Discovery of relativistic outflows in Seyfert galaxies

Outflows are ubiquitous in AGNs, manifested by blue-shifted absorption lines in the soft X-ray and UV bands. In the past ten years we have made significant progress in understanding the physical conditions in AGN outflows, now allowing us to ask important astrophysical
questions. Where do the outflows originate from; how much mass, energy and momentum do they carry; how do the observed properties of outflows relate to the predictions of theoretical models? Do outflows make efficient agents of feedback invoked by theoretical models to solve a range of astrophysical problems?
Recent discovery of ultra-fast outflows with relativistic velocities has added another intriguing aspect to this field. These outflows are manifested by blue-shifted absorption lines in the hard X-ray band, produced mostly by highly ionized iron.  While the low velocity outflows
can be produced by radiation pressure, theoretical models have difficulty producing ultra-fast outflows in relatively low-luminosity AGNs; magneto-hydrodynamics may be important. Observations of relativistic outflows therefore have far-reaching consequences to our
understanding of disk winds and perhaps accretion disks themselves. 
We recently discovered relativistic outflows in the soft X-ray band with multiple absorption lines of multiple elements. These detections are robust and alleviate earlier concerns about statistical significance of lines in the hard X-ray band. This opens up an exciting new possibility of in-depth study of relativistic outflows. I will present an overview of AGN outflows, highlighting the discovery of relativistic outflows, and discuss the opportunities and challenges offered by them.