On March 7th, 2009, NASA launched its Kepler Space Telescope into space to discover Earth-like planets – also known as exoplanets, orbiting other star systems in our Milky Way galaxy.
Kepler’s sole instrument is a photometer, which is a device used to measure the light intensity of stars in a wide field of view.
The telescope was designed to scan the galaxy in a search for exoplanets in or near the habitable zones of their parent stars, and estimate how many of the billions of stars in the Milky Way have such planets by continually monitoring the brightness of the observed stars. Every 30 minutes, data collected from roughly 150,000 stars at time were sent back to Earth, which astronomers then use to analyze periodic dimming in brightness caused by exoplanets that “transit” their host star.
During its life cycle, Kepler observed more than 500,000 stars and detected over 2,600 planets before its retirement in 2018. However, the most interesting story told by Kepler’s data is not of the exoplanets, but of something much larger and even more mysterious.
A main sequence star designated KIC 8462852 – also known as the Tabby’s Star dubbed after astrophysicist Tabetha Boyajian who discovered it, located in the constellation Cygnus – approximately 1,470 light years from Earth, exhibited strange fluctuations in light unlike any other main sequence star observed by the Kepler Telescope.
The discovery was made by astronomers and citizen scientists from the Planet Hunters project back in September 2015 where the public were allowed to examine Kepler’s data. The main goal of the astronomers was to construct light curves; representations of the changes of a star’s brightness over time, and might even pick up something irregular that computer analysis had missed.
The Planet Hunters project later published an article describing this perplexing phenomenon and proposed several hypotheses to explain the star’s irregular change in brightness as measured by its light curve. None to date, however, fully explain all aspects of the curve.
Analysis of this irregular light curve suggests that an unusual transit occurred in front of the star. While a normal transit would only last a few hours, this particular transit however, lasted for an entire week. Furthermore, the star’s light curve was asymmetrical, seemingly indicating that the object in transit was not shaped like a planet.
In March 2011, Kepler’s data showed the brightness of the star dropping by 15% and lasted for a week. For reference, a planet the size of Jupiter would cause this star to dim by merely 1%. In February 2013 however, a massive 22% drop in brightness occurred around Tabby’s Star followed by a series of dips that lasted for over 100 days. Analysis of the trend of dimming in brightness suggests that there were many transits happening simultaneously during that period. But Scientists remained puzzled as whatever was transiting Tabby’s Star had to be 1000 times greater in area than Earth to block such amount of light for a long period of time.
At first, it was assumed it to be an error in the data. Astronomers combed through the information expecting to make corrections, but to their surprise, no errors were found.
In an attempt to explain this strange event, it was hypothesized that Tabby’s Star was young and surrounded by an uneven ring of dust or protoplanetary cloud, leftover from the nebular it formed from. However, there was no data present to suggest that the star is young, and if a protoplanetary cloud were present, there would be a visible glow observed around the star caused by the heated surrounding materials.
A second hypothesis suggested that the dimming in Tabby’s Star brightness could be caused by a massive swarm of comets whose solid mass and vapor trails would block the star light as they passed by it. However, astronomers also deemed this explanation to be unlikely as this swarm of comets have to be in high enough numbers in order to obscure the 22% drop in luminosity.
The most interesting and controversial hypothesis however, suggested that the changes in Tabby’s Star brightness could be signs of activity associated with intelligent extraterrestrial life when Tabetha took her findings to SETI in order to rule out the possibility that the star might be surrounded by an alien megalithic superstructure; a Dyson sphere or construct that harnesses its energy.
When news of Tabetha’s hypothesis was leaked to the press, they took the world by storm, with hundreds of articles on the subject and artists renditions of massive Dyson constructs proliferated the internet and news media. Scientists, however, remained sceptical about this explanation as this construct would have to be hundreds of times the size of the Earth to encompass the star; a technology beyond our imagination.
