New research from the Hubble Space Telescope has provided new insights into how the movements of stars are affected by their chemical composition around the core of our galaxy, the so-called "bulge" of the Milky Way.
The observations were presented at the recent American Astronomical Society meeting and focus on Sun-like stars. The information is being used to work out what formation model would more accurately produce the bulge we actually see.
“There are many theories describing the formation of our galaxy and central bulge,” Dr Annalisa Calamida, a member of the Hubble research team, said in a statement. “Some say the bulge formed when the galaxy first formed about 13 billion years ago. In this case, all bulge stars should be old and share a similar motion. But others think the bulge formed later in the galaxy's lifetime, slowly evolving after the first generations of stars were born.
“In this scenario, some of the stars in the bulge might be younger, with their chemical composition enriched in heavier elements expelled from the death of previous generations of stars, and they should show a different motion compared to the older stars. The stars in our study are showing characteristics of both models. Therefore, this analysis can help us in understanding the bulge’s origin.”
In the study, which is submitted for publication, the team discovered that stars richer in heavier elements are moving twice as fast as the chemically poorer star population. They also appear to be in higher concentration closer to the center of the galaxy.
"By analyzing nine years' worth of data in the archive and improving our analysis techniques, we have made a clear, robust detection of the differences in the motion for chemically deficient and chemically enriched Sun-like stars," said lead author Professor WiIl Clarkson from the University of Michigan-Dearborn. "We hope to continue our analysis, which will allow us to make a three-dimensional chart of the rich chemical and dynamical complexity of the populations in the bulge."
The team now wants to look at different areas of the core in order to confirm that the observations are consistent, as well as to better map the movement of the stars. This work is also a great pathfinder project in the preparation of Hubble’s successor, the James Webb Space Telescope, which will be launched next year.