Resource: Gamma-ray Burst Theories

Gamma-ray bursts were first detected in 1967, but scientists didn’t know what they were. It wasn’t until 1971 that astronomers identified these phenomenon as gamma-ray bursts (GRBs).

What are gamma-ray bursts? Why do they occur? Is there any predictable pattern to their appearance? These questions and many others have been under study by leading scientists and astronomers over the past 30 years.

Scientists know what GRBs are: flashes of gamma-ray light. What they don’t know is what causes them. Scientists are working on two primary theories, with the acknowledgement that a third possibility also exists.

• Hypernova (a super-supernova): A star has run out of fuel and this results in the creation of a black hole. In the process, the core of the star collapses and the outer shell explodes outward, releasing energy as a gamma-ray burst.
• Binary System: Remains of two exploded neutron stars, which previously exploded as supernovae, orbit each other. They lose energy and spiral inward. When they get close, gravity smashes them into each other, forming a black hole. We detect the energy released as a gamma-ray burst.
• Unknown: Scientist acknowledge the possibility that gamma-rays bursts may be caused by another factor that has not yet been considered or might not yet be discovered.

Gamma-ray bursts are violent explosions. They occur throughout the universe, and not just in our Milky Way galaxy as first believed. They occur two to three times a day at random places in our sky. The bursts are thousands of times brighter than a supernova. GRBs are beamed in tight little jets of energy instead of being sprayed in all directions.

GRBs can be in one of two categories: Short – lasting 2 seconds or less, or Long – lasting up to a minute or longer. The two types differ in more ways than just their duration. Spectroscopically, short bursts have more high-energy gamma rays than their counterparts do. According to Scientific American (December 2002), every time a gamma-ray burst occurs, a black hole is born.

Swift is a satellite designed by Penn State researchers and launched by NASA to study gamma-ray bursts. Launched in November of 2005, the satellite was named after the swift, a small, quickly moving bird. Catching a GRB is no easy task. The burst can appear from any direction without warning and can last for only a few milliseconds to just over a minute. So, the satellite has to move quickly and be in position to capture the data. According to NASA, no other satellite turns faster. In addition to GRBs, Swift searches and records other phenomena it observes in the sky.

The Swift satellite is comprised of three telescopes: the Burst Alert Telescope (BAT); the X-ray Telescope (XRT); and the Ultraviolet/Optical Telescope (UVOT). The BAT detects and locates the GRBs. Once one is identified, Swift repositions itself so that the other two telescopes can collect data on the afterglow of the burst. All the data is transmitted to earth and is available publicly within 30 minutes of the GRB detection.

• What are the three parts of the Swift satellite and what are their functions?
• Explain the two possible theories of gamma-ray bursts. What are they and how do they differ?
• Why are scientists optimistic about discovering more about gamma-ray bursts?