Its hard to believe they don't know why or how these formed.
But since it takes around 25,000 years for us to see them from Earth and they're such developed forms (add at least another 25,000 years) it seems more likely they are continuous features rather than being the residue of some intermittent event.
I think there are bubbles like this in all formed galaxies.

Thanks for posting all this stuff with the ongoing story. It makes for more interesting reading! The previous section on eta carinae and the carina nebula had examples of what might also be Fermi Bubbles from less-developed sources.

Yeah I thought it was pretty amazing that we're just finding out about such large-scale--albeit diffuse--features of the galaxy! Who knows what else we're missing (well like all that unaccounted-for "dark matter" for instance)?

Even 50,000 years would be something of an eye-blink in astronomic time, but the NASA article (this one: http://www.nasa.gov/mission_pages/GLAST ... cture.html) said the bubbles may be "only a few million years old"--although it didn't say why they thought that. According to this: http://en.wikipedia.org/wiki/Galactic_c ... population , the Milky Way is thought to undergo a large starburst every 500 million years or so (we're supposed to be due for one in 200 million years) when the accumulating gas and dust around the core reaches critical density, so since the last should have been about 300 million years ago, the bubbles might not be from that, but that's not to say that there wouldn't be intermittent smaller outbursts on a somewhat regular basis as Sgr A* swallows individual stars, nebulae, and stellar black holes that drift too close.

And since the black hole is always there spinning, whether or not it's active, I'd think a large-scale magnetic field that could shape the bubbles could be a fairly permanent feature, even if its strength may vary depending the hole's activity level--but that's all total conjecture by my totally unqualified self!

The bubbles could be a way to conserve and maintain the dynamic energies of the center core, balancing the excessive energy of the disk with that of the black hole.
This buffer would keep a more constant rate to the structure. It would keep things regular and periodic.

And it's important to stay regular! :D

Anyway that all sounds good as far as *I* know. ;)

"Dark Matter" indeed !
(also unqualified)

The problem with Dark Matter is that once you figure out what it is, it's no longer dark! Or is it? Oh heck I dunno.

I don't think that dark matter exists.
When you find someone looking for dark matter you should just pat them on the head and let them keep looking. If they actually think that something they've never seen exists because their math tells them that it must, then you should just humor them.
(mostly unqualified speculation)

It's the luminiferous aether of today!

We might never REALLY understand anything. All the answers are wrong except the current approximation of the truth. Our senses are approximate and limited and so are ideas, even about perfection and absolutes.
But the good thing is that we keep getting closer to the truth anyway.

http://bigkahunaphotoshop.freeservers.com/photo4.html

This is the Fermi Bubble picture with a modification to illustrate what might actually be happening. It would explain how there is a black hole in the center (and why) and how a galaxy might actually be a dynamic structure more like an engine that would move on its own. No need for any mysterious dark matter!

Aww, but "dark matter" is sexy! It gets movies made about it and everything!