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## Black Hole Waveforms

### Distorted Black Hole

This figure shows the actual waveform calculated from supercomputer simulations.
After the initial growth in the strength of the wave, there is a decaying signal of a
definite frequency and damping time. This is the "ringing mode", or normal
mode of the black hole. The ringing mode frequencies are known from
perturbation calculations of black holes, and depend on the mass and spin
of a black hole. The calculations show that the ringing mode of black hole
would be excited when distorted. The resulting signal, when detected
by LIGO, would allow astronomers the mass of the disturned black hole.
### Rotating Black Hole

A similar calculation was performed for a distorted,
rotating black hole. The waveform is very similar to the non-rotating case,
but the frequencies are slightly different. In this case, an accurate
detection would allow astronomers to determine not only the mass, but also
the spin of the black hole.
### Colliding Black Holes

This is the result of a calculation of two equal mass black
holes colliding head-on. Very little radiation is
emitted until the two black holes collide, forming a distorted larger black
hole that then "rings" down to a quiet, spherical hole. Again, the signal
would allow astronomers to determine the mass and spin of the final hole
created in this process.
Notice the very strong similarity between the three waveforms presented.
Taken together, these three waveforms show that a characteristic signal is expected
from almost any black hole process. In particular, astronomers and physicists hope to detect
the waveforms associated with all stages of a black hole collision: from when the holes spiral
into each other to their merger moments later.

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#### Copyright, 1995: Board of Trustees, University of
Illinois

*NCSA. Last modified 11/7/95*