding plasma, such that the flow is deflected and slowed as the time scale of magnetic dissipation is much longer than the time scale of magnetic field advection. The induced currents in turn generate magnetic fields that deflect the flow creating a bow shock. For example, the ionospheres of Mars and Venus provide the conductive environments for the interaction with the solar wind. Without an ionosphere, the flowing magnetized plasma is absorbed by the non-conductive body. The latter occurs, for example, when the solar wind interacts with the Moon which has no ionosphere. In magnetic draping, the field lines are wrapped and draped around the leading side of the object creating a narrow sheath which is similar to the bow shocks in the planetary magnetospheres. The concentrated magnetic field increases until the ram pressure becomes comparable to the magnetic pressure in the sheath:
ρ
0
v
2
=
B
0
2
2
μ
0
,
{\displaystyle \rho _{0}v^{2}={\frac {B_{0}^{2}}{2\mu _{0}}},}
where
ρ
0
{\displaystyle \rho _{0}}
is the density of the plasma,
B
0
{\displaystyle B_{0}}
is the draped magnetic field near the object, and
v
{\displaystyle v}
is the relative speed between the plasma and the object. Magnetic draping has been detected around planets, moons, solar coronal mass ejections, and galaxies.
== See also == Shock wave Shock waves in astrophysics Heliosheath Fermi glow Bow shock (aerodynamics) IRC -10414
== Notes ==
== References == Kivelson, M. G.; Russell, C. T. (1995). Introduction to Space Physics. New York: Cambridge University Press. p. 129. ISBN 978-0-521-45104-8. Cravens, T. E. (1997). Physics of Solar System Plasmas. New York: Cambridge University Press. p. 142. ISBN 978-0-521-35280-2.
== External links == NASA Astronomy Picture of the Day: Bow shock image (BZ Cam) (28 November 2000) NASA Astronomy Picture of the Day: Bow shock image (IRS8) (17 October 2000) NASA Astronomy Picture of the Day: Zeta Oph: Runaway Star (8 April 2017) Bow shock image (HD77581) Bow shock image (LL Ori) More on the Voyagers Hear the Jovian bow shock (from the University of Iowa) Cluster spacecraft makes a shocking discovery (Planetary Bow Shock)