BBC Earth (Asia) - - Science -

A ‘shock wave’ is the dis­tur­bance of ma­te­rial that’s cre­ated when a wave moves through a medium at greater than the lo­cal speed of sound. Pro­vided there is a ‘medium’ of suf­fi­cient den­sity through which a shock wave can travel, there is no rea­son why shock waves can’t form in space. How­ever, be­cause most en­vi­ron­ments in space are of ex­tremely low den­sity, tra­di­tional shock waves in­volv­ing the col­li­sion of par­ti­cles, such as those that give rise to a ‘sonic boom’, are rare. But there are other kinds of shock waves that can oc­cur in low-den­sity en­vi­ron­ments. For ex­am­ple, the shock can be prop­a­gated by pho­tons in­ter­act­ing with elec­trons, by a distri­bu­tion of high en­ergy par­ti­cles or by mag­netic ef­fects. So, shock waves are ac­tu­ally quite com­mon in space. In­ter­plan­e­tary shock waves can oc­cur due to so­lar flares. ‘Bow shocks’ are formed by the in­ter­ac­tion of the so­lar wind with plan­e­tary mag­ne­to­spheres. Su­per­novae cre­ate pow­er­ful shocks, both within the star col­laps­ing to form the ex­plo­sion and also mov­ing through the in­ter­stel­lar medium it­self. In­ter­stel­lar shocks can also oc­cur sim­ply by the col­li­sion or col­lapse of gas clouds. Black holes, high-den­sity ob­jects such as pul­sars, as well as merg­ing gal­ax­ies (and even just the mo­tion of gal­ax­ies them­selves) are also known to form shock waves of var­i­ous forms. AGu

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