SIMULATION
The following simulation allows one to hear
the sounds of gravity waves due to the formation of neutron stars at
cosmological distances…or back to the epoch of early star formation. As the
simulated gravity waves in this study will have frequencies in the range 20 -
600 Hz, then we are able to hear such emissions as audible sound. These sounds
have been termed "popcorn noise" due to their similarity to the sound
of crackling popcorn.
There are several interesting features to
this simulation. The cosmological model and the total rate of neutron star
formation combine to produce the amplitude and red-shifted frequency. In fact,
in this simulation the only variable is the distance of emission from Earth
(measured in red-shift).
The following model parameters were used:
- COSMOLOGY-
Einstein-de-Sitter
- NEUTRON STAR FORMATION RATE - Madau, Pozetti & Dickenson (1998) have provided two SFR
models fitted to the observational data. Model 1, Y1, assumes little dust extinction at large
redshifts and model 2, Y2, assumes a z-dependent dust opacity with a
colour excess E (B -V ) that rises as (1+z )2.2. In this work we restrict our simulation to the
high dust extinction SFR model, Y2,
in which half of the present-day stars were formed at z > 2.5 and were
enshrouded by dust.
- GRAVITATIONAL WAVEFORMS - We
use the results from Zwerger & Müller (1997). These authors produced a
set of 78 simulated waveforms based on the dynamics of axisymetric
rotational core collapse using a post-Newtonian approach. They found that
their computed waveforms can be categorized as Type I (spike + ringdown),
Type II (several distinct spikes) and Type III (large positive and smaller
negative wave amplitudes just before and after bounce but no distinctive
spike). Each type is characterized by the adiabatic index of the core
material and core rotation. Type I signals are produced by a
"soft" equation of state and Type II by a "stiff"
equation of state. Type III signals are characteristic of a soft equation
of state and a rapidly rotating core. We use three GW waveforms from ZM97,
based on an initially rigidly rotating polytrope. A Type I waveform,
A1B3G3, a Type II waveform, A1B3G1, and a Type III waveform, A1B3G5, were
selected as representative of the three types.
- SIMULATION- Our
calculations for the potentially detectable rate of neutron star formation
throughout the Universe using the above model parameters yields a rate of
35 events per second.
To hear
approximately10 seconds of a simulation using a particular waveform:
Type I : Sound
Type II Sound
Type III Sound
We have produced a
simulation using a random sample of the three waveforms. To hear approximately
20 seconds of a randomly mixed simulation:
Mixed: SimSFR2Mixed.wav
REFERENCES
Madau P., Pozetti
L., Dickenson A., 1998, ApJ, 498, 106.
Zwerger T., Müller
E., 1997, A&A, 320, 209.