Oct 13 2022

Another Possible Technosignature Falls

Published by under Astronomy
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One day it may turn out that a potential sign of alien technology (technosignature) turns out to be just that. That is the best hope of finding evidence for life outside our solar system in my lifetime. But that day has not yet arrived, and another potential candidate (although this one was pretty weak) has found a natural explanation.

Of course no one knows, because we only have one example of life and a technological civilization, but if I had to guess I would say the universe is teeming with life. We’ve now confirmed what scientists long suspected, that our solar system is not unique or rare. Most stars have lots of planets around them, including rocky worlds within their habitable zone. Also, life seems to have arisen very quickly on Earth, as soon as the conditions were compatible with organic life. We may also find that life once existed on Mars, and may still exist in one or more ocean world, like Europa. Discovering even microbial life that originated independently from life on Earth would be huge – it would give us a second data point. It would confirm that life is likely everywhere it can form.

The probability, and therefore density, of technological civilizations is another matter entirely. It took the Earth about 4 billion years of tinkering with life before a technological species arose, and it happened (so far) only once. We have also not been around for very long, and there are many plausible scenarios by which our geological presence on this planet may be relatively brief. The famous Drake Equation mathematically frames the question, but that does not help us fill in all the variables. We simply don’t know. It is possible we are the only current technological species in the galaxy, or there may be hundreds, or even thousands. It also possible that ancient technological species, now long dead, have left behind evidence of their existence – their radio signals still streaming through space, or massive megastructures that reengineered entire stellar systems.

The reason I think finding such evidence is our best hope of detecting non-Sol life is that astronomers can search vast parts of the universe, and frequently detect even extremely rare situations and events. We have increasingly powerful and sophisticated instruments, like the James Webb telescope, that will help us find such things, if they are out there. Webb recently helped astronomers resolve an anomalous finding, although this one has a natural explanation (as all anomalies have gone before it, so far).

The star is WR140, a binary star about 5,000 light years from Earth. Prior images of the system found it was surrounded by concentric regular rings. Structures that have mathematical precision tend to make us think of artificial construction. Was this some kind of megastructure surrounding WR140? This idea was really just popular speculation, and never a serious proposal. The concentric rings extend out for 10 trillion km, a little over a light year. Also, nature provides abundant examples of naturally occurring mathematical sequences, from the shape of a pinecone, to the precisely regular rotation of pulsars.

The Webb telescope was pressed into service, taking stunningly detailed pictures of WR140. Webb confirmed that WR140 is a binary system, and that these concentric rings are just dust. Why are they spaced our in regular rings? This represents another common phenomenon in astronomy – when potential technosignatures are found to be natural in origin, we tend to learn some really cool astronomy.

The “WR” in the system’s name stands for Wolf-Rayet, a type of star that is very large and very active. WR140 has a 30 solar mass Wolf-Rayet star, and another O-type star, about 10 solar masses – although it probably started its life at about 30 solar masses. The two stars orbit each other every 7.93 year. They are also what is referred to as a “wind-binary” – their solar winds interact with each other as they orbit very close. The Wolf-Rayet star is also pumping our carbon-rich and mineral-rich dust, and the orbit of the two stars is essentially blasting that dust out in a 7.93 year cycle as their solar winds interact. Their orbit is eccentric, and the power of that blast is greatest as they are moving toward and away from each other.

The net effect is the concentric ripples of enriched dust. The rings are irregular because of the variable effects at different stages of the orbit. Also, Webb is not imaging the system directly face on, so it’s partly an optical illusion.

Another interesting aspect of this phenomenon is that wind-binary star systems like WR140 may be responsible for a significant amount of enrichment of the interstellar medium, and therefore seeding next generation star formations that are surrounded by planets enriched with carbon and minerals.

I’m not disappointed at all by this one, because this was never a serious contender as a technosignature, and the actual science is extremely cool. The one that most had my hopes up so far was Tabby’s star, with unprecedented dips in the light curve from the star. Hopes of a “Dyson swarm” type megastructure faded fast, however, when it turned out the system was not glowing in the infrared, like a megastructure should, and it was confirmed that the dip is due to a large cloud of dust. Other claims never really impressed me, including Oumuamua. Such claims are mostly an argument from ignorance, but of course such a discovery is likely to start that way – we don’t know what this is. But at this point we need something more interesting than that, we need some positive evidence for something potentially technological. I hope to see what that may look like one day.

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