Scientists have recently discovered wispy, goblin-green objects which are supposed to be the ephemeral ghosts of quasars – extremely bright masses of energy and light – that flickered to life and then faded.
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. The most active galaxy cores are called quasars, where in-falling 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, according to a statement by NASA.
“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 do,” said Bill Keel of the University of Alabama, Tuscaloosa.
One possible explanation, according to Keel, is that pairs of co-orbiting black holes are powering the quasars. This could change their brightness, like using the dimmer switch on a chandelier.
The quasar beam caused the once invisible filaments in deep space to glow through a process called photoionization. Oxygen atoms in the filaments absorb light from the quasar and slowly re-emit it over many thousands of years.
The green filaments are believed to be long tails of gas pulled apart like taffy under gravitational forces resulting from a merger of two galaxies. Rather than being blasted out of the quasar’s black hole, these immense structures, tens of thousands of light-years long, are slowly orbiting their host galaxy long after the merger was completed.
“We see these twisting dust lanes connecting to the gas, and there’s a mathematical model for how that material wraps around in the galaxy,” Keel said. “Potentially, you can say we’re seeing it 1.5 billion years after a smaller gas-rich galaxy fell into a bigger galaxy.”
The ghostly green structures are so far outside the galaxy that they may not light up until tens of thousands of years after the quasar outburst, and would likewise fade only tens of thousands of years after the quasar itself does. That’s the amount of time it would take for the quasar light to reach them. Galaxy mergers would also trigger the birth of a quasar by pouring material into the central supermassive black hole.
In 2007, Dutch schoolteacher Hanny van Arkel found the first “green goblin” type of object. She discovered the ghostly structure in the online Galaxy Zoo project.
The images were taken using Hubble Space Telescope, which is a project of international cooperation between NASA and the European Space Agency.
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