X ray Echoes Map a Black Hole s Disk

Some 3. 9 billion years ago in the heart of a distant galaxy, the tidal pull of a monster black hole shredded a star that wandered too close. Xrays produced in this event first reached Earth on March 28, 2011, when they were detected by NASA s Swift satellite. Within days, scientists concluded that the outburst, now known as Swift J1644+57, represented both the tidal disruption of a star and the sudden flareup of a previously inactive black hole. Now astronomers using archival observations from Swift, th