"It should have been discovered before," Sydney University astrophysicist Peter Tuthill said.

Along with James Lloyd of Cornell University in Ithaca, New York, Dr Tuthill found the previously unknown celestial object while studying a well-known star called MWC 922.

The star is located roughly 5000 light-years away. A light-year is 9.46 trillion kilometres.

"It's so nearly square that people probably mistook it for an aberration of the telescope," Dr Tuthill suggests.

By combining extremely high-resolution, near-infrared images of the star -- taken by the Mt Palomar Hale telescope in California and the Keck-2 telescope in Hawaii -- they realised that MWC 922 was the core of a nebula, an object formed by gas, dust and a central star.

According to Dr Tuthill, the regularity and intricate linear form of the nebula make it one of the most symmetrical objects ever found. Known as a "bipolar nebula", it has twin cones of out-flowing winds, shaped like two cocktail glasses placed stem to stem.

Lying across the "rim" of each glass is a linear structure resembling a pocket comb. A line runs like an equator from the right-hand side of one rim to the right-hand side of the other.

The nebula is significant as it's similar to another bipolar nebula, the Red Rectangle. Astronomers have been looking for a similar object since it was discovered 30 years ago.

Dr Lloyd and Dr Tuthill speculated in a report in the journal Science that conditions required to form these mirror-image structures may not be as rare as believed. They also said the striking ring system that formed around the supernova discovered in 1987 may have emerged from a progenitor system like the Red Square nebula.

"Discoveries as beautiful and interesting as this one don't come around very often in astronomy," Dr Tuthill said.