This all-sky image was obtained by ESA's Integral gamma-ray observatory during four years of operations and provides an important step towards estimating how many black holes there are in the Universe.
The sources in this image were artificially blurred and the colour map was stretched to make both strong and weak sources readily visible. The concentration of sources along the mid plane of the image is due to neutron stars and stellar mass black holes in our Galaxy, while the majority of sources located far away from the Galactic plane are super-massive black holes in other galaxies. The Cosmic X-ray Background is composed from the emission of tens of millions of similar objects much further away from us.
Superposed is an Earth image by ESA/EUMETSAT’s Meteosat satellite. Using the Earth as a shield to block the emission from the population of distant black holes astronomers precisely gauged the X-ray and gamma-ray background. An angular size of the Earth as seen from Integral during actual observations was smaller than shown in the image.