Why Did We Think They Would Be Galactic?
In the beginning, astronomers believed gamma-ray bursts (GRBs) must
originate from inside our Galaxy because of the tremendous
amount of energy that was involved. Keep in mind that what is measured
by a detector near Earth is only a
small percentage of the actual energy emitted by the source. The total
energy produced is proportional to the distance2 away that
the object is. [If we assume the GRB radiates uniformly in all
directions, then Total Energy = (Flux)(4pi)(r2), where
the flux is what is actually measured and r is the distance away from
the object that the measurement was assumed to be taken.] An object in
our Galaxy has a small distance compared to
an object outside our Galaxy. If we were to assume that this energy
measured comes from outside the Galaxy, the total energy calculated
would be beyond anything we can imagine!
But we now know that, in fact, GRBs come from other galaxies...