Ok, in Stephen Baxter's "Moonseed" he mentions extremal black holes (something which I had never encountered before, oddly enough); running a search, all I've found is that they are essentially a/the ground state for black holes.

This seems to fly on the face of Bekenstein-Hawking radiation: black holes evaporate (where a b.h. where m=20 sol would have an evap. time of 1.2*10^70 yr., whereas m=2 sol yields t=1.2*10^67 yr.).

The real boggle, though, is that by definition they are massless. I understand that this is due to black holes' mass being proportionate to their radius in 6 dimensions, but fail to see how they could continue their existence once brought to their ground state r=0.

Can anyone tell me how a black hole could deviate from black body to extremal, and how it could maintain such a state? So far, all I can gather is that this has something to do with intersecting m-branes. :-(

• Massless Black Hole - storm15918 - June 13, 2008 - 20:12 UTC