http://arxiv.org/abs/1904.07923
The warped spacetime around a black hole modifies the propagation of light and radio. A recent study predicted that light emitted from the immediate vicinity of a massive rotating black hole (BH) should be twisted, i.e. be imprinted with orbital angular momentum (OAM). This vorticity, caused by general relativity (GR) effects such as spacetime dragging and mixing, and gravitational lensing, enables new ways to study BH’s, including their rotation, and to test fundamental properties of GR itself. Here we report the detection of GR induced vorticity in radio emitted from the Einstein ring surrounding the shadow of the rotating ${\sim6.5\times10^9}$ solar mass BH in the core of the M87 galaxy, as observed by the Event Horizon Telescope (EHT). The M87 spiral spectra were identified in EHT intensity profile data by using a wavefront reconstruction technique enabling the recovery of the phase front. They reveal that the M87 BH rotates clockwise, with inclination $i=17^\circ$ and rotation parameter $a=0.9\pm0.1$, corresponding to a rotational energy of about $10^{64}$ erg. Our findings agree with published constraints and with analysis of the amplitude and phase profiles in fiducial pipeline images released by the EHT collaboration EHT4. Using structured light to make the first direct measurement of Kerr metrics and to reveal one of the most energetic astrophysical phenomenon ever observed, corresponding to the energy radiated by the brightest quasars over Gyr timescales, is a breakthrough that is likely to invigorate BH research and open new perspectives in astronomy and astrophysics.
F. Tamburini, B. Thidé and M. Valle
Thu, 18 Apr 19
62/75
Comments: 11 pages, 6 figures