A new image from the Hubble Space Telescope shows a small dwarf galaxy called IC 3430 that’s located 45 million light-years away. This galaxy is classified as both a dwarf galaxy, because of its small size, and an elliptical galaxy, because of its form.
Elliptical galaxies are smooth and featureless, appearing blob-like and diffuse, unlike spiral galaxies, like our Milky Way, which have a distinct structure of a central hub and stretching spiral arms.
In this image, you can see the smooth oval shape of IC 3430. Elliptical galaxies are primarily composed of older stars, as they lack the gas required to form new stars, but in this case, you can see a core of hot blue stars in the center of the galaxy. These hot stars are younger, which is a rarity for elliptical galaxies.
This other recent Hubble image also shows a dwarf galaxy, one called NGC 5238. This one is located 14.5 million light-years away, but has a different and more complex type of structure. It has glowing spots of brighter areas, which are groups of stars called globular clusters.
The structure of this galaxy gives clues to its history. Astronomers think that the structure comes from a historical merger, when another galaxy wandered too close to this galaxy and the two merged into one. This caused pockets of stars to form due to gravitational disturbances pushing and pulling at the gas.
Indications of a historical merger include groups of stars within a galaxy with different chemical properties, suggesting they formed in a different environment from their neighbors. By studying smaller galaxies like this one, astronomers can build up their understanding of how galaxies form and merge.
“One main theory of galaxy evolution is that galaxies formed ‘bottom-up’ in a hierarchical fashion: star clusters and small galaxies were the first to form out of gas and dark matter,” Hubble scientists explain in a press release accompanying this image. “Over time, gravity gradually assembled these smaller objects into galaxy clusters and superclusters, which explains the shape of the largest structures we see in the universe today.”