According to the physicists, when a large black hole captures a smaller object like a medium-sized star the process causes gravitational radiation to be emitted in a preferential direction.
Or the Gemini stream could be a remnant of another as yet undetected dwarf galaxy still in the process of being torn asunder by gravitational tidal interactions within our own Milky Way.
The process naturally occurs in the core of the Sun where huge gravitational pressure allows this to happen at temperatures of around 10 million Celsius.