Washington, April 3 (IANS): NASA's Hubble space telescope has clicked a set of wispy, goblin-green objects that are the ephemeral ghosts of quasars that flickered to life and then faded.

The glowing structures have looping, helical and braided shapes.

"They do not fit in a single pattern. The features offer insights into the puzzling behaviour of galaxies with energetic cores," said Bill Keel from the University of Alabama, Tuscaloosa.

These images reveal a set of bizarre, greenish looping, spiral and braided shapes around eight active galaxies.

The galaxies host a bright quasar that may have illuminated the structures.

"The ethereal wisps outside the host galaxy are believed to have been illuminated by powerful ultraviolet radiation from a supermassive black hole at the core of the host galaxy," NASA said in a statement.

The most active of these galaxy cores are called quasars, where infalling material is heated to a point where a brilliant searchlight shines into deep space.

The beam is produced by a disk of glowing, superheated gas encircling the black hole.

"The glowing filaments are telling us that the quasars were once emitting more energy, or they are changing very rapidly, which they were not supposed to," Keel noted.

One possible explanation is that pairs of co-orbiting black holes are powering the quasars and this could change their brightness, like using the dimmer switch on a chandelier.

Not coincidentally, galaxy mergers would also trigger the birth of a quasar by pouring material into the central supermassive black hole.