Probing the spacetime around supermassive black holes with ejected plasma blobs

Millimeter-wavelength very-long-baseline-interferometry observations of the supermassive black holes in Sgr A* and M87 by the Event Horizon Telescope could potentially trace the dynamics of ejected plasma blobs in real time. We demonstrate that the trajectory and tidal stretching of these blobs can be used to test general relativity and set new constraints on the mass and spin of these black holes.

Figure 1

The radial motion of blobs with $e=2$ in the equatorial plane of a black hole with $a=0$ (solid line) and $a=0.999$ (dotted line).

Figure 2

Blobs with $e=10$ and radius $M$ launched with $\theta =0$ and $\theta =\pi /8$ as seen in the observer plane with the black hole located at (0,0). The observer’s time axis (in units of $M$) is indicated by the color bar. For a blob moving with $\theta =0$, the image is briefly lensed into a ring. The eccentricity of this ring can be used to test the no-hair theorem.

Figure 3

The projected position of blobs with $e=10$ launched at a variety of angles versus observer time.

Figure 4

The growth factor of the blob radius due to gravitational tide as a function of distance from the black hole for a blob moving with negligible angular momentum. The blob’s specific energy is $e=1.0001$, 1.001, 1.01, and 10 for the solid, dashed, dotted, and dot-dashed lines, respectively.

Figure 5

The growth factor of the blob radius as a function of distance from a spinning black hole for a blob trajectory with a negligible angular momentum. The black hole’s spin is $a=0$, 0.5, and 1 for the solid, dashed, and dotted lines, respectively. The blob energy is $e=1.2$ for all curves.