KISSIMMEE, FLORIDA—In 2003, astronomers took a snap of quasar—the superbright core of a distant galaxy—called SDSS J1011+5442. A year ago, they took another look at it and found to their astonishment that it had all but disappeared. Its bright beacon—a supermassive black hole that is heating the gas around it to millions of degrees—seemed to have switched off, leaving J1011 looking like just any other galaxy.
The observers, using the Sloan Digital Sky Survey (SDSS), a 2.5-meter telescope at Apache Point, New Mexico, sought out observations by other telescopes and found that the abrupt change had taken place over the course of just a few years after 2010. Over the past year, the team has found a dozen other quasars that similarly blinked out, earning them the name “changing-look” quasars. “These are classified by eye. You can see it happen,” says team leader Jessie Runnoe of Pennsylvania State University, University Park.
Fellow astronomer and team member John Ruan of the University of Washington, Seattle, told the American Astronomical Society meeting here today that he had previously assumed changes to something as big as a quasar would take tens of thousands if not hundreds of thousands of years. Ruan and his colleagues considered a number of possible causes for the abrupt change. First, a dust cloud could have moved in the way and blocked the light. But this would have taken much longer than a few years for something as big as a quasar. They also thought that in 2003 the galaxy could have emitted a brief flare as it tore apart a star and swallowed it up, but other observations showed the quasar was still bright for years after 2003. So they finally concluded that J1011 simply ran out of fuel.
The black holes at the heart of quasars have disks of gas and dust orbiting around them, and it’s the innermost part of the disk that burns brightest just before it is sucked in. J1011 simply consumed its entire inner disk, leaving a signal that looks just like a normal galaxy. “If you drain the inner part of the disk, it shuts everything down,” Runnoe says.
“It’s definitely an interesting result. It adds to a picture of quasars being highly variable systems on a range of timescales,” says astronomer Kevin Schawinski of the Swiss Federal Institute of Technology in Zurich, who is not involved in the work. Recent theoretical and observational work has suggested that quasars “flicker” on scales of a few hundred thousand years. “What this work shows is that quasars can change pretty dramatically on even shorter timescales of a few years.”
The SDSS team is now keeping its eyes peeled, just in case the inner disk of one of their changing-look quasars fuels up and turns the lights back on again.