Almost every galaxy can be classified as a spiral, elliptical, or irregular galaxy. Only 1-in-10,000 galaxies fall into the rarest category of all: ring galaxies. With a dense core consisting of old stars, and a circular or elliptical ring consisting of bright, blue, young stars, the first ring was only discovered in 1950: Hoag's object. After decades of wondering how these objects form, we've seen enough of them, capturing them in various stages of evolution, that we finally know where they come from.
When we look out into deep space, beyond the confines of the Milky Way, we find that the Universe isn’t quite so empty. Galaxies — small and large, near and far, in rich clusters and in near-total isolation — fill the abyss of space, with the Milky Way being just one of approximately two trillion such galaxies within the observable Universe.
Galaxies are collections of normal matter, including plasmas, gas, dust, planets, and most prominently, stars. It’s through the examination of that starlight that we’ve learned the most about the physical properties of galaxies, and been able to reconstruct how they came to be.
In general, there are four classes of galaxies that we see. Spirals, like the Milky Way, are the most common type of large galaxy in the Universe. Ellipticals, like M87, are the largest and most common type of galaxy in the rich, central regions of galaxy clusters. Irregular galaxies are a third ubiquitous type, usually distorted from a prior spiral or elliptical shape by gravitational interactions.
But there’s a very rare type that’s striking and beautiful: ring galaxies. They make up only 1-in-10,000 of all the galaxies out there, with the first one, Hoag’s object, only discovered in 1950. After more than 70 years, we’ve finally figured out how the Universe makes them. READ MORE...
