Just for the absurdity of it let me try to engage you in discussion. In the center of our solar system is a star that we call the sun. The volume of the sun is about 1,000,000 times the volume of the earth. The sun is primarily hydrogen. The light and heat are primarily from the fusion of hydrogen into helium. When the sun (and stars of similar size) uses up its hydrogen it will be eventually become a very dense white dwarf. Mercury is a tiny rocky planet and cannot possible be the remnants of a star. The planet Mercury which is about 1.5 times the diameter of the moon is not full of radiation. Since you call Mercury the first Sun. Is the actual Sun the third Sun? You realize that the milkyway galaxy (our galaxy) is made up of hundreds of billions of stars? By chance do you mean that the Second sun (what ever that is) is on the edge of our solar system?