Chapter 4: Lizard Heart

Gravitational Waves from Binary Neutron Stars

In this model, two 1.4 solar-mass neutron stars (not drawn to scale) are in a perfectly circular orbit, viewed here at an oblique angle. The angle between the orbital plane and the line of sight can be changed with the pop-up menu near the top right-hand corner of the diagram. By adjusting the angle with the orbital plane, you can shift between sampling waves with purely linear polarisation (at 0 degrees) to waves with purely circular polarisation (at 90 degrees).

The orbit obeys Kepler’s Law: the period squared is proportional to the separation cubed. For example, bringing the neutron stars closer by a factor of 4 will reduce the period by a factor of 8. You can click on (or drag) a point within the upper panel to make the orbit pass through that point. If the new orbit is too large to fit, or too small to see clearly, the diagram will be re-scaled; the time scale is also adjusted when necessary.

The lower panel shows (greatly exaggerated) the effect of the gravitational waves on an initially circular ring of free-floating particles, far from the system, lying in a plane perpendicular to the line of sight. (The actual size of the effect at 100 light-years is given below.) The black trace records the horizontal stretching and compression of the ring; the scales are adjusted as necessary, but the portion of the trace displayed at any given moment is always shown at a uniform scale.

You can read about the mathematical details behind this model here.

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Note: This model is based solely on General Relativity. In Diaspora, other effects — arising from the novel’s invented cosmology — accelerate the decay of the binary neutron star Lacerta G-1, but those effects are not shown here.

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Diaspora / Chapter 4: Lizard Heart / created Saturday, 25 October 1997 / revised Tuesday, 23 June 1998
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