An intense flash from the Milky Way's black hole illuminated gas far outside of our galaxy approximately 3.5 million years ago. This flash is believed to have illuminated a huge, ribbon-like tail of gas orbiting the Milky Way. Called the Magellanic Stream, this long trail lies far outside of our galaxy, at an average distance of 200,000 light-years. Like an aircraft contrail, it extends from neighboring dwarf galaxies, the Large and Small Magellanic Clouds. Researchers made ultraviolet measurements of distant quasars behind the Magellanic Stream. As the ultraviolet light from the quasars passed through the stream, Hubble recorded the evidence of how the flash altered the gas.
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Album / NASA, ESA, and L. Hustak (STScI) / Science Source