A unified framework for X-shaped radio galaxies
  We propose a radically different picture for X-shaped radio galaxies compared
to existing models as transition objects between cold mode accreting low
spinning retrograde black holes and low spinning prograde black holes. The
model explains their smaller average black hole masses, their general aversion
for cluster compared to isolated environments, the negligible difference in
spectral index between primary and secondary jets despite a time difference in
their formation, their absence among the most powerful radio quasars and radio
galaxies, and their connection to the elusive FRI quasar class, among others.
The key to their formation is cold gas accretion onto Schwarzschild black
holes.
