Eshems Nebula

Not much is known about Eshems Nebula except that it's located several lightyears from Cybertron and could be home to aliens who want to possess the AllSpark.

Fiction

IDW movie comics

Starscream ran afoul of an alien scout ship in the Nebula and presumably destroyed it, noting that it was the fourth one spotted in that area. Shortly after, green-skinned aliens massed a fleet in the nebula and took off for Cybertron. Their objective: the AllSpark. Defiance #1

After the devastating alien attack, Megatron led a Cybertronian force back to the nebula and attacked the alien fleet. After killing the captain of the alien flagship personally, Megatron ordered Starscream that there were to be no survivors. Defiance #2

Much later, after the war between Autobots and Decepticons had raged for eons, Optimus Prime launched the AllSpark into space to keep it from Megatron's clutches. Megatron pursued it into the Eshems Nebula and beyond. The Reign of Starscream #1

The AllSpark Almanac

The Eshems Nebula was a region of space bordered by the Autobot Commonwealth and the Quintesson Pan Galactic Co-Prosperity Sphere in the Milky Way. The Ejoornian fleet makes its home here. The AllSpark Almanac II Blackarachnia described the sensor array that she installed on the Nemesis as the most sophisticated "this side of the Eshems Nebula". The AllSpark Almanac