The Jet and The Plane

“OK, Sy, I get your point about a black hole being more than a mystical event horizon hiding whatever’s inside it. I’ll give you it’s a structure with a trapped-light shell and a pumpkin-donut belt around that –“

“… if it’s rotating, Vinnie…”

“– if it’s rotating, but what does all that have to do with those huge jets coming out of the poles instead of the equator where they belong?”

Suddenly Newt Barnes, astrophysicist in training, is standing by our table. “You guys are talking my research topic, just the hottest thing in astrophysics these days. Those jets were the subject of over a thousand papers last year. Mind if I sit in?”

“Of course not.” “We’re all ears.”

“Well, there’s a couple more layers to peel before we can make a maybe connection. Vinnie, what’s the weirdest thing about those jets?”

“Like I said, they’re huge — millions of lightyears long.”

“True, but other structures are huge, too — galaxy superclusters, for instance. The real weirdness is how narrow the jets are — less than a degree wide, and they’ve maintained that tight geometry while they’ve grown for millions of years. We still don’t know what’s in a jet. If it’s a beam of charged particles you’d think they’d repel each other and spread out almost immediately. If the particles are uncharged they’d bang into each other and into the prevailing interstellar medium. Random collisions would spread the beam out maybe a little slower than a charged-particle beam but still. A photon beam would be more stable but you’d need a really good collimating mechanism at the jet’s base to get the waves all marching so precisely.”

“What’s left, dark matter?”

“Almost certainly not. Many jets emit huge quantities of electromagnetic radiation at all frequencies from radio up through X-rays and beyond. Dark matter doesn’t do electromagnetism. No, jets are somehow created from normal stuff. The question is, how is it kept under such tight control?”

“The other question is, where’s all that stuff coming from if nothing can escape outta the event horizon?”

“Ah, that has to do with yet another part of the structure — the accretion disk.”

“What they got that orange picture of, right? Big ring like Saturn’s.”

“Well, similar shape, but different origin, different composition and very different dynamics. Saturn’s rings are mostly water-ice, built up from the debris of ice-moons that collided or were pulled apart by tidal forces. A black hole’s accretion disk is made up of planets, dust particles, atoms, whatever junk was unfortunate enough to be too close when the black hole passed by. Pick any incoming object and call it Freddie. Unless Freddie and the event horizon’s core are on an exact collision course, Freddie gets swept up by the disk.”

“Then what happens?”

“Freddie collides with something already in the disk. Lots of somethings. Each collision does two things. One, Freddie and the something break into smaller pieces. Two, some of Freddie’s gravitational potential energy relative to the core is converted to heat, making the collision debris package hotter than Freddie and the something were to begin with. After a while, Freddie gets ground down to atoms or smaller and they’re all really hot, radiating intensely just like Planck and Einstein said they would.”

“So we got a ring like Saturn’s, like I said.”

“Only sort of. Saturn has half-a-dozen distinct rings. They shine by reflected sunlight, the middle ring is brightest and broadest, and the innermost ring is dark and skinny. Our only direct accretion disk image so far is a one blurry view, but the object shines with its own light and in theory the disk isn’t segmented. There should be just one ring and it’d be brightest at a sharp inner edge.”

“Why’s that?”

“The light’s produced by hot particles. Heat generation’s most intense where the gravity well is steepest. That’s nearest the core. For a non-spinning black hole the threshold is one-sixth of the horizon’s diameter. If Freddie gets knocked the slightest bit closer than that it’s doomed to fall the rest of the way in. The edge is closer-in if the hole’s rotating but then Freddie has an interesting time. Relatively.”

“Gonna be frames again, right?”

“Yeah.”

~~ Rich Olcott

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