A massive stellar bulge in a regularly rotating galaxy 1.2 billion years after the Big Bang

Cosmological models predict that galaxies forming in the early Universe experience a chaotic phase of gas accretion and star formation, followed by ejection due to feedback processes. Galaxy bulges may assemble later via mergers or internal evolution. Here we present submillimeter observations (with spatial resolution 700 parsecs) ALESS 073.1, starburst galaxy at redshift z~5, when was 1.2 billion years old. This galaxy's cold forms regularly rotating disk with negligible noncircular motions. The rotation curve requires presence central bulge addition star-forming disk. We conclude massive disks can form more rapidly than predicted formation.