New study finds seven potential Dyson Sphere megastructure candidates in the Milky Way - Dyson spheres, theoretical megastructures proposed by physicist Freeman Dyson in 1960, were hypothesised to be constructed by advanced civilisations to harvest the energy of host stars.

The mass from a Dyson Sphere is generally assumed to be heavy elements lifted from the star. Lifting heavy elements from your star massively extends its lifetime as well you. The evolution to Dyson spheres (aka Dyson Swarms) makes a lot sense

1. Today we have solar panels on our planet

2. As heavy industry moves to space we are likely to put an increasing number of solar panels in orbit around the sun to meet our off planet energy needs.

3. As our sun ages, we are likely to filter out heavy elements from our sun to extend its lifetime. These filtered out elements will end up orbiting the sun. Why not use them for more solar collectors.

4. Much like plants in s forest this swarm of energy collecting satellites will likely attempt to maximize the sun light it collects, occluding the a sizable percentage of the suns output. 

Since stars represent 99% of the mass in a solar system. The size of this swarm of satellites is likely to be very very big for a very old civilization.