Binary black hole in a spiral galaxy

NGC 3393 has clear signs of a recent merger:

But:  how did that merger produce a close black hole pair in the core (seen here in Xrays, Fabbiano et al) without destroying the disk?

The CHANDRA press release:

http://chandra.harvard.edu/photo/2011/n3393/

and the full Nature paper:

http://www.nature.com/nature/journal/v477/n7365/full/nature10364.html