NASA detects rare ‘double quasar’
What burns brighter than a quasar, the hungry, supermassive black holes that outshine entire galaxies as they voraciously gobble up everything in reach? How about a ‘double quasar’? Astronomers used NASA’S Hubble Space Telescope to peer 10 billion years into the cosmic past, where they detected two gargantuan quasars on the verge of colliding. Sitting at the centres of their respective galaxies, these hungry quasars have less than 10,000 light years of breathing room between them, putting them far closer to each other than Earth’s Sun is to the centre of the Milky Way, about 26,000 light years away. To ground-based telescopes the quasar neighbours look like a single object, and one day, thanks to the unstoppable collision of their home galaxies, they will become one. This is not the first double quasar that astronomers have ever detected. More than 100 have been discovered to date. However, the ancient pair of blazing lights is by far the oldest double quasar in the known universe – and it’s not alone. Researchers reported the detection of a second double quasar, also dating to 10 billion years ago. “We estimate that in the distant universe, for every 1,000 quasars, there is one double quasar,” said Yue Shen, associate professor of astronomy at the University of Illinois at Urbana-champaign. “So finding these double quasars is like finding a needle in a haystack.” Researchers focused their search on the distant universe, as star formation is thought to have peaked in the universe about 10 billion years ago, and galactic mergers were much more common then. These mergers funnelled huge amounts of matter towards the black holes lurking in the cores of galaxies. As those black holes sucked in matter at near-light speed, they released a flood of radiation, becoming quasars. Quasars can outshine large galaxies, though their brightness may fluctuate every few days, weeks or months, depending on how much matter they’re gobbling up at the time. Because of this finicky eating schedule, a double quasar may appear to ‘jiggle’ in place when one member of the pair brightens or dims, while the other remains static. With the help of the Gaia space observatory and Sloan Digital Sky Survey, researchers targeted several jiggling quasars in the distant universe, then zoomed in using the Hubble Space Telescope. Two of these jiggling light sources turned out to be ancient double quasars, both flickering towards their inevitable collisions.
Studying merging quasars can help scientists understand the nuances of galaxy formation – and their destruction. As quasars grow, their radiation can generate powerful winds that may ultimately blow all of the star-forming gas out of their way. When this gas is gone, star formation ends, and the galaxies that house the quasars enter early retirement, slowly waiting for all their old stars to burn out and fade away.