LIGO detected the first gravitational wave signal in 2015, shown below. Strain i
ID: 1996903 • Letter: L
Question
LIGO detected the first gravitational wave signal in 2015, shown below. Strain is the change in the length of the interferometer arm (2.5 miles). A strain of 10-21 means that the interferometer arm length changed by 2.5 x 10-21 miles! This gravitational wave signal was produced by a binary system of black holes. The following questions ask what this binary system was doing to produce various parts of the gravitational wave signal seen below.
a) Compare the portion of the signal labelled "A" to the portion labelled "B". What was the system doing differently to produce the "A" signal vs. the "B" signal? How do you know?
b) For the portion of the signal labelled "C", what was the system doing? How do you know?
Explanation / Answer
a) Signal "A" indicates that the frequency of rotation of the binary system (as the system of black holes were orbiting around one another) is higher than that at the location of signal "B".
b) At the position of signal "C", the signal starts disapperaing that indicates that the orbiting binary system have merged into one and hence no longer rotating to produce gravitational waves.
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