Active galaxies give off bright radiation from their cores, where gas heats up as it is compressed into a swirling accretion disk encircling the black hole.

活动星系从它们的核部发出明亮的光芒，在那里，气体被加热并压缩成一个漩涡状的圆盘，漩涡的中心便是黑洞。

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This scenario may explain why only 10% of active galaxies have radio jets, and how active galaxies evolve over time.

这种假设或许可以解释为什么活跃星系中只有10%存在喷流，以及它们如何持续演变。

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The scientists rounded up the usual suspects — 140 active galaxies in all — and compared them with a control group of 1200 inactive galaxies.

科学家们围捕了通常的嫌疑人——总共140个活跃星系——并将它们和一个1200个非活跃星系组成的对照组作比较。

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Blazars are a special case of "active galaxies" - those whose supermassive black holes spray out great quantities of light across the whole electromagnetic spectrum as they feed on surrounding matter.

BBC: Blazar Markarian 421's flare-up is cosmic coincidence

Active galaxies emit jets of light - up to trillions of times more energetic than the light we see - and a blazar is one with a jet pointing toward the Earth.

BBC: Blazar Markarian 421's flare-up is cosmic coincidence