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Gamma-ray Bursts

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... Imagine it!

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Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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Project Leader: Dr. Barbara Mattson
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This page last updated: Monday, 27-Sep-2004 11:26:11 EDT