They found that older stars tend to move on circular orbits around the galaxy's center, while younger stars are more likely to have elliptical orbits. This difference is thought to be due to the effects of dynamical friction, which is a force that causes objects moving through a medium to slow down due to interactions with the particles in the medium.
In this case, the medium is the interstellar gas and dust within the galaxy. Younger stars, which are more massive and have shorter orbits, experience more dynamical friction than older stars. This causes them to lose energy and settle into more circular orbits over time.
The researchers also found that the rotation speed of a galaxy affects the distribution of stellar orbits. Galaxies with faster rotation speeds tend to have more elliptical stellar orbits, while galaxies with slower rotation speeds have more circular stellar orbits. This is thought to be because the gravitational force that holds a galaxy together is stronger in galaxies with faster rotation speeds, which prevents stars from moving on highly elliptical orbits.
The study provides new insights into the dynamics of galaxies and the role that age plays in shaping the distribution of stars within them. It also has implications for understanding the formation and evolution of galaxies, as the distribution of stellar orbits can be used to infer the past history of a galaxy.
