If you haven’t heard about Tabby’s star, you’re probably wondering what the big deal is. The big deal is this. Over the last centuries astronomy has pretty much worked out how stars are born, age, and die. It depends on size mostly, but if astronomers know the mass of a star, they can work out how it will behave at just about every point of its life.
But Tabby’s star, also known as KIC8462852 or Boyajian’s star, is an oddity in a field where no oddities should exist. It dims up to 20% on an irregular schedule, which is something stars are not supposed to do. The theories for why have run the gamut.
Theory #1: A cloud of comets and dust surround the star, orbiting in irregular patterns and occluding the light in an unpredictable way. Say there were a billion comets orbiting the star, each with a different orbital period. Over time the percentage of comets between Tabby’s star and us would vary, and any pattern would be practically impossible to detect.
Problem with Theory #1: Over time a billion comets would diffuse through their orbital patterns in such a way that the star would always be dimmed to some degree. That is not the case.
Theory #2: Planet fragments. This one is similar theory #1, but instead of comets, the mass blocking the light is planetary remnants, the leftovers of some star system level smash up derby.
Problem with Theory #2: Nobody has been able to explain how a planetary system becomes a collection of planetary fragments.
Theory #3: This one is spectacular, the theory is that we might be watching the construction of an alien superstructure. If you’re familiar with the concept of a Dyson Sphere, an advanced civilization captures all the energy from its star via a thin shell of material around that star, and lives on the inside of the sphere once it’s complete. The surface area inside is equivalent to millions of Earths. This theory says that the shell isn’t complete yet, and light is being blocked by the parts that are built already.
Problem with Theory #3: The first problem is that we’ve found no credible evidence of alien life, let alone alien intelligent life. Radio and optical telescopes trained on Tabby’s star have found no evidence of radio or laser communication used to coordinate the building of such a massive engineering feat. So while theory 3 hasn’t been eliminated, it hasn’t a shred of evidence to support it.
Theory #4: Tabby’s star is eating a planet. The thought here is that Tabby’s star is consuming a gas giant. As the planet gets close to the star, the outer atmosphere and moons are stripped away, blocking light from the star and causing it to dim. Eventually the dust is cleared, either blown away by the solar wind or pulled into the star, and the star returns to normal.
Problem with Theory #4: The star has dimmed more than once. It is possible that the star is breaking apart the moons of any planet it consumed over time, but it’s not likely that the dimming would be so similar with each moon destroyed. Due to that similarity, this theory is unlikely.
Theory #5: The dimming is because of a gas giant several times larger than Jupiter with what may well be the most incredible ring system imaginable, as well as the Trojan asteroids associated with that gas giant. Trojan asteroids are dense asteroid fields that follow and precede a planet at the L4 and L5 Lagrangian points. Jupiter has them, so we know they’re possible and exist. A primer on Lagrange Points.
Problems with Theory #5: We haven’t had enough time to prove this one. If this theory is correct, there will be another dip in brightness in 2021. The dip in 2011 would have been the planet and the expansive rings passing in front of the planet. The dip in 2013 would have been the trailing asteroids at the L5 Lagrange point. The dip we’re seeing now could be from the planet passing behind the star, as the planet and those glorious rings would reflect a lot of light. So ironically the latest dip might not be the star at all, but the planet. In 2021, if the theory is correct, the L4 point asteroids will occlude the star, and we’ll finally have an answer that fits the observations. So the problem with Theory 5? Not enough time has passed to match the data to the theory.
There you have it. A summary of Tabby’s star and the behavior that has even the most respectable of scientists hoping they’ve finally discovered an advanced civilization. The favored theory by many at this time will be far more mundane, if you can consider a super-massive gas giant with rings that would make Saturn hide in shame mundane.