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'Ghost Signals' of Extraterrestrial Civilizations Haunt the Milky Way --Suggests the New Drake Equation (WATCH Video)

Today's Top Space Headline --"For Alien Civilizations, Proximity to Neutron-Star Mergers Could Determine Survival"



Imagine an extraterrestrial (E.T.) civilization on the surface of a planet that is deficient in uranium relative to Earth. Such a civilization will be less likely to develop nuclear weapons and to annihilate itself through a nuclear war. A lower abundance of gold would make this element more precious and have a major impact on the E.T. economy. Hence, both the economy and longevity of an E.T. civilization will depend in part on how far it is from its nearest neutron star merger.

Astronomers have recently determined that rare elements such as gold and uranium are produced as a result of rapid capture of free neutrons during the merger of two neutron stars, writes Harvard's Abraham Loeb, Chair of the Department of Astronomy and Founding Director of Harvard's Black Hole Initiative in today's Scientific American . Neutron stars are the densest stars known, having the size of a city (12 kilometers) and up to twice the mass of the sun, with the density of an atomic nucleus. A teaspoon of neutron star material weighs a trillion kilograms, as much as a tall mountain on Earth.


Last summer the LIGO experiment detected ripples in spacetime (so-called gravitational waves) that were produced by the merger of two neutron stars in a distant galaxy. The light emitted after the merger provided evidence that a small fraction of the neutron-rich matter was ejected into space and transformed to elements such as gold or uranium. The expected rate of such mergers can account for the average abundance of these elements in galaxies.

But neutron star collisions are extremely rare and so the abundance of gold or uranium is expected to vary considerably in space and time within any given galaxy, as long as subsequent mixing processes are incomplete. Indeed, spectroscopic studies of galactic stars reveal a large spread in their abundance of europium, a related heavy element. Under these circumstances, one cannot help but wonder how the history of extragalactic civilizations would be shaped by their distance from the nearest neutron star merger.


There is no doubt that the cosmic neighborhood matters in shaping the life of civilizations. For example, Proxima b is the planet orbiting the nearest star to the Sun, Proxima Centauri. Even though the planet is merely 4.2 light years away from us, any form of life on Proxima b must experience a very different life than ours. Since the host star is faint (having 12% of the mass and 0.2% of the luminosity of the sun), the habitable zone around it—where Proxima b resides— is 20 times closer than the Earth is from the sun.

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