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head–tail galaxy

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An elliptical galaxy in which strong radio emission in the nucleus (the head) is accompanied by an irregular tail of diffuse radio emission that may extend for hundreds of thousands of light years. The head and/or tail may be double. The radio emission is synchrotron radiation from energetic electrons, as in double-lobed radio galaxies, but the motion of the galaxy through a tenuous intergalactic medium has apparently caused the plasma jets to be swept back in the wake of the galaxy.

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