[X] My Assistant

[SigurRosFan]

- http://www.ras.org.uk/index.php?option=com...id=984&Itemid=2

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The Local Hot Bubble
The Local Hot Bubble is a cool, old supernova remnant that envelopes the solar system and much more besides. It is not spherical, more like the shape of a bent hourglass or a peanut shell. The edge of the bubble is at least 91 light years away in the Northern fields, rising to 358 light years in the Southern fields.

Loop 1 superbubble
The Loop 1 Superbubble is a big, young, hot supernova remnant that is located approximately 684 light years away from the Sun and is about 895 light years in diameter.
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[dvandorn]

Well, OK -- though the Vela remnant is a lot more obvious and detectable than the bubbles we're talking about. The local bubble that we're currently within is cold, almost completely undetectable unless you cancel out *all* radiant energies from other stars, etc., and the hotter bubble pushing in on it is almost as difficult to detect.

We're not talking about pretty, quite dense (relative to the local bubbles) and quite detectable supernova remnants, here. We're talking about almost completely invisible currents of remnant gas and dust. Where they interact, and where they sit nearby other stars, they are so tenuous that the starlight completely obliterates any detectability. That's a far cry from the Vela nebula, which still visibly shines in reflected starlight.

We're also talking about bubbles that are hundreds of light years in diameter. How long does it take for a supernova remnant to expand that far? Only 20 or 30 million years? Expanding debris shells from supernovae are only accelerated at the very beginning, recall, and are subject to decelaration due to the pull of the neutron star / black hole supernova remnants. They may start expanding at near-relativistic speeds, but they slow down as time goes on.

I guess I'd like to see some numerical analyses on these things before pronouncing them relatively recent newcomers to this neighborhood of the Milky Way.

-the other Doug