Aliens and Tabby’s Star: Everything You Need to Know

The updated story on the universe’s strangest star

The main goal of the Kepler mission, during which this star was discovered, was to find Earth-sized planets in our region of the luminous Milky Way. Image by NOVA.

It’s a simple concept: in our search for planets outside of the Solar System, we monitor the brightness of hundreds of thousands of faraway stars. The round, opaque bodies of planets will glide across the face of their host stars during orbit and will block a small percentage of light from reaching Earth. These transits are identified by computers and recorded as small dips in a brightness graph. Jupiter, king of planets, massive and regal from where it sits just beyond the asteroid belt, has more than twice the mass of all the other planets in our system combined. It’s crowned by a set of faint, glowing rings first discovered in the 1970’s by Voyager 1. They’re composed of one inner main ring and a wider, wispy Gossamer ring that stretches thousands of miles into the fabric of space around the gas giant. But even a planet as lofty and hearty as Jupiter would only cause a 1% drop as it passed in front of its host star. Earth, beautiful but quite dainty by comparison, leaves very little in the way of a mark on the graphs at all.

These transits are the main way we find exotic worlds around stars we might someday hope to visit. But in spring of 2009, in the midst of NASA’s Kepler mission, it wasn’t another planet we found sauntering around star KIC 8462852 (Tabby’s star or Boyajian’s star). In fact, we didn’t know what could possibly be causing the strange signals coming from that direction. Over the years, the behavior was unpredictable and full of mysteries which haven’t been completely resolved to this day. Answers to the puzzle that is Tabby’s star ranged from natural phenomenon to tenuous but exciting proposals of alien technology. It was — and remains — the first observation of its kind.

The signal was only somewhat confusing at first. The star itself is comfortably situated over 1,300 lightyears away and is 50% bigger than the sun. It’s a stable star, burning now for hundreds of millions of years and giving off four times more light. Yet a decade ago, a giant object crossed in front of the star and left an asymmetrical dip in the graph. As big as Jupiter but not round in shape, the object’s transit lasted almost a week where most other transits had a lifespan of only a few hours. After 2 years of relative quiet, the next dip in the graph obscures the star’s brightness by 15%. The light is blocked gradually over the course of about a week, with the transit dissipating as quickly as it came and then again leaving us in an ominous silence. The proceeding dimming comes once more in a balmy spring 2 years later; the dips last for over 80 days, varying in shape and duration, overall diminishing the star’s brightness by more than 20%. It was clear that whatever the object was, it would no longer classify as a planet since Jupiter is about as big as a planet can get before delving off into brown dwarfs and stars. There was also no infrared radiation, meaning that the object was cold, and likely not orbiting close to the star.

The data couldn’t be right. And yet scientists confirmed that there was nothing wrong with the observations.

Images from NASA show the star in infrared and ultraviolet.

Every natural explanation for what was happening continued to come up short. While stars are often born from clouds of interstellar material that collapse into hot, dense cores, Tabby’s star isn’t young and the material would have given off a glow as it was heated by the star during orbit. But there was no glow, meaning that this initial cloud (or possible material from colliding planets) couldn’t be the cause. Comets passing in our line of sight was a slightly more reasonable idea but it would have taken as many as tens of thousands of comets to produce our observations. The data wasn’t consistent enough to be a planet and a lack of spectral lines suggested no material was collecting or being ejected from the star itself.

For a while speculation led to a band of rings. A small planet mounted by some wavering, expansive rings and orbiting close to the star could block out a substantial amount of light. The variation in dimming could be a product of gravity tilting the rings in different directions, consequently blocking more or less light from the star. But here again we ran into problems. Not only would the ring system have to be enormous — three times the diameter of Saturn’s — but it would be much more periodic as its planet orbited the star. The tilting of the rings would also be consistent (in May of 2017 dimming was only 2% compared to past data of 15% and 22%) and the same gravity which caused them to dip would pull them apart in a matter of a century. That is, they shouldn’t be around for us to observe them.

Given the circumstances, it’s easy to see why Tabby’s star has been named “the strangest star in the universe”. As all the natural causes were proposed and then curtailed, researchers began to wonder if an artificial system was to blame.

The artist’s rendition above shows a Dyson Sphere harvesting energy. To dim Tabby’s star according to our observations, this alien structure would have to be at least half the size of the star itself. Researchers from Princeton University even searched for signatures of lasers coming from Tabby’s star, proposing that a civilization may try to communicate with laser technology. Image by NOVA.

The idea of alien megastructures built around stars has been popular since the 1960’s. An advanced civilization will run out of energy to use on its home planet and it will then build energy-harvesting structures like a Dyson Sphere around its host star. A lack of infrared signature could mean that the heat energy was being redirected elsewhere; for example, to an engineering project we couldn’t even begin to fathom. It was even more encouraging that the material causing the dips seemed to be situated just far enough away from the star to be in the habitable zone — the perfect position for life to develop. The SETI Institute (Search for Extraterrestrial Intelligence) became involved and trained their Allen Telescope Array on the star in May of 2017. The goal was to monitor for artificial radio transmissions.

It was data from this time period (May to August of 2017) that began to unravel the mystery of Tabby’s star. Not all wavelengths of light are dimmed equally. More blue light was blocked than red light, meaning that the object could not have been opaque the way it would be in the case of a planet, a moon, or an alien structure. The uneven scattering or blocking of different wavelengths is exactly what’s seen when circumstellar dust gets in the way of light. Circumstellar dust is 1,000 times smaller than a grain of sand but larger still than interstellar dust. Pressure from a star’s light can shift the dust, causing some of it to move out of orbit. This means the dust around Tabby’s star, though recently created, isn’t likely to have a long lifespan.

While the mystery of what’s causing the star’s flickering may be solved, there are still the questions of where the dust came from, what it’s made of, and why it happens to be gathered where it is. Circumstellar dust is most commonly seen around younger stars, not those the age of Tabby’s star.

As seen here, blue light causes greater dips than red light, meaning that more of it is obstructed during travel. This applies to both the short-term dips and the century long dimming of the star. The conclusion came from studying over 19,000 images taken over the course of 3 years. Image by NOVA.

And it’s not just light that’s being blocked from our telescopes. Tabby’s star has been known since the 1890’s and the stellar object has decreased in brightness by 16% over the last century. A different kind of dust, bulkier and more resistant to pressure, is thought to be the cause. Theories regarding the origin of this dust range from swarms of comets and asteroids to the consumption of a Uranus-sized planet. Bust dust like that of a comet is a fleeting material and it would disperse within months, meaning that if they’re what’s causing the star to dim down, they must be supplying it in continuous waves. Some other unknown, external factor of Tabby’s star could be behind the diminishing brightness.

More signals are expected in June of this year, though scientists wait in anticipation for the James Webb Space Telescope that’ll be up and running by the year 2020. Using the telescope, researchers should be able to determine what exactly the dust is made of, bringing us one step closer to understanding this compelling, famous point of light.

While it was machines which were trusted to analyze the data from the Kepler mission, ultimately it was a group of over 300,000 people who brought Tabby’s star to scientists’ attention. The human brain has evolved to be, in many cases, even better at pattern recognition than a computer. And while we may use instruments to uncover the cosmos around us, it’s important that we remain involved ourselves; ever curious, peering at the numbers and keeping an eye out for the details which try to escape us. Details, that is, like the delicate glossy rings of our Solar System’s largest planet.