Dead quasar illuminates black holes

The green Voorwerp in the foreground remains illuminated by light emitted up to 70,000 years ago by a quasar in the center of the background galaxy, which has since died out. (Credit: William Keel, Anna Manning/WIYN Observatory)

Scientists say the object, known as Hanny’s Voorwerp and discovered by Dutch schoolteacher Hanny von Arkel as part of the Galaxy Zoo citizen science project, is a large cloud of glowing gas illuminated by the light from a quasar—an extremely energetic galaxy with a supermassive black hole at its centre.

The twist, described online in the Astrophysical Journal Letters, is that the quasar lighting up the gas has since burned out almost entirely, even though the light it emitted in the past continues to travel through space, illuminating the gas cloud and producing a sort of “light echo” of the dead quasar.

“This system really is like the Rosetta Stone of quasars,” says Kevin Schawinski, an astronomer at Yale University, co-founder of Galaxy Zoo, and lead author of the study.

“The amazing thing is that if it wasn’t for the Voorwerp being illuminated nearby, the galaxy never would have piqued anyone’s interest.”

The team calculated that the light from the dead quasar, which is the nearest known galaxy to have hosted a quasar, took up to 70,000 years to travel through space and illuminate the Voorwerp—meaning the quasar must have shut down sometime within the past 70,000 years.

Until now, it was assumed that supermassive black holes took millions of years to die down after reaching their peak energy output. The Voorwerp suggests, however, that the supermassive black holes that fuel quasars shut down much more quickly than previously thought.

“This has huge implications for our understanding of how galaxies and black holes co-evolve,” Schawinski says.

More.......