Tabby’s Star is probably not home to an advanced alien civilization. The star’s dimming isn’t being caused by some massive alien structure. At least, not the long-term dimming trend. Instead, new research suggests the most likely culprit is dust.

Officially designated KIC 8462852, the star made headlines after researchers announced significant short-term dimming. NASA’s Kepler space telescope observed the star dimming by up to 20% over just a few days. But the star is also in a longer-term dimming cycle. A cycle that continues today.

Researchers still struggle to explain the extreme short-term dimming, but they have a good explanation for the longer-term trend. Dust.

Using NASA’s Spitzer and Swift missions, researchers found dimming was less in infrared light compared to ultraviolet light. According to the researchers, “any object larger than dust particles would dim all wavelengths of light equally.” That nixes a giant alien structure harnessing the star’s power.

“This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming,” says Huan Meng, the research’s lead author. “We suspect, instead, there is a cloud of dust orbiting the star with a roughly 700-day orbital period.”

Think of Tabby’s Star dimming like how we experience the Sun every day. At noon, the Sun beats down on you. Find a tree or overhang and the amount of sunlight hitting you is reduced across all wavelengths. Now think about sunrise or sunset. The sun appears redder as ultraviolet light is scattered by tiny particles in Earth’s atmosphere. This effect is even more pronounced when the particles are thicker like smoke from a nearby forest fire.

Based on the observations, the dust causing this dimming is exceptionally tiny. Each grain no more than a few micrometers across. Any smaller and the pressure from the starlight would continuously push the dust into space. Anything bigger than a dust particle would uniformly block light in all wavelengths according to the researchers.

This isn’t a slam dunk for what’s causing the dimming. Only the best explanation given the observations. It does pretty much rule out an alien megastructure. That was always one of the more ‘out-there’ ideas, but it made for fun speculation.

There’s still the question of what caused the star to suddenly dim around 20% during the Kepler observation. Previous research pointed the finger at a possible swarm of comets. But Siegfried Vanaverbeke, a volunteer at the Belgian AstroLAB IRIS observatory (who assisted with this new research), suggests, “Tabby’s Star could have something like a solar activity cycle.”

There’s still a lot of mystery surrounding Tabby’s Star. But, researchers are pretty sure an advanced alien civilization isn’t harnessing the star’s power. And if they are, let’s maybe not let them know where we are.

Tabby’s Star joins an ever-growing list of observation targets for the next generation of telescopes.

Top illustration by NASA/JPL-Caltech


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