The Fermi Bubbles


How come nobody told me about the ‘Fermi bubbles’? If you could see gamma rays, you’d see enormous faint glowing bubbles extending above and below the plane of the Milky Way.

Even better, nobody is sure what produced them! I love a mystery like this.

The obvious suspect is the black hole at the center of our galaxy. Right now it’s too quiet to make these things. But maybe it shot out powerful jets earlier, as it swallowed some stars.

Another theory is that the Fermi bubbles were made by supernova explosions near the center of the Milky Way.

But active galactic nuclei—where the central black hole is eating a lot of stars—often have jets shooting out in both directions. So I’m hoping something like that made the Fermi bubbles. Computer models say jets lasting about 100,000 years about 2.6 million years ago could have done the job.

The Fermi bubbles were discovered in 2010 by the Fermi satellite: that’s how they got their name. I learned about them by reading this review article:

• Mark R. Morris, The Galactic black hole.

I recommend it! I get happy when I hear there are a lot of overlapping, complex, poorly understood processes going on in space. I get sad when pop media just say “Look! Our new telescope can see a lot of stars! I already knew there are a lot of stars. But the interesting stories tend to be written in a more technical way, like this:

Another cool thing: we may have detected some neutrinos emanating from the Fermi bubbles! These neutrinos have energies between 18 and 1,000 TeV. That’s energetic! Our best particle accelerator, the Large Hadron Collider, collides protons with an energy of about 14 TeV. This suggests that the Fermi bubbles contain a lot of very high-energy protons—so-called ‘cosmic rays’ — which occasionally collide and produce neutrinos.

• Paul Sutter, Something strange is happening in the Fermi bubbles,, September 4, 2019.

See also these:

• Rongmon Bordoloi, Andrew J. Fox, Felix J. Lockman, Bart P. Wakker, Edward B. Jenkins, Blair D. Savage, Svea Hernandez, Jason Tumlinson, Joss Bland-Hawthorn and Tae-Sun Kim, Mapping the nuclear outflow of the Milky Way: studying the kinematics and spatial extent of the Northern Fermi bubble, The Astrophysical Journal 834 (2017) 191.

• P. Predehl, R. A. Sunyaev, W. Becker, H. Brunner, R. Burenin, A. Bykov, A. Cherepashchuk, N. Chugai, E. Churazov, V. Doroshenko, N. Eismont, M. Freyberg, M. Gilfanov, F. Haberl, I. Khabibullin, R. Krivonos, C. Maitra, P. Medvedev, A. Merloni, K. Nandra, V. Nazarov, M. Pavlinsky, G. Ponti, J. S. Sanders, M. Sasaki, S. Sazonov, A. W. Strong, and J. Wilms, Detection of large-scale X-ray bubbles in the Milky Way halo.

Also try this, for something related but different:

• Jure Japelj, Astonishing radio view of the Milky Way’s Heart, Sky and Telescope, February 3, 2022.

6 Responses to The Fermi Bubbles

  1. Sir Light says:

    I love such kinds of science! “Something is happening somewhere and we have next to no idea what is causing it”. In our digital age it seems that Google knows everything, if you do not understand something it means that you did not study enough and some random dick in the chat will come and tell you how dumb you are. It is so fascinating from time to time to know that there actually are questions that no one knows the answer to

  2. Rob says:

    What generates TeV particles and how can I get one for my office?

    Also is anyone able to use these particles as a source for a cool experiment in particle physics?

    • John Baez says:

      We can create 7 TeV protons at the Large Hadron Collider. But creating neutrinos with energies much higher, between 18 and 1,000 TeV, is a lot harder! They’re coming out of the sky, but from where? We don’t know for sure! Here I was suggesting that some are created by collisions involving protons and such in the jets emitted by the supermassive black hole at the center of our galaxy. That’s a widely accepted theory. But there are also other candidate sources. I’m no expert on this, but this paper:

      • Matthew D. Kistler and John F. Beacom, Guaranteed and prospective Galactic TeV neutrino sources

      also mentions the Vela pulsar (which I’ll talk about soon) and its younger partner called Vela Jr..

      You could try to use these high-energy neutrinos for experiments but they’re quite rare, so what people actually do now is stuff like this: take a cubic kilometer of Antarctic ice near the South Pole, wait for high-energy neutrinos to hit it, and detect the resulting flashes of light using 5160 photomultipliers. This experiment is called IceCube.

  3. LNV says:

    It looks a bit like a 2p orbital, which is more energetic than a 2s one, which could be a “state” of the condensed galaxy? Advance apologies if the analogy seems asinine.

    • John Baez says:

      You’re not the first person to mention that to me. There might be a physical explanation of this process—like some sort of differential equation—that explains why it looks like a 2p orbital. People are still arguing about whether it’s caused by jets emanating from the black hole at the center of the Milky Way or multiple supernovas near the center. I favor the former theory.

  4. Wyrd Smythe says:

    I’m sorry! I meant to tell you, but I kept forgetting. They are pretty cool, although probably best appreciated from a bit of a distance. I’ve heard about jets from the centers of other galaxies, but I’ve never heard mention of other galaxies having bubbles. I don’t suspect we’re unique, though (wouldn’t it be something if we were).

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