Well it seems the whole mission of Black Hand and the Black Lanterns is to "reclaim those who have cheated death" such as Superman, Green Lantern, Hawkman, Hawkgirl, Kid Flash, Barry Allen, Superboy and so forth. It's those characters that end up dead but then somehow come back to life. And it seems the Hearts of those who perish help power up the Black Lantern's. It seems that the DC Universe is in for some major trouble because how can you kill something that is already dead?