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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Tabby's Star | 3/5 | https://en.wikipedia.org/wiki/Tabby's_Star | reference | science, encyclopedia | 2026-05-05T04:16:04.645795+00:00 | kb-cron |
== Luminosity == Observations of the luminosity of the star by the Kepler space telescope show small, frequent, non-periodic dips in brightness, along with two large recorded dips in brightness two years apart. The amplitude of the changes in the star's brightness, and the aperiodicity of the changes, mean that this star is of particular interest for astronomers. The star's changes in brightness are consistent with many small masses orbiting the star in "tight formation". The first major dip, on 5 March 2011, reduced the star's brightness by up to 15%, and the next 726 days later (on 28 February 2013) by up to 22%. (A third dimming, around 8%, occurred 48 days later.) In comparison, a planet the size of Jupiter would only obscure a star of this size by 1%, indicating that whatever is blocking light during the star's major dips is not a planet, but rather something covering up to half the width of the star. Due to the failure of two of Kepler's reaction wheels, the star's predicted 750-day dip around February 2015 was not recorded. The light dips do not exhibit an obvious pattern. In addition to the day-long dimmings, a study of a century's worth of photographic plates suggests that the star has gradually faded in 100 years (from c. 1890 to c. 1990) by about 20%, which would be unprecedented for any F-type main-sequence star. Teasing accurate magnitudes from long-term photographic archives is a complex procedure, however, requiring adjustment for equipment changes, and is strongly dependent on the choice of comparison stars. Another study, examining the same photographic plates, concluded that the possible century-long dimming was likely a data artifact, and not a real astrophysical event. Another study from plates between 1895 and 1995 found strong evidence that the star has not dimmed, but kept a constant flux within a few percent, except an 8% dip on 24 October 1978, resulting in a period of the putative occulter of 738 days. A third study, using light measurements by the Kepler observatory over a four-year period, determined that Tabby's Star dimmed at about 0.34% per year before dimming more rapidly by about 2.5% in 200 days. It then returned to its previous slow fade rate. The same technique was used to study 193 stars in its vicinity and 355 stars similar in size and composition to Tabby's Star. None of these stars exhibited such dimming. In 2018, a possible 1,574-day (4.31-year) periodicity in dimming of the star was reported.
== Stellar companion == A red dwarf stellar companion at projected separation 880±10 AU from Tabby's Star was confirmed to be comoving in 2021. For comparison, this is around 180 times the orbit of Jupiter, around 30 times the orbit of Neptune, or around 5.3 times the distance to Voyager 1 as of January 2025.
== Hypotheses == Originally, and until Kohler's work of 2017, it was thought that, based on the spectrum and stellar type of Tabby's Star, its changes in brightness could not be attributed to intrinsic variability. Consequently, a few hypotheses have been proposed involving material orbiting the star and blocking its light, although none of these fully fit the observed data. Some of the proposed explanations involve interstellar dust, a series of giant planets with very large ring structures, a recently captured asteroid field, the system undergoing Late Heavy Bombardment, and an artificial megastructure orbiting the star. By 2018, the leading hypothesis was that the "missing" heat flux involved in the star's dimming could be stored within the star's interior. Such variations in luminosity might arise from a number of mechanisms affecting the efficiency of heat transport inside the star. However, in September 2019, astronomers reported that the observed dimmings of Tabby's Star may have been produced by fragments resulting from the disruption of an orphaned exomoon.
=== Circumstellar dust ring ===
Meng et al. (2017) suggested that, based on observational data of Tabby's Star from the Swift Gamma-Ray Burst Mission, Spitzer Space Telescope, and Belgian AstroLAB IRIS Observatory, only "microscopic fine-dust screens", originating from "circumstellar material", are able to disperse the starlight in the way detected in their measurements. Based on these studies, on 4 October 2017, NASA reported that the unusual dimming events of Tabby's Star are due to an "uneven ring of dust" orbiting the star. Although the explanation of a significant amount of small particles orbiting the star regards "long-term fading" as noted by Meng, the explanation also seems consistent with the week-long fadings found by amateur astronomer Bruce L. Gary and the Tabby Team, coordinated by astronomer Tabetha S. Boyajian, in more recent dimming events. A related, but more sophisticated, explanation of dimming events, involving a transiting "brown dwarf" in a 1600-day eccentric orbit near Tabby's Star, a "drop feature" in dimness, and predicted intervals of "brightening", has been proposed. Dimming and brightening events of Tabby's Star continue to be monitored; related light curves are updated and released frequently. Nonetheless, data similar to that observed for Tabby's Star, along with supporting data from the Chandra X-ray Observatory, were found with dust debris orbiting WD 1145+017, a white dwarf that also has unusual light curve fluctuations. Further, the highly variable star RZ Piscium, which brightens and dims erratically, has been found to emit excessive infrared radiation, suggesting that the star is surrounded by large amounts of gas and dust, possibly resulting from the destruction of local planets.
=== A cloud of disintegrating comets ===