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Cosmic Rays, Dead Quasars, & Wild Speculation (Patreon)

Published:
2017-02-19 23:47:21
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Hey guys, I just wanted to share some fun stuff one of my research groups has been doing: figuring out whether dead quasars may be the source of the most energetic cosmic rays! This is a picture of the magnetic field around a spinning supermassive black hole. Some undergrad(!!) students calculated this (hey Roberto, Rafael & Juan!). They then used it to figure out the energy spectrum of the atomic nuclei that get blasted out into the universe by these fields. It turns out that these nuclei can match the observed highest-energy cosmic ray spectrum... so, from a wildly theoretical and not-yet-peer-reviewed standpoint, it's looking good! 

Here's the paper by the way. It just went up on the archive. Not yet accepted, so ssshhh!

https://arxiv.org/abs/1702.00053

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Comments

Anonymous

Awesome. Please keep these coming!

Anonymous

Cool!.. Very interesting!

Anonymous

Very interesting. I'm curious where you think the transition is between galactic and extragalactic cosmic rays? It sounds like you're saying that extragalactic secondaries can explain the spectrum below the ankle. How low does that go? All the way down to the knee? If so, can you explain 3 PeV particles escaping and propagating all the way to our galaxy? What is your prediction for the composition over that whole energy range? I work on UHECRs, so I'd be interested in your thoughts.

Anonymous

Preview access to a physics paper, well that's a "first time in my life" thing I can now check on my list. It's Probably too technical for my layman-but-still-better-than-most-layman physic skill and comprehension, but I'll read this with interest! I love working in IT, but something I kind of regret being so lazy when I was in high school and college. kudo. to your undergrads! Thank you!

pbsspacetime
>>3991103

Hey Paul, sorry for the slow response. I admit to being the quasar guy on this paper, not the cosmic ray guy. That would be Luis Anchordoqui (of the Auger collaboration). This is my first foray into CR stuff, but I expect not my last. But the crux of the paper is that the ankle in the UHECR spectrum at ~10^10 GeV can be explained by adding a new population of cosmic rays on top of the high-energy tail of extragalactic population that dominates just below the ankle. Obviously, we think this new source could be nuclei accelerated in the magnetic fields of supermassive black holes. The numbers work out at the high energy end - although only for heavy nuclei, not protons. It's unlikely that these dominate at energies below the ankle, in part because the extragalactic sources are too isotropic between the ankle and the knee. You'd expect some clustering for SMBH-sourced CRs, as is seen at the highest energies. However protons sourced from photodisintegration of heavier nuclei should be present between the ankle and the knee.