Kilonova: GW170817 Neutron Star Merger
Relativity & Gravity arc, page 40 of 193. Back to The Pixelated Physics Universe
Who they are
Two neutron-star dancers collide in a burst that rains gold. Gravity and light set off together and arrived neck and neck.
Kilonova is a character of the Relativity & Gravity arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
On 17 Aug 2017 LIGO and Virgo detected gravitational waves from two neutron stars merging about 40 Mpc away. 1.74 ± 0.05 s later, gamma-ray burst GRB 170817A arrived. After a journey of about 130 million years, that tiny gap pins the speed of gravitational waves to the speed of light.
$$ \begin{gathered} \Delta t = 1.74 \pm 0.05\ \mathrm{s} \\ -3\times10^{-15} \le \frac{v_{gw} - c}{c} \le +7\times10^{-16} \\ \mathcal{M} = \frac{(m_1 m_2)^{3/5}}{(m_1+m_2)^{1/5}} = 1.188^{+0.004}_{-0.002}\ M_{\odot} \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $\Delta t$ | delay between the merger signal and the gamma-ray burst | s |
| $v_{gw}$ | speed of gravitational waves | m/s |
| $c$ | speed of light, 299 792 458 m/s (exact) | m/s |
| $m_1,\ m_2$ | masses of the two neutron stars | kg |
| $\mathcal{M}$ | chirp mass | kg |
| $M_{\odot}$ | solar mass, about 1.989 × 10³⁰ kg | kg |
Honest caveat: The 1.74 s gap includes the delay in emitting the gamma rays, which did not leave at the same instant.
Sources
- LIGO Scientific & Virgo Collaborations (2017) GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral, Phys. Rev. Lett. 119, 161101
- LIGO, Virgo, Fermi GBM & INTEGRAL (2017) Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A, Astrophys. J. Lett. 848, L13
Crossovers
Kilonova meets Graviton Whisper (Quantum Gravity / Force Carrier). Kilonova's waves and light arrived nearly together from 130 million light-years away. That tight timing limits how different the speed of gravitational waves can be from c. Graviton Whisper is glad: a massless graviton would travel at c.
Kilonova meets Choralis (Hellings–Downs Curve). Kilonova was one loud merger in LIGO and Virgo's band. Choralis hunts a quiet hum at nanohertz frequencies from many sources, perhaps supermassive black-hole binaries. The evidence for that hum is still short of 5σ.
Kilonova meets Trialpha (Hoyle State). Trialpha makes carbon in stars. Kilonova shows where much heavier elements come from: a neutron-star merger whose glow showed the signature of rapid neutron capture. Different furnaces build different parts of the periodic table.
Wear the lore
Concept keywords: GW170817 Neutron Star Merger, Kilonova, Relativity & Gravity, physics lore, Pixelated Physics