V404 Cygni

Astronomers believe that the wobble is caused by the Lense-Thirring effect due to warping of space/time by the huge gravitational field in the vicinity of the black hole.

[9] This discovery was evidence that V404 Cygni formed with a minimal black hole natal kick on the order of less than 5 km/s.

A worldwide observing campaign was commenced and on 17 June ESA's INTEGRAL Gamma-ray observatory started monitoring the outburst.

INTEGRAL was detecting "repeated bright flashes of light time scales shorter than an hour, something rarely seen in other black hole systems", and during these flashes V404 Cygni was the brightest object in the X-ray sky—up to fifty times brighter than the Crab Nebula.

[11] A detailed analysis of the INTEGRAL data revealed the existence of so-called pair plasma near the black hole.

[23] A follow-up study of the 2015 data found a coronal magnetic field strength of 461 ± 12 gauss, "substantially lower than previous estimates for such systems".

Rare X-ray outburst from a stellar-mass black hole in the binary system V404 Cygni. Video on YouTube
A visual band light curve for V404 Cygni. The main plot shows the large variations during the 2015 outburst, and the inset shows the short timescale variations. Adapted from Rodriguez et al. (2015) [ 20 ] and Martí et al. (2016) [ 21 ]