A galaxy is a massive, gravitationally bound system of stars and stellar remnants, gas, dust, and the mysterious dark matter. The word galaxy is derived from the Greek galaxias (γαλαξίας), literally “milky”, a reference to our Milky Way galaxy. Examples of galaxies range from dwarfs with as few as ten million stars to giants with a hundred trillion stars.
Blogger kfc reports for Technology Review, March 20, 2012, that galaxies essentially have three different shapes:
- The vast majority are flattened discs, often with spiral arms.
- Some galaxies are ellipsoids, like rugby balls.
- A few galaxies are completely irregular with no symmetry.
So the discovery of a rectangular galaxy is bound to generate a flutter of interest.
Alister Graham at Swinburne University of Technology in Australia and a few mates discovered a dwarf galaxy designated LEDA 074886 in the constellation of Eridanus, which is shaped like an emerald cut diamond.
The galaxy sits in a group of about 250 dwarf galaxies some 21 megaparsecs from Earth in the constellation of Eridanus. It’s just a nipper, with a mass some 10 billion times that of the Sun. By contrast, the Milky Way is about a thousand times heavier.
The obvious question is how did it form. Graham and co think the emerald cut galaxy formed from the merger of two disc galaxies, like a couple of pancakes on top of each other. From the side, this looks rectangular.
That’s clearly a rare type of event but not entirely unknown. Graham and co say astronomers have discovered seven other rectangular examples out of the many millions of galaxies they’ve catalogued.
However, we may not have to look far to find another exotic shape. A couple of years ago, astronomers said they’d found evidence that the arms of the Milky Way were straightish, giving our galaxy a distinctly square look, like the Pinwheel galaxy, M101.