Drag the sliders below to change the masses, spins, and tidal deformabilities of two merging neutron stars, and watch the gravitational-wave signal update live. As the stars spiral closer together they orbit faster and radiate more strongly, producing the rising-frequency, rising-amplitude “chirp” that detectors like LIGO, Virgo, and KAGRA actually measure.

Mass 1 (M_☉)

Mass 2 (M_☉)

Spin 1 (aligned, χ₁)

Spin 2 (aligned, χ₂)

Tidal deformability Λ₁

Tidal deformability Λ₂

This parameter combination pushed the post-Newtonian expansion past where it reliably converges, so the waveform was cut off early.

What am I changing?

Mass (M_☉)
How heavy each neutron star is, in multiples of our Sun's mass (M_☉). Neutron stars are the crushed-down cores left behind after a massive star explodes — even though each one is only about the size of a city, it can weigh more than our entire Sun. Heavier stars pull on each other more strongly, so they spiral together faster and produce a louder, quicker chirp.

Spin (χ)
How fast each star is spinning on its own axis, as a dimensionless number comparing its spin to its mass. Zero means not spinning at all. Real neutron stars can't spin arbitrarily fast — spin too quickly and a star would tear itself apart — but exactly how fast depends on what neutron stars are made of. Here, spin is "aligned," meaning it points the same way as the stars' orbit. Spin changes how fast the stars spiral together and subtly reshapes the wave.

Tidal deformability (Λ)
Unlike black holes, neutron stars are made of real matter, so each star's gravity stretches and squashes its partner as they get close — the same way the Moon causes tides on Earth, but far more extreme. A bigger Λ means a "squishier" star that deforms more easily, which drains orbital energy faster and speeds up the final moments before the stars collide. Measuring this effect is one of the best ways scientists have to figure out what neutron stars are actually made of.

This is a real (if simplified) physics model, not a cartoon: it integrates the TaylorT4 post-Newtonian equations of motion to 3.5PN order, with leading-order aligned-spin spin-orbit coupling and tidal corrections at 5PN and 6PN order, using the same coefficients as the LALSuite TaylorT4 implementation used across the field (Vines, Flanagan & Hinderer 2011; Vines & Flanagan 2013, for the tidal terms). What it leaves out: spin precession, higher-order spin-spin couplings, and the merger and ringdown themselves — it stops at the innermost stable circular orbit. The mass, spin, and tidal deformability ranges are representative of real neutron stars; the distance and orientation are fixed and the strain is shown in arbitrary, normalized units.