Prior to 1991, Most Astronomers Assumed That Gamma- Ray Bursts

Prior to 1991, most astronomers assumed that gamma- ray bursts came from neutron stars (with accretion disks) within the Milky Way Galaxy. How do we now know that this hypothesis was wrong?

A) Theoretical work has proven that gamma rays cannot be produced in accretion disks.
B) Observations from the Compton Gamma- Ray Observatory showed that gamma- ray bursts occur too frequently to be attributed to neutron stars.
C) Observations from the Compton Gamma- Ray Observatory showed that gamma- ray bursts come randomly from all directions in the sky.
D) We now know that gamma- ray bursts come not from neutron stars but from black holes.
E) Observations from the Compton Gamma- Ray Observatory allowed us to trace gamma- ray bursts to pulsating variable stars in distant galaxies.