The morning after, Vladimir Lipunov woke up, opened his computer and saw something nobody had ever seen. It was 2017. Overnight, a 4-kilometre detector had felt the trace of two neutron stars colliding. Lipunov, an astrophysicist who had spent decades modelling binary stars, counts himself among the first people to look at it.
The glow that follows such a collision has a name: a kilonova. Before that morning, he says, no one had seen one.
Here is why a jeweller should care. At the very end of the episode, almost as an aside, Lipunov says the gold and platinum on a woman's hand are the metals that formed in this merger. Not a trace of them, he says: all the heavy elements of the periodic table came out of a kilonova's expanding cloud. He doesn't build the case at length. He says it as a fact of the sky and moves on. But the picture he leaves is hard to shake.
Start with the object. A neutron star, in his telling, is one gigantic atomic nucleus, about ten to the power of 58 neutrons and protons held together by gravity. Ordinary heavy nuclei are fragile. Pack too many protons into one and the electric push between them wins, because the nuclear force reaches only short distances. Such a nucleus lives for milliseconds. Only a star's worth of gravity keeps the lump from flying apart.
Now spin two of them together, faster and faster, until they merge. What remains is probably a black hole or a fat neutron star. But spinning is the problem. The centrifugal force beats gravity, so nature has to throw the fastest-rotating part away. That is about 1% of a star's mass, and it carries off 90% of the spin.
What is that thrown-out 1%? Nuclear matter, in the first microseconds. Protons and electrons have already "made friends" and become neutrons, and the free neutrons start fusing into heavy nuclei at speed. Lipunov calls it a rapid gluing together of heavy nuclei. That is where the heavy elements come from, he says.
Then it flies. The cloud expands at 100,000 kilometres per second. A supernova is ten times slower. A nova is ten times slower again.
A study in Nature in February 2024 by Yu-Han Yang and colleagues gives a sense of how these events are read today. The authors modelled an unusually long gamma-ray burst and found it gave rise to a kilonova rich in lanthanides, a family of heavy elements. The merger behind it was either two neutron stars or a neutron star and a black hole.
Lipunov's evidence for the whole picture is the 2017 detection. He had also spent years on the other end of it, as one of the people whose computer model of binary stars predicted such mergers. The team's "artificial Universe" had produced pairs of neutron stars long before anyone saw one. In 1995 his group published a map of the gravitational-wave sky, and they expected a few mergers a year within a distance their instruments could reach.
So the ring is a leftover. A few seconds of violence between two stars too small to see, and the debris came out at a third of the speed of light and travelled until it became part of a planet.
So, the girls, you see, have gold ones there, earring ones, all these, platinum there, especially the dress — those are exactly the metals that formed as a result of this merger.
так у девушек, видите, золотые там, сергиевые, эти все, платино там, особенно платье, это именно те самые металлы, которые образовались в результате этого слияния
— Vladimir Lipunov, Osnova, 61:56
The host's reaction was one word: mesmerising. Lipunov was still counting the speeds.
