DOOMSTAR

Belmont SF paperback, Jan 1966. Cover artist uncredited.

"The sun shone brightly on this fateful morning, bringing to its planets warmth and life-giving rays. The brightness increased sharply as the morning grew older. The glare was blinding; the radiation not life-giving, but deadly. By mid-afternoon the brilliant, intense sun shone on barren space. It had blasted each of its four planets out of existence. 

Someone had found a way to poison a star. 

And someone had to be found who could prevent the takeover - or destruction - of the entire universe. Who? Johnny Kettrick, as improbably a hero as there never was. Johnny Kettrick was banned from the cluster world for his not-too-honest dealings was sent back there with his three equally unholy partners to search out the doomstar...To find the Doomstar before it burned out another world."