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Gamma-Ray SETI

April 10, 2012 | Comments: 0 | Views: 183

SETI (Search for ExtraTerrestrial Intelligence) scientists search for ET's intelligent messages in the radio spectrum; and also in the visible region of the electromagnetic spectrum. Should they, despite the inherent difficulties, take the opportunity to analyse gamma-ray bursts for a signal in the gamma radiation noise? If they in fact they already have been examined for a signal I'm unaware of it or any such analysis and conclusions. It's those unexpected and short-lived aspects that make gamma-ray SETI difficult in the extreme. It's like sometime in the next 24 hours, on just one radio station, in some unspecified part of the world, lasting for only ten seconds, you will hear a voice. Good luck picking it up.

Gamma-ray bursts were discovered accidentally by the Vela series of satellites. The Vela satellites were sent up by the Americans to keep tabs on those naughty commies and to make sure they didn't violate the Nuclear Test Ban Treaty. The Vela satellites indeed picked up one of the telltale signatures of atmospheric nuclear explosions (gamma-rays), except they weren't coming from Terra Firma or within our atmosphere, but somewhere out there - way, way, way out there. Though first detected in 1967, the anomalous nitty-gritty details weren't made public until about six years later - well these after all were top secret military spy-in-the-sky satellites.

Anyway, it was quickly realized that these cosmic gamma-ray bursts were coming from really, really far away. They weren't sourced locally; they weren't sourced at interplanetary distances, or even at interstellar distances. They were happening in galaxies far, far away, so far, far away that they happened a long, long time ago too (since it takes electromagnetic radiation, of which gamma-rays are a part thereof, finite times to cross finite distances). To cross such vast distances with such energy intensities suggested that gamma-ray bursts were not akin to a galaxy what a firecracker is to Planet Earth. Rather, it was more a galactic case of, well a terrestrial super-duper nuclear explosion on Planet Earth.

Now gamma-rays are very high energy electromagnetic photons, more energetic than ultraviolet and X-rays. Even before the detection of those intergalactic gamma-ray bursts, we knew about gamma-rays since they are a natural product of electron - positron annihilation and of some radioactive decay processes.

So much for some background on gamma-rays and astronomical bursts of gamma radiation, how might that apply to SETI? Let's assume that there is at least one highly advanced technological extraterrestrial civilization somewhere out there, who wishes to draw attention to themselves via a signal of some sort (which is not quite the same thing as actual one-on-one communication). That desire might be akin to a more relevant terrestrial analogy like an anonymous show-off graffiti artist - "here I am; I exist". How would, or at least could, our ET do it?

Now what's the biggest cosmic bang advertisement for your buck you can get? My understanding would be matter-antimatter annihilation. If an electron meets a positron, you get a gamma-ray. So, I wonder whether the rather anomalous and unpredictable gamma-ray bursts that are somewhat common, but not too common in the cosmos, might, or at least some of them might, be artificially created by that highly technological extraterrestrial civilization or perhaps, if plural, those extraterrestrial civilizations. An alien 'message' (as it were) or signal, in plain sight.

Here's another possible scenario. Say once upon a time, billions of years ago, you had various, even numerous, high-tech extraterrestrial civilizations in various galaxies. In the classification scale of ET civilizations they would fall somewhere between a Type II (mastery of the energy output of a stellar object) and a Type III civilization (mastery over the energy resources of an entire galaxy). They shared information ('communication' in real time being out of the question due to the intergalactic distances involved) via radio waves, laser beams, etc. It's efficient to send an electromagnetic packet of info in a tightly compressed, and short-lived, burst. In-person travel to and on-site visitations, possible in interplanetary and interstellar scenarios, are impossible when it comes to intergalactic scenarios. The distances are just too vast.

Now, Cosmology 101, the expanding universe, tells us that most galaxies are moving away from most other galaxies. To keep intergalactic 'communications' or data sharing viable over the long term, you need to shout louder as time goes by; as your neighbouring or nearby galaxies gets farther and farther away from you. Gamma-ray bursts are 'louder' than most other energetic phenomena in the Universe. The basic data sending principle is the same. If you can use light waves or radio waves, etc. to send a message, why not a gamma-ray?

The drawback is that this is really high-energy expenditure. But, if you are a Type II or Type III civilization, 'burning' this amount of energy is akin to a billionaire lighting a match.

Now the odds are very high that in all probability, gamma-ray bursts are a totally natural phenomenon, albeit still a very mysterious one. But, you never know. I think it premature to rule out ET, at least until such time as we have a better grounding in the theory behind them and/or do a detailed analysis of a typical gamma-ray burst happening looking for some signal in the cosmic noise but not finding any.

Science librarian; retired.

Source: EzineArticles
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