NASA’s Hubble space telescope has captured images of eight massive green wispy gas clouds tens of thousands of light years away. These eight objects reveal the past presence of quasars, which are the bright masses of light and energy and arguably the most luminous objects in the universe. The green clouds of gas get their ethereal glow from the powerful radiation beams of quasars, NASA said in a statement.

Hubble Snaps Rare Images Of Quasar Ghosts

Gas clouds were formed during merger of galaxies

In each of the eight images, a quasar radiation beam has caused once-invisible filaments in deep space to light up through a process called photoionization. The European Space Agency (ESA) scientists believe that these long tails of gas were formed during a violent merger between galaxies. Nitrogen, oxygen, sulfur, neon and helium in the filaments absorb light from a quasar and re-emit it over thousands of years.

A quasar is an incredibly bright region that surrounds a supermassive black hole at the center of a galaxy. As dust and gas fall towards the black hole from its surrounding “accretion disk,” it heats up to extremely high temperatures, according to Space.com. It results into a quasar, which emits jets of high-energy particles and radiation into space.

The quasars that brighten up the eight gas masses spotted by Hubble space telescope have since died out. The gas clouds are far away from the center of their respective galaxies. So, the radiation and particles emitted by quasars took thousands of years to reach the gas clouds. Though the quasars have died out, the green clouds will continue to glow for a long time before they too fade.

Hubble turns 25 on April 24th

These gas clouds appear green due to ionized oxygen. The first gas cloud of this type was spotted by Dutch schoolteacher Hanny van Arkel in 2007. She discovered it while participating in the online Galaxy Zoo, a project that asked volunteers to classify over a million galaxies cataloged in the Sloan DigitalSky Survey (SDSS).

Hubble space telescope will be celebrating its 25th anniversary on April 24th. NASA will release a documentary to commemorate the event. Hubble was launched into orbit in 1990.