Coronal mass ejection
A coronal mass ejection (CME) is a significant ejection of magnetic field and accompanying plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understanding of these relationships has not been established.
If a CME enters interplanetary space, it is referred to as an interplanetary coronal mass ejection (ICME). ICMEs are capable of reaching and colliding with Earth's magnetosphere, where they can cause geomagnetic storms, aurorae, and in rare cases damage to electrical power grids. The largest recorded geomagnetic perturbation, resulting presumably from a CME, was the solar storm of 1859. Also known as the Carrington Event, it disabled parts of the newly created United States telegraph network, starting fires and shocking some telegraph operators.
Near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME every five days.
Stellar coronal mass ejections[edit]
There have been a small number of CMEs observed on other stars, all of which as of 2016 have been found on red dwarfs.[54] These have been detected mainly by spectroscopy, most often by studying Balmer lines: the material ejected toward the observer causes asymmetry in the blue wing of the line profiles due to Doppler shift.[55] This enhancement can be seen in absorption when it occurs on the stellar disc (the material is cooler than its surroundings), and in emission when it is outside the disc. The observed projected velocities of CMEs range from ≈84 to 5,800 km/s (52 to 3,600 mi/s).[56][57] There are few stellar CME candidates in shorter wavelengths in UV or X-ray data.[58][59][60][61] Compared to activity on the Sun, CME activity on other stars seems to be far less common.[55][62] The low number of stellar CME detections can be caused by lower intrinsic CME rates compared to the models (e.g. due to magnetic suppression), projection effects, or overestimated Balmer signatures because of the unknown plasma parameters of the stellar CMEs.[63]