Integral image before and after the outburst

These images show the patch of the sky where the black-hole binary system V404 Cygni is located, as observed with the IBIS instrument on ESA's Integral gamma-ray observatory. This system, comprising a black hole and a star orbiting one another, is located in our Milky Way galaxy, almost 8000 light-years away in the constellation Cygnus, the Swan.

On 15 June 2015, V404 Cygni started showing signs of extraordinary activity, something that had not happened since 1989. The renewed activity is likely caused by material slowly piling up in the disc, until eventually reaching a tipping point that dramatically changes the black hole's feeding routine for a short period.

The image on the left was taken on 19 May 2015, before the outburst: V404 Cygni is not present, and its position is marked with a cross. The image on the right, taken on 18 June 2015, shows V404 Cygni as the brightest source in the field.

The two sources Cygnus X-1 and Cygnus X-3, present in both images, are some of the brightest objects in the X-ray sky. Other transient sources are also present in both images, highlighting the great variability of the high-energy sky.

Acknowledgment: Carlo Ferrigno, Integral Science Data Centre, Geneva, Switzerland