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September 8, 2018

Knowing just where to point your radio telescope to search for alien signals is one of the most vexing problems within the Search for Extraterrestrial Intelligence. The reason for this is two-fold. First, we have no idea where aliens might be. Astronomers can guess based on a star’s habitability and look for planets around those stars, and then point the radio telescope just to see, but that’s really about it. The other problem is that an advanced alien civilization could exist almost anywhere if they are space-faring. Star systems that might not be suitable for native life to arise, might be fully suitable for an advanced civilization to colonize.

This is compounded by the energy question within SETI. If you want to build a beacon; an intentionally conspicuous device designed to attract attention to a specific location; powerful enough for others to see, and have it run for long enough of a time, you need to expend massive amounts of energy. And that’s a problem. Why spend so much on the off chance that someone will see your beacon? It could well be that the reason we don’t see alien beacon signals everywhere is that no one broadcasts like that as a matter of practicality. That leads us to a question, are there situations where it would make sense for aliens to broadcast? Could there be a way to determine just when and where to look?

The answer is yes. Astronomical events themselves offer natural focal points for attention in the galaxy. Assuming that advanced alien civilizations study astronomy, it’s reasonable to say that any time anything happens in the galaxy, it gets noticed. One of the most visible events that can happen in a galaxy is a supernova. Whenever one happens, there’s a good chance that every telescope in the galaxy turns towards it, including our own.

“The only thing that scares me more than space aliens is the idea that there aren’t any space aliens. We can’t be the best that creation has to offer. I pray we’re not all there is. If so, we’re in big trouble.” – Ellen DeGeneres

This might make them a natural carrier or precursor for a communications signal. Any civilization that detects or even predicts a supernova might turn a transmitter the opposite direction of the supernova and blast off a contact signal knowing that as the supernova’s light propagates out, any civilization doing astronomy further from the supernova will be looking at it raising the chances that the alien signal will be detected in the process.

This is actually an old idea first proposed by Tong B. Tang, in his article in Journal of the British Interplanetary Society in July 1976. The article was named, Supernovae as time markers in interstellar communication. It ultimately means that recent supernova remnants might be natural places to look for signals in addition to the rare occurrence of a natural real-time supernova. But that’s not the only thing regarding supernovas and aliens that might be detectable at a distance. The fact is, supernovas are deadly if you’re close enough to them. But to a civilization only a little more advanced than we currently are, they need not be resigned to knowing their civilization was on borrowed time awaiting the explosion of a giant star located just a little too close. There is something they could do to protect themselves, and such a thing might just be visible at a distance.

It’s a blast shield and unlike most conceptions of an alien megastructure, this one is fairly easy to accomplish by moving around natural objects in your star system or Oort cloud; a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 50,000 to 200,000 AU (0.8 to 3.2 ly); to block most of the damaging radiation from the supernova or gamma-ray burst that would otherwise destroy you. In a 2016 paper, Long-Term Prospects: Mitigation of Supernova and Gamma-Ray Burst Threat to Intelligent Beings, by Milan M. Ćirković and Branislav Vukotić, they detail how to do this, and how we might do it if we need to.

But such an alien blast shield would need to be actively maintained and might be detectable by instruments like Kepler whenever it transits its star. You might more readily see such things in star systems that are located close to stars that are believed to be nearing a supernova or gamma-ray burst. 

I think this would be one of the more interesting ways to detect an alien civilization. Imagine a scenario where our first detection of an alien civilization is to see their supernova shield in a light curve. Perhaps others saw this too, and much of the galaxy worries about the safety of the supernova aliens. Perhaps they might anticipate that and the first transmission we receive from an alien civilization is a post-supernova message saying “we made it, here’s some data on what a supernova is like up close.”

Hope you like this post. Feel free to tell me which part needs to be modified or if I missed on something. Thanks for reading. Stay Healthy, Wealthy and Wise… Dreamers!