What is causing the puzzling light-curve dips of the so-called "alien mega-structure" star, Boyajian’s Star? A recent discovery examines a variety of promising explanations to define which ones are the most acceptable. Earlier this year, astronomer Tabetha Boyajian stated on the mysterious light curve of the star KIC 8462852. This star, now named "Tabby’s Star" or "Boyajian’s Star", shows mysterious dips on day-long periods that are too big to be explained by planet journeys or similar phenomena.
In this artist’s drawing, a star’s light is obstructed by orbiting comets. A group of comets is just one
of the many descriptions that have been suggested for Boyajian’s unusual light-curve dips.[NASA/JPL-Caltech]
Furthermore to these short dips in light, recent observations have also shown that the star has faded by approximately 20 percent over the past hundred years. What could be affecting both the short-term dips in the star’s light and the long-lasting dimming over a century?
Could the dimming be affected by an ‘alien megastructure constructed by an extraterrestrial civilization? The authors find that a sphere-shaped structure is very doubtful. [Danielle Futselaar/SETI International]
Boyajian’s Star was curved into the media highlight when astronomer Jason Wright (Pennsylvania State University and University of California, Berkeley) suggested that its mysterious light-curve could potentially be described by a nearby mega-structure manufactured by an extraterrestrial civilization.
Now Wright is back with co-author Steinn Sigurd̵sson (Pennsylvania State University). In a new discovery, Wright and Sigurd̵sson examine an extensive list of reasons for the mysterious apparent behavior of Boyajian’s Star, based on our newest knowledge about this strange object. Here are just a small number of possible causes of Boyajian’s Star’s dimming, as well as the authors’ calculation of their plausibility. Check out Wright’s own summary of the article here!
- Pulsations, polar spots, and extra stellar variability: unlikely
The authors show that the change of timescales detected for dimming events makes situations linking stellar variations unlikely.
- Circum-stellar material: unlikely
Material revolving the star (like comets) would describe some of the light-curve dips, but it cannot explain the long-term dimming detected.
- Post-merger arrival to normal: unclear
Maybe Boyajian’s Star just merged with a brown dwarf or another star? Now it could be steadily dimming as it returns to its usual brightness, and rearranging of the star’s material could cause the short-term dips. Though this situation is possible, the timescales for the brightness variation are shorter than we would suppose.
- Artificial structures: unclear
Spherical groups of structures would interrupt the star’s light and re-radiate it in infrared. Since long-wavelength explanations have found no sign of such radiation, the author says spherical geometries to be doubtful. Other structure geometries cannot so far be ruled out, though.
- Small-scale interstellar medium (ISM) structure: likely
Small-scale density differences in the ISM between us and Boyajian’s Star could affect the dimming we observe, but the fact that nearby stars do not show related dimming sets tight limits on the size of such ISM clusters.
Spectral energy distribution of Boyajian’s Star. The upper-limit arrows on the righthand side show that big clouds of mega-structures are doubtful because we would discover their heat they re-radiate the star’s light in infrared. [Wright et al. 2016]
Of the promising locations for the source of the dimming, Wright and Sigurd̵sson deem the stellar space between us and Boyajian’s Star to be the most likely culprit. They found numerous future lines of research that could help us further remove possibilities, however, with a study of the ISM toward Boyajian’s Star, a hunt for comparable variations in stars near in the sky to Boyajian’s Star, and infrared observation of the star with JWST to hunt for heat signs.
Read the authors’ original article.