In today's universe, giant black holes are never naked--they're always cloaked by the bright starry centers of galaxies. But astronomers have long wondered which came first, the black holes or the stars. A new image of gas around the most distant black hole known suggests that it arose without many stars around it. The result is a tantalizing clue in the puzzle of how today's grand galaxies assembled.
Black holes and their host galaxies have a tight relationship: Regardless of their size, the central swarms of stars in galaxies are always about 500 times more massive than the giant black holes they contain (ScienceNOW, 5 June 2000). This correlation hints that black holes and their galaxies grew up in lockstep when the cosmos was young. But recently, a survey has found several quasars--bright cores of galaxies, powered by matter falling into a supermassive black hole--that existed less than a billion years after the big bang. That's not nearly enough time for massive shrouds of stars to accumulate, suggesting that black holes began to form first.
The new image reveals that one giant black hole may indeed have gotten a jump-start. A team led by Fabian Walter of the Max Planck Institute for Radio Astronomy in Heidelberg, Germany, used 27 large radio telescopes in New Mexico to spot warm carbon monoxide gas circling the most distant quasar yet found. "The quasar is so bright at other wavelengths that this is our only direct probe of the host galaxy," says study co-author Chris Carilli of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. The motions and extent of the gas suggest that the entire system contains about 50 billion times the mass of our sun. Still, that's just 10 to 50 times the mass of the central black hole, derived from earlier studies--leaving no room for a vast bulge of stars. The team's work will appear in a forthcoming issue of Astrophysical Journal Letters.
The image is striking, says astronomer Karl Gebhardt of the University of Texas, Austin. "Observations and theoretical models are beginning to push for supermassive black holes to come first," Gebhardt says. Still, Gebhardt notes that the carbon monoxide gas might not reflect the full mass of stars in the surrounding galaxy. Additional high-resolution images of distant quasars will show whether the technique is reliable, he adds.