Stellar Explosions & Extreme Stars
Kilonovae
A kilonova is the glow that follows the collision of two neutron stars, powered by freshly made heavy elements.
It was first confirmed in 2017, alongside gravitational waves, and is a leading candidate site for making elements such as gold.
- Observe
A fast-fading source that starts blue and turns red over days.
- Measure
Brightness and spectra in ultraviolet, optical and infrared light.
- Model
Models of radioactive heating from the decay of heavy elements in the merger debris.
- Explain
Two neutron stars merged and made heavy elements.
What is it?
When two neutron stars, or a neutron star and a black hole, spiral together and merge, a small fraction of neutron-rich material is flung outward. Radioactive decay of the heavy nuclei formed in that debris heats it and makes it shine. That afterglow is called a kilonova, named because its peak brightness is roughly a thousand times a classical nova.
The picture is supported by the 2017 event GW170817, but it rests on one well-observed case. How much of the universe's gold and platinum comes from kilonovae, compared with other sources such as rare types of supernova, is still an active research question.
How does it happen?
- Stage 1Two neutron stars orbit each other
- Stage 2They spiral in and mergeGravitational waves are emitted
- Stage 3Neutron-rich debris is ejected
- Stage 4Radioactive decay powers the glowKilonova over days to weeks
What do we actually observe?
- Fast evolution
- The source brightens quickly and fades within about a week or two, faster than a typical supernova.
- Color change
- It shifts from blue to red and then to infrared as the debris expands and cools.
- Companion signals
- The 2017 event also produced a short gamma-ray burst and gravitational waves.
How do scientists detect it?
- Gravitational-wave detectors. LIGO and Virgo caught the merger signal first in 2017, which told telescopes where to look.
- Gamma-ray satellites. Fermi and INTEGRAL saw the short gamma-ray burst about two seconds later.
- Optical and infrared telescopes. Dozens of observatories followed the fading glow, which was designated AT 2017gfo.
Because the gravitational-wave signal, the gamma-ray burst and the light all arrived from the same place in the sky, astronomers could tie the glow directly to a neutron-star merger. This is called multi-messenger astronomy.
Why does it matter?
- Heavy-element formation: the light showed signs of very heavy nuclei being made, supporting the rapid neutron-capture process.
- Gravitational waves: kilonovae give the light counterpart to signals that otherwise have no image.
- Nuclear physics and expansion: mergers help constrain how matter behaves inside neutron stars and give an independent way to measure cosmic expansion.
The SpaceWeatherTracker connection
SpaceWeatherTracker follows an observe, measure, model and explain approach. Kilonovae are a clear example: one event was observed with several kinds of instruments, and models were tested against it.
This is an explainer. SpaceWeatherTracker does not show live data for this phenomenon; see the “Space Phenomena Now” section on the hub for what is currently monitored.
Related phenomena
Primary family: Stellar Explosions & Extreme Stars
Kilonovae: common questions
Is a kilonova the same as a supernova?
No. A supernova is the death of a single star or white dwarf. A kilonova follows the merger of two compact objects and is fainter and fades much faster.
Do kilonovae make gold?
Evidence from the 2017 event suggests they make heavy elements such as gold and platinum. How large their share of the universe's supply is remains under study.