Free Astronomy Magazine September-October 2024

9 SEPTEMBER-OCTOBER 2024 ASTRO PUBLISHING H ydrogen-alpha (H-alpha, H ! ) has a wavelength of 656.28 nm and appears red. It corresponds to the transition of an electron from the state with principal quantum num- ber n = 3 to the state with n = 2 in the hydrogen atom. A photon with a wavelength of 656.28 nm is emitted, producing a spectral line with the longest wavelength in the Balmer series. If a Dyson sphere candidate star shows this type of emission, it is very likely that it is a young star sur- rounded by the remnant of the disk of gas and dust from which it was born. In this case, the excess infrared emission is not attributable to an alien megastructure. I mages of the Fomalhaut ring in diffuse visible light (HST, panel a, from Kalas et al. 2013), in the far infrared at 70 µm (Herschel, panel b, from Acke et al. 2012,) and in thermal emission at 1.3 mm (ALMA, panel c, from MacGregor et al. 2017). The scale bars represent 50 astronomical units. The seven candidates found by Suazo's team could be systems similar to this one, which are particularly bright in the infrared. Further spectroscopic investigations will be needed to confirm this. dynamic properties compatible with the presence of alien megastruc- tures. To harmonize and cross-refer- ence the information contained in the different databases, the team had to develop a complex procedure with various filters through which the data from about five million sources passed. This first phase al- lowed them to identify a series of potential candidates that show an excess of in- frared radiation not ap- parently attributable to any natural source. A second screening mainly concerned the detection of strong H-alpha emis- sion lines and variability in the visible spectra of the potential candidates. The H-alpha emission line was selected as a way to remove a candidate be- cause it is a significant sig- nal in the residual pro- tostellar disks of mostly young stars, those un- likely to host a species old or ad- vanced enough to build a megas- tructure. The variability in visible light for a candidate was used as a filter for the same reason, as such behavior is expected from very young stellar objects, whereas only very accentuated and possibly regu- lar light curves would be compatible with orbiting megastructures. After subjecting the approximately five million sources to these various filters, the team led by Suazo was left with only 368 targets. Of these, however, 328 were not resolvable as single objects but rather appeared as a mixture of sources. Another 29 showed irregular variability, and a further four turned out to be nebu- lar. At the end of the long selection