Not much is known about the Devourer of Worlds, (or DOW) as very few have lived to see it and talk about it. It is mostly dismissed as a rumor, but it does indeed exist. The DOW is an enormous whale-like creature about 50,000 miles long, about half as long as a standard gas giant. So far, only one is know and dwells around the outermost edges of the galaxy. No one also knows what its biochemistry is and how it is able to survive in space, though many hypothesize that it is silicon-based. It is also completely unknown how long the DOW lives if it even is able to die nor are its origins known.
Mostly, the DOW feeds on asteroids and nebulae, but it is dangerous in that its mouth is large enough to swallow small, terrestrial planets. Its rough hide is impervious to nearly any missiles or lasers, so if the DOW is approaching a planet, the only way to avoid death is to leave the planet before it gets swallowed. Rumor has it that when a planet is swallowed, the whole sky goes dark and the world is exhausted of its nutrients. It is also believed that the DOW feeds on emotions such as panic and despair so the digestive process is quite slow. However, due to the lack of sunlight, most life on the planet dies before it actually does get derived of nutrients.
Because of the vast distances required, the DOW takes advantage of every possible source of nutrients in the solar system: gas giant moons, planets, asteroids, and even some gas giants itself. Once it has devoured almost all celestial objects in the solar system, it will have enough food to survive the trip to the next solar system.
The DOW can move quite fast. It is believed flatulence is what can propel it to the speed of light. Many scientists ridicule the idea for being far-fetched, but there is no other explanation. This is the fastest it can travel so it needs to save up food for the trips in between systems.
Many are worried if nothing is done about the nigh-invincible DOW, it will eventually swallow every single celestial body in the galaxy, leaving only lonely stars. However, at the pace the DOW moves, such an event will not occur for hundreds of thousands of years. Despite, any planet with life on it that is in close proximity to the DOW is at risk.