I got this from NewScientistSpace:
Intergalactic particle beam is longest yet found - space - 07 December 2007 - New Scientist Space
Here's the lead paragraph: "An intergalactic particle beam stretching for more than a million light years is the longest ever seen. According to the team that discovered this record breaker, it could help reveal how such jets of matter bind themselves together."
Image caption: "Colossal black holes at the centres of active galaxies power jets of matter that stretch far into space (Illustration: NASA)"