Tabby's Star

The Transit view is one thing crossing the star, drawn honestly. The F3V disk is rendered with the same quadratic limb darkening the light curve is computed from, so the centre is brighter than the edge. Pick what crosses it: a planet, an opaque disk that takes about 1%; a comet swarm, a ragged string of fragments and dusty tails; a dust cloud, translucent and extended; or a Dyson swarm, a field of hexagonal collectors whose dip is set by a coverage slider. The scrolling strip at the bottom is the live light curve, and it is real: it is computed by occulting the disk, sample by weighted sample.

The Blue / Red toggle is the point of the whole instrument. Fine dust scatters short wavelengths more than long, so a dust transit runs deeper in blue; a solid body, a planet or a panel, blocks every colour equally. Switch bands and watch the Blue minus Red cell: a gap means dust, a flat zero means a disk. This is the logic of the 2018 measurement that reshaped the debate, put in your hands.

The Curve view is the whole story at once: the full Kepler light curve over 1580 days, flat at the top and then falling into D792 at 16%, the deep D1519 complex at 22%, the D1540 triple-dip and D1568 at 8%. Toggle the Montet & Simon secular fade and the 2017 ground-based dips, and click any deep dip to read its depth, duration and shape. A legend along the top says, plainly, which reading each feature supports.

This instrument presses the site's whole method onto a single star. Tabby's Star has no witness recording and no leaked file, only a public light curve anyone can pull from MAST and a question still unsettled: what is blocking its light. That makes it a proving ground. When the evidence is just numbers, with no stake and no insider, how do you weigh "dust" against "comets" against "an engineered swarm". The answer is not a verdict but a test: switch the band, and let colour speak. Summarise, attribute, link; the verdict, as always, is yours.

It is also where three sibling instruments meet. When Avi Loeb proposed a lightsail reading of ’Oumuamua, he leaned on the very physics we cost seriously in The Laser Sail: a large, thin, reflective structure. A Dyson swarm is that same idea scaled to a star. And whether this star has anyone around it runs straight into the silence in the last four factors of The Drake Equation: SETI pointed its telescopes here, and the radio, the laser and the infrared all came back empty. After this instrument, you will know better what that silence weighs.

One idea runs the whole instrument: a transit is the fraction of a star’s light an occulter removes, weighted by how bright the disk is where it sits.

depth = 1 − ( ∫ I(μ) · T(x,y) dA ) / ( ∫ I(μ) dA ) · with · I(μ) = 1 − u₁(1−μ) − u₂(1−μ)² · u₁ = 0.32 · u₂ = 0.30

Limb darkening sets the shape. A star is a ball of gas, brightest where you look straight down into it (the centre) and dimmer toward the edge, where your line of sight grazes cooler, higher layers. The instrument uses the standard quadratic law for an F3V star, so an occulter crossing the centre takes more light than the same occulter crossing the edge. That is why even a planet’s tiny dip has a rounded, not flat, bottom.

Opaque bodies block; dust attenuates. A planet or a panel removes 100% of the light behind it: the depth is just the covering fraction, weighted by limb darkening, and it is the same in every colour. A dust cloud only dims what passes through it, by a factor exp(−τ), and its optical depth τ is larger in blue than red for sub-micron grains. That single difference is the colour test.

The light curve is computed, not drawn. The disk is sampled at 1600 points, each weighted by its limb-darkened brightness. Every frame, the moving occulters are projected onto the disk and each sample is marked blocked, attenuated or clear. Summing gives the instantaneous flux. Nothing about the dip is hand-animated; change the scenario or the band and the curve recomputes from the geometry.

The Curve view is the real record, modelled. The full Kepler light curve is rebuilt by superposing analytic dip profiles fit to the published depths and timings (Boyajian et al. 2016): symmetric for the shallow events, asymmetric for D792 (a slow ingress, a fast egress), a close triple for D1540. The secular fade follows Montet & Simon 2016. It is a faithful reconstruction of the data, tuned to match the paper.

The evidence is tagged as you go. The bottom-left table is the conscience of the sim. The Kepler curve, the depths, the 2018 colours and the empty SETI and infrared searches are MEASURED; this reconstruction and the dust and swarm models are MODELLED; which explanation you favour is a READING. Rows light up as you touch the matching control, so you always know which kind of claim you are looking at.

The photometry is measured; the colour result is measured; the empty searches are measured. The reconstruction and the optical models are modelled. Which of dust, comets, debris or a swarm is doing it is a reading, and the colour test points hard at dust. The staging, a star sitting still while one tidy object crosses it once, is the only liberty, and it is labelled where it happens.

Four scenarios, from the mundane to the famous, each computed the same way so you can compare them fairly.

• Planet. An opaque, Jupiter-sized disk. The dip is symmetric, rounded by limb darkening, and about 1%, the ceiling for any planet. It is here to set the scale the deep dips break.
• Comet swarm. A clumpy string of fragments trailing dust. The dips are shallow, irregular and asymmetric, a few percent, and the tails add a faint colour. This is Bodman & Quillen’s 2016 model in miniature.
• Dust cloud. A translucent, extended cloud. The dip is deep and, crucially, deeper in blue than red. This is the leading explanation, and the one the band toggle was built to show.
• Dyson swarm. A field of opaque hexagonal collectors, with a coverage slider from nothing to half the disk. The dip depth just tracks the covering fraction, and it is achromatic, which is exactly why the 2018 colour result weighs against it.

Every serious explanation on the record, with who put it forward and where it stands. Neutral, attributed, and no verdict: the reading is yours.

1. Run the colour test. Set the scenario to Dust, watch the blue dip, then switch to Red and watch it shrink. Now do the same on Planet or Dyson: nothing moves. The Blue minus Red cell is the whole 2018 result in one number.
2. Find the ceiling. Switch to Planet and read the depth: about 1%. Then open the Curve view and look at D1519 at 22%. Twenty times a planet. That gap is why the story ever needed comets, debris or a swarm.
3. Build a swarm. On the Dyson scenario, drag coverage from 0 to 50% and watch the dip depth follow it one for one. Then switch bands: it stays flat. A swarm can make the depths, but it cannot make the colours.
4. Read D792. In the Curve view, click the first deep dip. It is asymmetric: a slow week-long fade, then a fast recovery. No planet is that lopsided. That asymmetry is the first clue that something with structure crossed the star.
5. Add the fade. Toggle the Montet & Simon secular fade in the Curve view. The whole baseline droops by a few percent across the mission. Dust explains both the dips and the fade; that is part of why it leads.
6. End on the Evidence. Touch the band toggle and watch the colour row flash MEASURED; switch to the Dyson swarm and watch its row flash READING. The tags are the point: the same star, different kinds of claim.

The honest line between what has been measured, what is modelled here, and what is a reading:

In one line: the Kepler light curve, the dip depths and timings, the 2018 result that the dips are deeper in blue, and the empty radio, laser and infrared searches are all measured; this reconstruction and the dust and swarm models are modelled from those measurements; and which of dust, comets, debris or a swarm is doing it is a reading, on which the colour test points hard at fine dust and nothing formally excludes a swarm. The instrument takes no side.

• Boyajian, T. S., et al. (2016). Planet Hunters IX. KIC 8462852, where’s the flux? MNRAS 457, 3988. arXiv:1509.03622. The discovery paper: the dips, the depths, the absence of a period.
• Wright, J. T., et al. (2016). The Ĝ Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. ApJ 816, 17. arXiv:1510.04606. The framing that put a Dyson swarm on the table, and how to test it.
• Marengo, M., Hulsebus, A., & Willis, S. (2015). KIC 8462852: The Infrared Flux. ApJL 814, L15. No warm-dust or waste-heat excess in WISE.
• Harp, G. R., et al. (2016). Radio SETI Observations of the Anomalous Star KIC 8462852. ApJ 825, 155. arXiv:1511.01606. The Allen Telescope Array listened; nothing.
• Schuetz, M., et al. (2016). Optical SETI Observations of the Anomalous Star KIC 8462852. ApJL 825, L5. arXiv:1602.00987. A search for laser pulses; nothing.
• Montet, B. T., & Simon, J. D. (2016). KIC 8462852 Faded Throughout the Kepler Mission. ApJL 830, L39. arXiv:1608.01316. The secular fade across the four years of data.
• Schaefer, B. E. (2016). KIC 8462852 Faded at an Average Rate of 0.165 Magnitudes per Century from 1890 to 1989. ApJL 822, L34. arXiv:1601.03256. The contested century-long dimming.
• Hippke, M., et al. (2016). Reproduction of the KIC 8462852 Century-Long Dimming with the DASCH Data. arXiv:1601.07314. The rebuttal: an artefact of the plate archive.
• Bodman, E. H. L., & Quillen, A. (2016). KIC 8462852: Transit of a Large Comet Family. ApJL 819, L34. The exocomet-swarm model.
• Metzger, B. D., Shen, K. J., & Stone, N. (2017). Secular dimming of KIC 8462852 following its consumption of a planet. MNRAS 468, 4399. arXiv:1612.07332. The consumed-planet reading.
• Boyajian, T. S., et al. (2018). The First Post-Kepler Brightness Dips of KIC 8462852. ApJL 853, L8. arXiv:1801.00732. The colour test: the 2017 dips are deeper in blue. Fine dust, not a solid object.
• Deeg, H. J., et al. (2018). Non-grey dimming events of KIC 8462852 from GTC spectrophotometry. A&A 610, L12. Independent confirmation of the chromatic dips.
• Dyson, F. J. (1960). Search for Artificial Stellar Sources of Infrared Radiation. Science 131, 1667. The original: a swarm of collectors, and the waste heat to look for.