A strange star located 1,500 light-years from Earth is exhibiting strange flickering behavior that’s leading some scientists to speculate that an alien megastructure is blocking the light. But what would such a structure be exactly and how likely is it that the Kepler space telescope has actually spotted one?
Right now the star KIC 8462852 is really hot – and not just because it is a F-type star – but because the Kepler space telescope has discovered that it flickers in a highly unusual way, as if something is obscuring it. These dips in the light are different to what you would expect from planets blocking the star.
Scientists are failing to come up with an explanation for the phenomenon based on natural astrophysical processes, so attention has turned to the potential of an alien megastructure blocking the light. But what would such a structure be exactly and how likely is it that Kepler has spotted one?
It is true that dips in the light from the star are odd, both in shape and timing. They are unlikely to be caused by a surrounding cloud of dust, as the star is too old to have such a planet-forming disk. But what about a storm of comets? They are actually not very good at obscuring stars, so it is not all that likely either. Fragments from a planetary collision might work, except that such events are so rare that we would not expect to see any with Kepler.
The lack of a simple explanation has made a lot of people quietly (or not so quietly) ask whether this could be an alien megastructure, known as a Dyson sphere.
The Dyson sphere was first described by Freeman Dyson in the 1960s, who argued that a technologically advanced alien civilisation would use more and more energy as it grew. As the biggest source of energy in any solar system is the star at its centre, it would make sense that the civilisation would build orbiting solar panels to try to capture it. Such structures would take up more and more space until they eventually covered the entire star like a sphere. However, a complete sphere would be invisible to Kepler as it would absorb all of the light from the star, so signs of this would have to come from something currently under construction.
Could this be the case? I doubt it. My basic argument is this: if a civilisation builds a Dyson sphere, the sphere is unlikely to remain small for a long period of time. Just as planetary collisions are so rare that we should not expect to see any with Kepler, the time it takes to make a Dyson sphere is also very short: seeing it during construction is very unlikely. Even if we knew a Dyson sphere would eventually be built in a solar system the chance of actually witnessing it happening is low.
How do we know this? To build a Dyson sphere, one would need to disassemble a nearby body, like a planet, to provide the material for the solar captors. In a recent paper written with a colleague, we calculated that disassembling Mercury to make a partial Dyson shell could be done in 31 years. One way of doing this would be to mechanically disassemble the planet, much like we do in our aluminium and steel industries. From these industries, we know a lot already about the energy cost of such work, so the trick is to use already mined material to build more mining equipment and solar collectors to power it, achieving an exponential feedback loop.
The time it would take to disassemble any terrestrial planets is not much longer than for Mercury, while the gas giants would take a few centuries. Our aim in the paper was to show that using a small fraction of the resources in the solar system it is possible to harness enough energy to launch a massive space colonisation effort (literally reaching every reachable galaxy, eventually each solar system), but the important point is that this kind of planetary engineering is fast on astronomical timescales.
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