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Abstract:

A Fourier transform analysis of 2.5 million spectra in the Sloan Digital Sky Survey was carried out to detect periodic spectral modulations. Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range. The signals cannot be caused by instrumental or data analysis effects because they are present in only a very small fraction of stars within a narrow spectral range and because signal to noise ratio considerations predict that the signal should mostly be detected in the brightest objects, while this is not the case. We consider several possibilities, such as rotational transitions in molecules, rapid pulsations, Fourier transform of spectral lines and signals generated by Extraterrestrial Intelligence (ETI). They cannot be generated by molecules or rapid pulsations. It is highly unlikely that they come from the Fourier transform of spectral lines because too many strong lines located at nearly periodic frequencies are needed. Finally we consider the possibility, predicted in a previous published paper, that the signals are caused by light pulses generated by Extraterrestrial Intelligence to makes us aware of their existence. We find that the detected signals have exactly the shape of an ETI signal predicted in the previous publication and are therefore in agreement with this hypothesis. The fact that they are only found in a very small fraction of stars within a narrow spectral range centered near the spectral type of the sun is also in agreement with the ETI hypothesis. However, at this stage, this hypothesis needs to be confirmed with further work. Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.

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    I plotted the RA + declination of the stars detected and at my glance, they mirror the distribution of the SEGUE 2 dataset they’re based on. If these stars were all clustered right on top of each other that’d be compelling evidence of a local phenomena. The aliens would have to be really well-traveled for this to be ETI, so we’ll probably have another paper in a few years about a weird quirk of F2 to K1 spectral range stars.

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      Is it reasonable that this is 234 separate ETI contacts?

      On the face of it that makes it much less likely, but thinking more, 2 intelligent species in range seems a less likely number than 235?

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      Most of what I’m going to say is cribbed from the expert opinion on this. In particular, Jason Wright (involved in the Breakthough Listen initiative: if anyone would get excited about a bona-fide ET signal, it would be him) wrote a blog post in response to this describing how one should interpret claims of detections of extraterrestrial intelligence.

      I’m an astronomer, but not an expert on the observational techniques. However, given that SETI experts are less than enthusiastic about this, I’m erring on the side of the authors being far too generous in assigning likelihood to this being ETI and not, say, a bug in their data analysis or some systematic effect in a detector that they’re not accounting for correctly.

      Also, just on an aesthetic level, the plots in this paper are terrible. Presenting only black and white squiggly line plots with no error bars does not make for a persuasive story.