Best Place for an Alien Civilization

This story popped up yesterday, and I can imagine it will go far, since it talks about life in the universe.  I get it, it’s what people are interested in, and at least this story is focused on the science of why this is the best place to look for intelligent civilizations, instead of “Oh hey there’s a strange ring of material around a star, must be an alien superstructure.”  But I digress.

So where is the best place to look for life in the universe? The answer is in a Globular Cluster.

Globular star clusters like this one, 47 Tucanae, might be excellent places to search for interstellar civilizations. Their crowded nature means intelligent life at our stage of technological advancement could send probes to the nearest stars. Credit: NASA, ESA, and the Hubble Heritage Team

A globular cluster is one of the oldest structures in the universe.  Consisting of ancient stars, most of them formed about 10 Billion years ago, and contain millions of stars in a densely packed space only 100 light years across.  The Milky Way is host to about 150 of these clusters, but some larger galaxies can have thousands.

So why are they such good places for life to develop?

Because they are very old, they tend to be lacking in the heavy elements that life needs, like Iron and Silicon, since their stars haven’t died and enriched the surrounding interstellar medium.  This should make them very unlikely to host planets and subsequently life.  In fact, only one planet has ever been discovered within a globular cluster.

But this could be a premature assessment.  When looking at exoplanets in general, there is definitely a preference for Jupiter size planets developing in metal-rich environments, but so far there is no preferential environment for Earth-like exoplanets.

The other cause for concern in a globular cluster is the fact that stars are packed so close together, any gravitational interactions from a star that passes by could send planets flying out into the cold of interstellar space.  And yes space is very cold, even in the densely packed globular clusters.

But here’s the thing, the more massive stars in a globular cluster would have died out long ago since they would burn through their fuel more quickly, and so most stars are smaller and redder, giving them less ‘muscle’ when interacting with other stars gravitationally.  They would also have a habitable zone (range of distances from a star where water could be liquid) closer to their star, meaning any habitable planets would orbit closer and be much harder to perturb.  Maybe globular clusters are good places for life.

If life formed in a globular cluster, the nearest star would be about 20 times closer than the nearest star to the Sun.  This means that any advanced civilization could master interstellar travel and communication much more easily than we can.  If this is possible, they could get to higher levels of technology in a shorter period of time.   Maybe we have to start looking for signals from intelligent life in a globular cluster.  Maybe the first step is trying to find planets and showing that they are plentiful in such an environment.  Or maybe we will never know.


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