Proposed by physicist Freeman Dyson in 1960, a Dyson sphere is a speculative megastructure that harvests a star's energy by partially or completely surrounding the star. It was considered as the hallmark of an advanced civilization, which is capable of traveling and colonizing all planets within a star system.
In the last couple of years, scientists suspected that KIC 8462852, a star over 1,400 light-years away, could be covered by a Dyson sphere built by an alien civilization. Because its brightness fluctuates in an unpredictable pattern. Later, that speculation dissipated as evidence suggested that the cause of brightness dimming could be rings of stellar dust.
Although it is tantalizing to imagine a structure that can enclose the whole or a large part of a star like our Sun, building one would require materials that are equivalent to, if not surpassing, the total mass of the solar system. Not to mention the amount of energy needed for such a megaproject. Alternatively, constructing a swarm or a fleet of star-orbiting satellites that is capable of harvesting and redirecting energy to planets make more sense.
Source: Kurzgesagt in a nutshell via Youtube