Integral sees a ‘quiet’ Galactic Centre

This mosaic image, built with exposures obtained by the IBIS/ISGRI instrument on board ESA’s Integral gamma-ray observatory in April 2006, shows the Galactic centre region, an area of the sky supposed to host a gigantic black hole and characterised by the presence of a variety of hard X-ray and gamma-ray point sources. Due to the variability these sources possess on all time scales, the region never looks exactly the same.

Surprisingly, the sources were ‘off’ around the time of the observation (including the normally bright well-known black-hole candidate and micro-quasar 1E 1740.7-2942), displaying an unusually ‘quiet’ galactic centre. This is a very different view from those obtained on the long-term average.

The sources and the positions marked in white are almost permanently visible, while those marked in red are known ‘transient’ sources, that is sources more often ‘off’ than ‘on’.

The source called 1E 1740.7-2942 is normally the brightest source in the Galactic Centre region. It is a well-known black-hole candidate, as well as a micro-quasar source. The massive black hole at the very centre of our Galaxy, Sagittarius A* (or Sgr A*), is very close to source marked as ‘1’, corresponding to IGR J17456-2901.

The image covers a sky area of 4.3x2 degrees, and it is centred on (0, -0.5) degrees in Galactic coordinates.