Tabby’s Star, officially KIC 8462852, is a celestial object approximately 1,470 light-years from Earth in the constellation Cygnus. This F-type main-sequence star, slightly larger and hotter than our Sun, gained attention after astronomer Tabetha Boyajian, its namesake, led the 2015 paper announcing its unusual behavior.
The Star’s Unpredictable Dimming
Tabby’s Star captured astronomers’ attention due to its highly unusual and irregular dimming events, observed by NASA’s Kepler space telescope. Kepler, designed to detect exoplanets by monitoring stellar brightness, recorded unprecedented dips in KIC 8462852’s light. These dimming episodes were unlike anything typically seen for a main-sequence star, where a planet’s transit causes a small, predictable dip.
The star’s brightness decreased by varying amounts, with some events showing drops as significant as 15% and even up to 22%. These fluctuations were not periodic, and their duration varied from a few days to weeks. Such erratic and substantial dimming puzzled scientists, suggesting a large amount of material intermittently blocked the star’s light, far more than a typical planet could account for.
Beyond these dramatic, short-term dips, Kepler data also revealed a more gradual, long-term dimming trend. The star faded by about 0.34% per year over the initial 1100 days of Kepler observations, followed by a more rapid drop of 2.5% in just 200 days. This sustained fading made it a unique object of study.
Exploring the Explanations
The perplexing behavior of Tabby’s Star prompted scientists to propose various hypotheses, ranging from conventional astronomical phenomena to more speculative ideas. One early and widely discussed natural explanation involved a swarm of comets. This theory suggested a large family of comets or their fragmented debris, possibly disturbed by a nearby object’s gravity, could pass in front of the star, creating irregular and significant obscurations of light. However, explaining century-long dimming would require an implausible number of comets, estimated in the hundreds of thousands.
Another set of explanations focused on planetary debris or dust clouds within the star’s system. The disintegration of a planet or a massive collision between planetary bodies could create extensive dust and debris fields, which would then block the star’s light as they orbit. A challenge for this theory was the lack of excess infrared radiation, typically emitted by warm dust from such collisions. Recent research, however, suggests smaller, cooler dust particles might be responsible.
The most sensational hypothesis proposed an “alien megastructure,” specifically a Dyson Swarm. A Dyson Swarm is a hypothetical collection of structures, like solar panels, built by an advanced civilization around a star to harness its energy. This theory was considered because the immense and irregular dimming events were difficult to explain by natural phenomena alone, leading some to consider an artificial origin. Scientists generally regard this as a last-resort explanation, favoring natural phenomena unless proven otherwise. Observations have largely disfavored the megastructure idea, especially with evidence showing the dimming affects different wavelengths of light unequally, consistent with dust rather than solid structures.
Less favored or largely disproven theories included instrumental error in the Kepler telescope, which was ruled out as data remained consistent across different detectors. Stellar activity, like large starspots, was also considered but found insufficient to explain the magnitude and duration of the dimming.
The Ongoing Scientific Quest
The mystery surrounding Tabby’s Star continues to drive astronomical inquiry, as a definitive, universally accepted explanation remains elusive. Scientists actively monitor the star using various telescopes to gather more data and test existing theories. New observations, including from the Spitzer Space Telescope and ground-based observatories, have provided crucial insights.
One significant finding is that Tabby’s Star’s dimming appears more pronounced in ultraviolet light than in infrared. This “wavelength-dependent dimming” indicates the objects blocking the light are likely very small particles, on the order of micrometers, such as dust. Larger, opaque objects like planets or solid megastructures would dim all wavelengths equally. This observation strongly disfavors the alien megastructure hypothesis and points towards dust as the primary cause.
While dust is increasingly considered the most likely culprit for the dimming, its exact source and mechanism are still debated. Theories suggest the dust could be from a ring of debris, repeated cometary outgassing events, or even the remnants of a planet consumed by the star long ago. The star continues to be observed for new dimming events, which provide opportunities to further refine these models.