In a blow to ET-hunting hopefuls, a large team of astronomers using multi-layer analyses of high-resolution data gathered by a specialised planet-finding telescope at California’s Lick Observatory have failed to find any evidence that extraterrestrials are mucking about with lasers or an alien megastructure near a star some 1468 light-years from Earth.
The findings, by researchers led by David Lipman of the University of California, Berkeley, represent arguably the end of the last faint hope that evidence of an alien-built megastructure had been found.
The evidence – most recently interpreted in a tentatively ET-friendly way by Pennsylvania State University researchers Jason Wright and Steinn Sigurdsson in 2016 – concerns Boyajian’s Star, located in the Cygnus constellation.
The star, named after the lead author of the paper that first described it, Tabetha Boyajian of Louisiana State University, US, is widely regarded as the oddest thing thus far found in the universe. This is primarily because it has been observed to undergo seemingly random and rapid dips in its luminosity, ranging from small to huge – in one instance, in 2013, losing 22% of its brightness.
The lack of any determinable pattern, or periodicity, to these fluctuations has exercised the imaginations and datasets of astronomers for many years, with several explanations being put forward.
Most of these do not invoke the influence of alien civilisations. They have included a collection of small planets moving around in front of the star (relative to an Earth-based observation point), a swarm of comets, or a huge cloud of interstellar dust.
Other astronomers and astrobiologists, including Wright, have noted that the evidence for Boyajian’s Star does not preclude the existence of some type of alien megastructure. The most common visualisation of such a structure is what’s known as a Dyson Sphere – a hypothetical structure conceived in the 1960s by physicist Freeman Dyson. Such spheres would comprise a large number of solar collectors arranged in a ring, or a globe, around a star, serving as energy-collectors to power some form of alien tech.
In a 2015 paper, Wright and colleagues noted that not only were the available data on Boyajian’s Star not incompatible with the idea of a partially light-obscuring megastructure, information collection protocols were set up in a way that such a structure would not be directly detected. They suggested 10 ways in which telltale signs of an ET power station might be found in future surveys.
One of those was to check for laser signatures, on the not unreasonable grounds that any structure large enough to encase a star – Boyajian is almost one-and-a-half times the mass of the sun – would have an internal communication system, for which lasers would represent a good candidate medium.
In the latest research, Lipman and colleagues decided to test the idea. They analysed 177 high-resolution spectra from the star, gathered by the Lick Observatory’s Automated Planet Finder telescope as part of the Breakthrough Listen Project.
They estimated that the data was so detailed that lasers with power greater than 24 megawatts should show up. To hunt for them, the researchers developed an algorithm to perform a pixel-by-pixel analysis of each spectrum in order to identify “spatially unresolved emission lines that meet the criteria for an artificial laser signal”.
The good news is that they found several. The bad news is that a secondary multi-step analysis designed to pick up false positives discounted them all.
“The top candidates from the analysis can all be explained as either cosmic ray hits, stellar emission lines or atmospheric air glow emission lines,” they conclude.
Hope, however, may yet spring eternal. Lipman and colleagues also note that current technology cannot pick up laser emissions less powerful than 24 megawatts, and that lasers used for communication would, by definition, be used only intermittently – so it’s still possible that they missed something.
Related reading: The tech we’re going to need to detect ET
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