Would Alien Civilizations Be Rich? Depends How Close They Are to Colliding Neutron Stars

An artist's depiction of two neutron stars colliding. NASA/AEI/ZIB/M. Koppitz and L. Rezzolla

Last summer, scientists spotted colliding super-dense neutron stars for the first time ever. One of the most exciting consequences of that discovery was confirming that such mergers create many of the heavy metal elements we use here on Earth—elements like gold, uranium and platinum.

That realization could have far-reaching implications. Just as those elements have shaped our own civilizations, they may shape the civilizations of any extraterrestrial lifeforms in the universe as well, Harvard University astronomer Avi Loeb suggests in a new essay.

"These mergers are rare," Loeb told Newsweek. "It occurred to me that being close or far from such a merger would have dramatic implications for the extraterrestrial civilization."

Here's what happened on August 17: Gravitational wave detectors picked up tiny ripples in the fabric of space. The ripples matched a burst of light astronomers quickly spotted in the same area of the sky. That explosion, called a kilonova, confirmed a long-standing theory: that the heaviest natural elements are created during these celestial fireworks.

Neutron stars, as the name suggests, are packed with neutrons, a type of subatomic particle, formed by gravity forcing other types of subatomic particles together. But when two neutron stars collide, a fraction of all those neutrons are flung out into space.

There, existing atoms can snatch up these loose neutrons, creating large, unstable clumps that decay in a process called rapid neutron capture.

This process is what originally formed some or all of the heaviest half of natural elements—familiar faces like gold and silver, uranium and plutonium, but also less famous elements like molybdenum, xenon and rubidium.

Because we've only spotted one such collision so far, there are still lots of questions about the math behind the phenomenon. How often do neutron stars collide? What proportion of their mass is turned into these heavy elements? Wow do those rates affect the elements on a nearby planet?

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But several of these elements play key roles in our own civilization, so it's only logical that having more or less of them may make civilization look different on different planets, Loeb said. Molybdenum in very small quantities is crucial to life in any form, intelligent or not. Gold underlaid economic systems for millennia, so its abundance could shape similar systems on other planets. Uranium and plutonium could affect a civilization's nuclear weapons or energy supply.

And the bounty of elements bestowed on some distant culture could help us find them. Our current approaches to finding extraterrestrial intelligence rely on spotting signatures of communications technology. Elements used in those technologies, like rubidium, could determine whether we can spot our neighbors.

"The location of the planet in its host galaxy matters for the quality of galactic life," Loeb said. "We tend to think of our conditions as sort of typical, but that's not always the case."