Beta Ceti star, Chandra X-ray image. Beta Ceti is an incredibly strong X-ray source, about 2000 times more powerful than our Sun, located 9.5 light years away in the constellation Cetus. It has a mass of around 3 times our sun, but is only one twentieth the diameter. Its X-ray production is due to its fuel source; it is undergoing the fusion of helium to produce carbon. For much of its life it was similar to our own Sun, producing helium from hydrogen in its core. When this was exhausted it contracted and started fusing the hydrogen outside the core. This caused it to expand and become a red giant, until all its hydrogen was exhausted and it contracted again until it could fuse helium.