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How to make a blazar: Slam two galaxies together and watch them feed a huge black hole

13 Aug 2020, 13:00 UTC
How to make a blazar: Slam two galaxies together and watch them feed a huge black hole
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Some galaxies aren’t quiet like ours. Instead, they blaze out vast amounts of energy from their cores. We call these active galaxies.

Every big galaxy has a supermassive black hole in its center. If that black hole is actively feeding, the material falls into a disk around it, heats up hugely, and emits a lot of light. Also, magnetic fields wind up in the center like a tornado, and can launch ridiculously powerful beams of energy away from the disk, up and down. Astronomers call these jets.

Jets can be immensely bright, and if one is aimed right at us they swamp the light from the rest of the galaxy. We see very high-energy gamma rays from these jets, as well as lots of radio waves and X-rays. We call these galaxies blazars.

But why are some galaxies like this? For a long time it’s been supposed that if two galaxies collide, the event can send huge waves of gas down into the centers of the galaxies where the supermassive black hole waits, which then triggers the activity. But with blazars it’s hard to tell because the jets are so bright.

But now, for the first time, it looks like ...

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