  Radio galaxy phenomenon is directly connected to mass accreting, spinning
supermassive black holes found in the active galactic nuclei (AGN). It is still
unclear how the collimated jets of relativistic plasma on hundreds to thousands
of kpc scale form, and why nearly always they are launched from the nuclei of
bulge dominated elliptical galaxies and not flat spirals. Here we present the
discovery of giant radio source J2345-0449 (z=0.0755), a clear and extremely
rare counter example where relativistic jets are ejected from a luminous and
massive spiral galaxy on scale of ~1.6 Mpc, the largest known so far. Extreme
physical properties observed for this bulgeless spiral host, such as its high
optical and infra-red luminosity, large dynamical mass, rapid disk rotation,
and episodic jet activity are possibly the results of its unusual formation
history, which has also assembled, via gas accretion from a disk, its central
black hole of mass >2 x 10^8 M_sun. The very high mid-IR luminosity of the
galaxy suggests that it is actively forming stars and still building a massive
disk. We argue that the launch of these powerful jets is facilitated by an
advection dominated, magnetized accretion flow at low Eddington rate onto this
unusually massive (for a bulgeless disk galaxy) and possibly fast-spinning
central black hole. Therefore, J2345-0449 is an extremely rare, unusual
galactic system whose properties challenge the standard paradigms for black
hole growth and formation of relativistic jets in disk galaxies. Thus, it
provides fundamental insight into accretion disk -- relativistic jet coupling
processes.
