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How Far, How Powerful?
Getting from here to there

A detector records a gamma-ray burst. We measure the amount of energy that falls on this detector near Earth. How powerful was the event that we measure?
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First, we'll review how light falls off with distance. As we move away from a source of light, the energy we measure decreases.
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Next, we'll review Hubble's Law and the expansion of the universe. The further an object is from Earth, the faster it is moving away.
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We'll then see how fast a gamma-ray burst is moving away from us by measuring the Doppler shift of lines in its spectrum. From this, we'll find its distance from the Earth.
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Knowing the distance to the gamma-ray burst, the energy we measured, and the rate at which the universe is expanding, we'll find the power emitted in the event.

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.

The Imagine Team
Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

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