This artist's impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus. M. Kornmesser/ESO hide caption

itoggle caption M. Kornmesser/ESO

British cosmologist Stephen Hawking gives a talk to workers at Cedars-Sinai Medical Center in Los Angeles on April 9. Eric Reed/Cedars-Sinai/AP hide caption

itoggle caption Eric Reed/Cedars-Sinai/AP