This May Be the Best Explanation Yet For That Mysterious 'Alien Megastructure'
A new paper from Columbia University suggests that Tabby's star-the celestial object voted most likely to host an alien megastructure-is acting weirdly because it recently annihilated an entire planet, and the shattered remains of that planet are now producing strange flickering effects. It's probably the best theory we've heard so far.
It's not aliens.
At least that's the conclusion reached by a trio of astronomers from Columbia's Departments of Physics and
Trouble is, none of these theories can explain the double-whammy of anomalies, i.e. the odd short-term flickers
the gradual, long-term dimming. The new theory by Metzger and his colleagues does just that.
The researchers hypothesize that a planet recently plunged into KIC 8462852. The gravitational energy produced by the collision would have boosted the star's normal nuclear energy production, causing it to brighten rapidly and then slowly decay over time. If this idea is correct, then we happen to be observing Tabby's star as it returns to its normal level of luminosity.
This theory may also help to explain the star's sudden dips in light. Following the collision, portions of the planet (and possibly bits of its moon or moons) entered into eccentric orbits. Every time this debris field moves in front of the star (from our vantage point), it appears to flicker.
As for the size of the planet, the researchers say that depends on when the impact occurred. "If the planet was Jupiter-sized, then the disruption would have taken place about 1,000 years ago in order to explain the rate of dimming observed today," Metzger told Gizmodo "On the other hand, if the object was the size of the Moon, then the brightening and dimming would have taken place about a decade ago." Metzger says a collision with a moon-like object probably wouldn't produce the observed century-long dimming, but it could explain the dimming seen during four years of Kepler observations.
The researchers say they're "agnostic" about the source of the object or objects that fell into Tabby's star. "We could imagine many smaller objects in succession, or one big one a fairly long time ago," said Metzger. "It's hard to tell at this late of stage, although maybe the orbiting debris can provide some clues."
According to Stone, the collision likely didn't happen overnight. "The planet may have spent millions of years slowly decreasing its pericenter [closest approach to Tabby's star on its orbit] before it finally impacted the star, causing a brightening and then the slow dimming we have observed," he told Gizmodo. "Towards the end of this slow process...any moons around the planet would have been detached by the tidal field of Tabby's star." Given that gas giants like Jupiter and Saturn host dozens of fairly large icy moons, that's a lot of potential material to be added to the orbiting debris cloud.
"Moreover, these moons now have pericenters around the star that are closer than the orbit of Mercury around our own Sun, so if they have icy outer layers, they should be evaporating and outgassing rapidly, blowing clouds of vapor and dust off their surfaces," Stone continued. "The dust in these expanding evaporation clouds may be able to explain the irregular transits of Tabby's Star seen by Kepler." Alternately, the tidal heating of the detached moons could be creating enormous clouds of dust.
The fact that we're seeing the late stages of a collision-an extremely transitory episode by cosmological standards-suggests that events like these are common. Kepler has observed around 100,000
The good news about this theory is that it's testable. Metzger says the next time we see a big dip in the luminosity of Tabby's star, we should expect to see significant amounts of gas and dust released from the debris field. "This should produce a temporary flare of infrared emission (as the dust is heated) lasting for a few days to a few weeks," Metzger told Gizmodo.
Another way to prove this theory would be to actually watch a moon or planet smash into a star. Such an event should produce a temporary brightening, followed by another period of steadily decreasing luminosity.
It's an intriguing theory, and one that makes a hell of a lot of sense. It's not an open-and-shut case, but thanks to studies like this, we're getting increasingly close to solving this fascinating mystery.