Like people, these galaxies are shaped by their environment, which explains the different shapes we see, says Karen Masters. He is an astrophysicist at Haverford College and a scientist at Galaxy Zoo, a citizen science program that classifies different types of galaxies. “There’s a lot of variety out there in the universe,” Masters tells Inverse. Spiral galaxies are circular in shape like a Blu-Ray, while elliptical galaxies look like a pigskin American football. Dwarf galaxies, which are much less massive than spirals or ellipticals, tend to be much more irregular, he says. A key step in thinking about the shapes of galaxies is understanding how they fit into the environment around them. To the Masters, these galaxies are somewhat like building blocks. “Sometimes I think of them as fairies lighting up the branches of the tree, where the branches are kind of the underlying infrastructure that we have,” he says. The infrastructure he refers to is dark matter, which is concentrations of mass that are invisible to the telescopes we use. We can, however, infer the presence of dark matter because of the gravitational effects it produces on the matter we can see. A common phenomenon that dark matter produces is the distortion of light, as NASA’s Jet Propulsion Laboratory explained on a website. “As light from distant galaxies travels towards us, it must pass through the gravitational fields of other galaxies. Therefore, we see distorted images of distant galaxies,” JPL said. “Ordinary matter does not account for the amount of distortion that astronomers observe.” The three main types of galaxies — with many dwarf galaxies belonging to irregulars. A. Feild (STScI) Galaxies have huge concentrations of dark matter that also causes them to gravitationally pull each other, Masters says. “There will be galaxies that gobble up small galaxies,” he says, citing the Milky Way’s long history as an example. The Galaxy is also on a potential collision course with a large neighbor, the Andromeda Galaxy. Another important clue to the shape of a galaxy is when it formed. When the universe was smaller and in an earlier stage of expansion after the Big Bang, mergers were much more common because galaxies interacted more often, Masters says. Gas was also quite abundant in these younger galaxies, leading to more potential materials for the galaxies to use during these mergers. These days, about 13.8 billion years after the creation of the universe, most galaxies are changing more slowly. Internal changes lead to the appearance of structures such as rod shapes. However, mergers still occur, albeit less frequently than before. The orbits of stars can also affect the shape of a galaxy through various “density waves,” which occur as material squeezes into galaxies in what amounts to a traffic jam, Masters says. This is because the orbits do not happen regularly and the stars can get stuck together due to their mutual gravity affecting each other. In contrast, supermassive black holes embedded in many galactic centers don’t seem to have a significant effect on how a galaxy is formed, since black holes are so small relative to a galaxy’s mass, Masters adds. Since galaxies come in so many different varieties of shape in the big three (ellipses, spirals and dwarfs), Masters says Galaxy Zoo is still important in classifying these different types. While machine learning makes computers more adept at selecting galaxy types, human intervention is good for putting findings into the big picture. As observatories like the James Webb Space Telescope gather observations, Masters says, the numbers and types of galaxies we see will increase. The community, he added, is very excited about the high-resolution views of early galaxies that Webb will provide when it completes commissioning this summer. LEARN SOMETHING NEW EVERY DAY.
