The rotating wind of the quasar PG 1700+518

What goes round Two groups this week present observational evidence to support long-held but unverified theories tackling similar astrophysical problems: the dissipation of angular momentum from accretion disks. Stars form when interstellar gas clouds collapse under the influence of gravity. As these clouds begin to collapse, any rotation will be magnified because of the conservation of angular momentum — like an ice-skater in a spin. If unchecked, the rotation would be too rapid to allow star formation and theorists suggest that the young stars lose rotational energy via material outflow induced by magnetic fields. Now there are observations to support the theory: Chrysostomou et al. use circular polarimetry to reveal helical magnetic fields in the outflow of the young star HH 135–136. There are theoretical grounds for believing that active galactic nuclei outflows originate as disk winds from a rotating accretion disk around a supermassive black hole. Verification of this idea has proved elusive. Now Young et al. use spectropolarimetric tomography to establish that quasar winds are in fact rotating. The quasar PG 1700+518 produces a wind spinning at about 4,000 km per second, rising nearly vertically from the disk.