kilonova

History

Theory predicted kilonovae in 1998, but they were first observed in 2017, simultaneously recording gravitational waves from the same event.

How it works

The impact generates a cloud of superheavy atomic nuclei, which quickly decay, glowing due to radioactivity — like the flickering embers of a campfire. This glow is what astronomers observe.

History

Theory predicted kilonovae in 1998, but they were first observed in 2017, simultaneously recording gravitational waves from the same event.

How it works

The impact generates a cloud of superheavy atomic nuclei, which quickly decay, glowing due to radioactivity — like the flickering embers of a campfire. This glow is what astronomers observe.

History

The kilonova concept was proposed in 1998 by Li-Xin Li and Bohdan Paczyński, who predicted bright radioactive glow from matter ejected during neutron star mergers, calling it a 'macronova' or 'r-process supernova'. The term 'kilonova' later stuck by analogy with nova and supernova. The first observation occurred on August 17, 2017, when the LIGO and Virgo detectors registered gravitational waves from the merger of two neutron stars (GW170817), and over the following hours and days, observatories worldwide detected the electromagnetic source AT2017gfo, unambiguously identified as a kilonova.

How it works

During the merger of neutron stars, tidal forces eject part of the material at high speed. This material is neutron-rich (neutron density reaches 10²⁰ cm⁻³) and undergoes rapid neutron capture, forming elements up to uranium and thorium. Unstable isotopes then decay, releasing energy: beta decay and nuclear fission heat the shell to temperatures around 10,000 K, causing thermal emission in the optical range. The light curve (brightness over time) has a characteristic hump with a rise time of about a day and subsequent decline following a power law. Gravitational waves from the merger are described by Einstein's equations of general relativity, and accretion disk dynamics by magnetohydrodynamic equations.

Open problems & fun facts

What is the contribution of kilonovae to the galactic content of heavy elements compared to other sources (supernovae, collapsars)?; The equation of state of neutron star matter is unknown, affecting ejecta parameters and luminosity.; The merger rate of neutron stars remains uncertain, limiting the accuracy of predictions for the chemical evolution of galaxies.; A more detailed understanding of ejecta opacity, especially for lanthanides, is needed to compare models with observations.

💡 If you are holding a gold ring, remember: the atoms of that gold were likely born in a kilonova — the collision of two neutron stars long before the formation of the Solar System.