Beginning in 1610, when famed Renaissance polymath Galileo Galilei observed the night sky using a telescope of his own manufacture, astronomers gradually realized that our Solar System is part of a vast collection of stars known today as the Milky Way Galaxy. By the 20th century, astronomers had a good idea of its size and structure, which consisted of a central “bulge” surrounded by an extended disk with spiral arms. Despite all we’ve learned, determining the true morphology of the Milky Way has remained a challenge for astronomers.
Since we, the observers, are embedded in the Milky Way’s disk, we cannot see through the center and observe what’s on the other side. Using various methods, though, astronomers are getting closer to recreating what a “birds-eye” view of the galaxy would look like. For instance, a team of researchers from the Chinese Academy of Sciences (CAS) used the precise locations of very young objects in our galaxy (for the first time) to measure the morphology of the Milky Way. This revealed a multiple-arm morphology consisting of two symmetrical arms in the inner region and many irregular ones in the outer region.
In the 17th century, Galileo Galilee aimed his telescope at the stars and demonstrated (for the first time) that the Milky Way was not a nebulous band but a collection of distant stars. This led to the discovery that our Sun was merely one of the countless stars in a much larger structure: the Milky Way Galaxy. By the 18th century, William Herschel became the first astronomer to create a map that attempted to capture the shape of the Milky Way. Even after all that time and discovery, astronomers are still plagued by the problem of perspective.
While we have been able to characterize galaxies we see across the cosmos with relative ease, it is difficult for astronomers to study the size, shape, and population of the Milky Way because of how our Solar System is embedded in its disk. Luckily, there are methods to circumvent this problem of perspective, which have provided astronomers with clues to these questions. In a recent paper, a team from the Astronomical Observatory at the University of Warsaw (AstroUW) used a large collection of Mira variable stars to trace the shape of the Milky Way, which yielded some interesting results!
Science revealed to us that universe as we know it, is composed of billions of galaxies like our own Milky Way. When you consider how many stars are just in our own galaxy you can get just a small idea how big our universe really is. Despite this astronomers have made great strides in learning more about the galaxies and their different characteristics. One aspect that was defined early was their shapes. Thanks to the work of famous astronomer Edwin Hubble we know that just about any galaxy in the universe will have one of 4 different shapes, spiral, elliptical, lenticular, and irregular.
Spiral galaxies are one of the most familiar galaxy shapes. In fact when most people think of a galaxy, this type of galaxy shape is the first to come to mind. This is because the Milky Way is a prime example of a spiral galaxy. A spiral galaxy looks like a pinwheel. It is basically the nucleus with its different “arms” spiraling outwards. Spiral galaxies can be tight or loose to varying degrees. One important fact about spiral galaxies is that young stars are formed in the outer arms while older stars are found near the center.
The next two types of galaxies are elliptical and lenticular shaped galaxies. These types are the kinds that are the most similar. First they have few or no dust lanes and are largely composed of older mature stars. These types seldom have star forming areas. Of the four galaxy shapes this is the most cohesive and organized.
The final galaxy shape is the irregular galaxy shape. Irregulars have an indeterminate shape. These galaxies are often small and don’t have enough gravitational force to organize into a more regular form. The Hubble telescope has taken images of famous irregular galaxies like the Magellanic Clouds. Irregular galaxies can also be large galaxies that have undergone a major gravitational disturbance.
As you now see the four basic galaxy shapes seem to cover just about every type of galaxy out there. Like any classification of shape there are also subcategories. An interesting observation recently made about the shape of galaxies is the role that their formation plays in determining their shape. It is now thought that galaxies get their shape as they naturally develop, merge with other galaxies or disrupt each other’s path. This is another great mystery as we don’t currently have the technology to plot out the complete paths of galaxies in the universe.
We have written many articles about galaxy shapes for Universe Today. Here’s an article about irregular galaxy, and here’s an article about spiral galaxy.