Ergosphere of a rotating black hole. The inner event horizon is also not circular. See <a href="https://de.wikipedia.org/wiki/Ereignishorizont#Drehimpuls_und_elektrische_Ladung" class="extiw" title="de:Ereignishorizont">de:Ereignishorizont #Drehimpuls und elektrische Ladung</a>
<p><b>Original: </b> <a href="//commons.wikimedia.org/wiki/User:MesserWoland" title="User:MesserWoland">MesserWoland</a>
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<b>Vectorization: </b> <a href="//commons.wikimedia.org/wiki/User:Perhelion" title="User:Perhelion">Perhelion</a>
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Own work based on: <a href="//commons.wikimedia.org/w/index.php?title=File:Ergosphere.svg&amp;action=edit&amp;redlink=1" class="new" title="File:Ergosphere.svg (page does not exist)">File:Ergosphere.svg</a>