What Does S.E.T.I Actually Look For?
What does SETI look for?
The other week we saw an interesting question on reddit “What does SETI (The Search for extraterrestrial intelligence) look for. It gathered a lot of interesting answers, however it was covered in extraordinary depth by a Radio astronomer who gave a rundown of the main things that they are keeping theirs ears open for!
In short we’re looking for transient radio signals (ie signals that turn on and off instead of being constantly there).
Fast Radio Bursts (FRBs) have been in the spotlight recently making numerous appearing on various news stations. FRBs are high-energy astrophysical phenomena manifested as a huge transient radio pulse lasting only a few milliseconds.
Discovered in 2001 the The Lorimer Burst lasted less than 5 milliseconds in duration and was located near the Small Magellanic Cloud.
Since then we have now recorded about two dozen, through a collaborative effort of radio telescopes around the world. Out of the 19 detected so far only one has ever repeated itself! Due to this isolated nature, trying to identify the sources or causes of these phenomena, is extremely challenging meaning the nature of them still remains unknown.
Through observations of FRBs it is generally accepted that the emission region is estimated to be no larger than a few hundred kilometers across and must be extremely bright if the origin of the burst’s come from cosmological distances.
One of the leading hypothesis is a collision event between two very dense objects such as, collapsing black holes or neutron stars. It has also been suggested that there may be a connection between FRBs and gamma-ray bursts – the only other one-off transient events that we are currently aware of.
Back in 2002 a group of 5 radio bursts of equal brightness, each lasting about 10 minutes, and occurring every 77 minutes were detected. This famous string of bursts were named The Great Galactic Burper. Originating from near the galactic center we have detected other burst from that area but it hasn’t provided any information on the source of it . The leading hypotheses include; a nulling pulsar, a pair of orbiting neutron stars or a pulsar precessing with a period of 77 minutes.
Then we probably the most famous radio transient signal. The “Wow!” signal. in the 1970s, a SETI survey received a very bright, narrow-band signal in the part of the spectrum where many radio astronomers have speculated radio signals from extraterrestrial life may be located. It was registered for about 72 seconds as that patch of sky was overhead, and nothing like it has ever been seen again. The scientific community is still split around this as as some think it may have been man made however many consider it to be from a natural source such as the possible release of hydrogen gas from comets passing in front of the telescope.
Currently humanity only observes a very small fraction of the sky, so when a transient signal is transmitted on part of the sky that you’re not looking at, we will miss it completely making it appear like it never existed. However with the continual, and rapid advance in technology and techniques of low-frequency radio astronomy, this small handful of signals detected so far may be the first of many of this nature to be discovered.
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