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In 2015, astronomer Tabetha Boyajian and colleagues announced the discovery of about 1,500 light-years away. It came to be known as "Tabby's star" or "Boyajian's star," and the peculiar alterations in the light transmitted to Earth quickly drew attention.

Among other speculations, the idea of a megastructure around the star, such as a Dyson swarm, was scrutinized before it was ruled out as the cause of the peculiar dimming, although the cause of the long-term trend still remains unknown.

However, the idea of megastructures built around stars by advanced civilizations has remained of interest. In a study in , Brian C. Lacki of the Breakthrough Listen project in Oxford, UK asks "Even if every single star is home to intelligent life at some point during its lifespan, the odds are against us observing them unless the lifespan of the technosignatures is many millions of years." But he continues, "if they are short-lived, might some technosignatures greatly outlast their creators?"

As Earthbound civilizations have progressed, they have required increasing amounts of energy, and presumably this will be true of other civilizations in the universe.

After utilizing all the starlight incidents on their planet, extraterrestrials might seek to use all of their star's outputted energy by building a capturing megastructure around it, such as a Dyson sphere, a thin shell constructed by disassembling the planets and other massive bodies in their solar system.

When Dyson investigated the concept —crediting the original idea to British science fiction author Olaf Stapledon in 1937—he asserted that a rigid shell would be unstable, which was shown mathematically ; gravitational instabilities and material stresses far exceed the strongest materials and would quickly tear it apart.

However, a "Dyson swarm" could be built instead, a megastructure consisting of portions of a shell, satellites functioning as orbiting habitats or solar energy collectors.

If a Dyson megaswarm in our solar system covered even one-tenth of 1% of the spherical area at the Earth-sun distance, it would still capture two million times more solar power compared to all sunlight incidents on Earth alone.

As the "covering fraction" of the swarm approached 1, the civilization would become a Type II population on the Kardashev energy scale, with enormous amounts of power available to them.

There's another reason a species might build a megaswarm—to serve as a technosignature that communicates their presence to others in the galaxy, bridging not just cosmic distances, but, even if civilization disappears, eons of time.

The shell portions could have distinct shapes that would partially occult their star's outgoing light, akin to the popular by which astronomers have discovered most known exoplanets. But if their technical capabilities or entire civilization vanished, how long would the megaswarm stay in place?

Any such megaswarm would need a system of guidance control, active or automated, as it would be susceptible to collisions between its elements because other bodies in its solar system would exert slightly differing forces on each element.

If the control system began to fail in part or in whole—a seemingly inevitability due to technological breakdowns—gravitational instabilities will create collisions between the swarm members, then eventually a cascade of collisions, akin to how space junk is colliding (and will collide more often) in Earth's orbit, leading to a snowballing number of collisions called a Kessler syndrome, unless space debris is reduced by cleanups.

Lacki uses careful and creative geometrical and dynamical reasoning to analytically describe and predict the evolution of the elements in a potential megaswarm. Because the view of at least one element of a swarm of occulting, transiting elements should be capable of being seen from any angle, it should have a minimum number of elements (of the size of planets, but much thinner) that depends on their distance from their star and the radius of the star; for a star that is a twin of the sun at least 340 elements are needed.

For such a minimal swarm whose elements are randomized in velocity, Lacki calculates that the average time between element collisions would be a million years, but, because a few collisions happen long before the average time, the time to a "cascade" of collisions, when the swarm is ground down to fragments and dust, is only 41,000 years.

That's not very long if the intent of a future human-built swarm, say, is to signal our presence out to the galaxy long after we're gone. "Even if every solar analog hosted one of these swarms at 1 AU (astronomical unit) once during its lifespan," Lacki writes, "only one in twenty thousand might be expected to still have one unless they are actively maintained."

The cascading swarm destruction time increases greatly as the star's radius increases: for a red giant of one solar mass and 25 times the radius of the sun, it increases to 5.3 billion years, with a minimum swarm having 4,800 elements. By contrast, an M dwarf (red dwarf) whose mass and radius are, respectively, 0.2 and 0.1 times the sun, would have 11 minimal occulters and fragment in just over four months.

Lacki found that a better design would be positioning elements around rings around the star, with the rings increasing in radius, just like Earth's satellites are at different altitudes, from low-earth orbit to geosynchronous orbit. Intrabelt collisions would then be expected within tens of thousands of years.

In any case, Lacki concludes, "stellar megaswarms, without maintenance, are expected to be destroyed in most cases within a few million years," which he notes is about how long it would take an extraterrestrial intelligence to spread across a galaxy.

Among the forces that would work to destroy large megaswarms are radiation pressure from the star, the star's oblateness and gravitational perturbations from other bodies in the solar system. For example, Jupiter would cause the destruction of a megaswarm at Earth's orbit in just a few hundred thousand years, Lacki calculates.

He speculates that an advanced civilization, especially if using their swarm for solar power like a Kardashev II civilization would, might well strip all planets and asteroids from its solar system to minimize the chances of the swarm's destruction from gravitational perturbations.

A Kardeshev III civilization, aiming to capture all its galaxy's starlight, might strip all planets from the galaxy, leaving it otherwise barren and devoid of life. Once the galactic megaswarm is destroyed there will be no possibility of life restarting anywhere in that immense region of space.

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