According to the researchers, they said that “the eight eerie objects betray the past presence of quasars, the most luminous objects in the universe, whose powerful beams of radiation lend the clouds their ethereal glow.
The officials with the European space agency (ESA), which partners with NASA on the Hubble project wrote in a statement that, “in each of these images, a quasar beam has caused once invisible filaments in deep space to glow through a process called photo ionization.”
The officials added that “different elements like oxygen, helium, nitrogen, sulphur and neon in the filaments absorb light from the quasars and slowly re-emit it over many thousands of years.”
The quasars that lit up the eight gas clouds spotted by Hubble have since died out, the clouds lie far from the centers of their respective galaxies, so it took many thousands of years for the quasars beam to reach the clouds.
The first glowing green cloud that was found out was by a Dutch school teacher Hanny Van Arkel in 2007. Van Arkel found the cloud while participating in the galaxy online zoo project that asked volunteers to classify more than 1 million galaxies as they are catalogued in the Sloan digital sky survey.