- Neutron stars that crash together in space forge valuable metals like silver, gold, and platinum.
- Some heavy periodic elements may be created almost exclusively by such cosmic crashes.
- Europium, one of the least-common elements in the universe, is a candidate and is used in TVs, lasers, and plastics.
- A neutron-star collision discovered through gravitational waves made about 1-5 Earths' worth of the europium, according to a new study.
In October 2017, astrophysicists announced a remarkable discovery: The first-ever detection of two dead stars smashing together.
The collision created gravitational waves, or ripples in spacetime, which were "heard" by the LIGO experiment. But the event — unlike merging black holes — threw off gobs of neutrons (essentially super-heavy-element barf).
This material almost immediately decayed into lighter elements, leading to a bright, radioactive "kilonova" astronomers could see some 85 million to 160 million light-years away from Earth. Light from the energetic breakdown of this material suggest that it led to the unimaginably valuable formation of about 50 Earth masses' worth of silver, 100 Earth masses of gold, and 500 Earth masses of platinum.
Researchers who've pored over the data since last year now think the collision also made 1-5 Earth masses of a very rare element called europium, according to a recent study in The Astrophysical Journal. (They also dialed back the gold-formation estimate to 3-13 Earth masses worth.)
The study could mean that neutron-star collisions are responsible for forging most of the europium and gold we find on Earth, not to mention other key elements.
What europium is and how its made
Europium is element number 63 on the Periodic Table, and it's a somewhat hard, silvery metal that reacts with oxygen and water — so it's never found in pure form. When it is pure, it's stored in inert gases (e.g. argon) to prevent it from oxidizing and tarnishing.
The element is used to make some red lasers, electronic parts, and the red phosphors of cathode-ray-style television sets. (One estimate suggests there's 0.5-1 gram of europium in every CRT screen.) Its ability to react to ultraviolet light also makes it an anti-counterfeit measure in euro paper currency.
Researchers suspected europium was formed by colliding neutron stars, but couldn't be sure how much until one was detected. Another explanation is that cataclysmic explosions of stars, called supernovas, form most europium and other elements heavier than nitrogen.
A bit of nuclear alchemy called the rapid process or r-process is what drives the creation of such heavy elements.
The r-process goes something like this: As neutron stars move toward each other, a tiny bit of their material gets shot into space at incredible speeds. Those neutrons are very hot and crowded, so they smash together while moving outward, forming giant atomic cores.
Because very big atoms are highly unstable, they almost immediately break apart and decay into smaller atoms — stuff like platinum, gold, silver, and europium.
Fortunately, we don't need a spaceship to find this stuff created by neutron stars — it's here on Earth. Countless smash-ups over the millennia spread around enough of these exotic metals that when our planet formed, they were baked right into its crust.
"The rate of these neutron star mergers in our galaxy is about one every 100,000 years. On human time scales, that's a long time," Duncan Brown, an astronomer at Syracuse University who's a member of the LIGO research collaboration, previously told Business Insider. "But on galactic time scales, when you're creating stars and solar systems, that's not that much time."
What's still uncertain is how much colliding neutron stars might contribute to europium. If LIGO finds more and more colliding neutron stars over the years, it's likely those events — not supernovas — are where the most valuable materials on the planet come from.