For the first time, astronomers have mapped the 3D motions of stars in another galaxy, an incredible accomplishment that could tell us a whole lot more about how galaxies formed in the universe.
The study was led by the Kapteyn Astronomical Institute and Leiden Observatory, both in the Netherlands. They used data from the NASA/ESA Hubble Telescope and ESA’s Gaia observatory to measure the motion of stars in the Sculptor Dwarf Galaxy, a satellite galaxy of the Milky Way 260,000 light-years from us that contains hundreds of thousands of stars. In this study, they were able to track the motion of ten.
“To give you an idea on how precise our measurement is, the apparent motion of Sculptor corresponds to the apparent motion that a person would have when walking at a distance of one light-year!” Davide Massari, lead author of the study, told IFLScience.
The data from Hubble and Gaia was produced 12 years apart, but allowed scientists to measure the exact 3D motion of stars in the Sculptor galaxy. They found that stars move on elongated radial orbits, meaning they spiral out from the center of the galaxy.
Sculptor is known as a dwarf spheroid galaxy and is thought to be one of the most dark matter-dominated objects in the universe. This means it’s an ideal target for studying dark matter and working out how it's distributed in galaxies.
“The 3D motions that we measured for stars in the Sculptor dwarf galaxy are consistent with the predictions of the Lambda Cold Dark Matter scenario, which is one of the models that tries to explain how all the galaxies in the universe formed and evolved to their current shape,” said Massari. “This in turn strongly support the existence of dark matter.”
Looking at the positions of the stars, the astronomers were able to discern that dark matter is concentrated towards the center of the galaxy, which aligns with our current cosmological models.
The study as a whole also gave us a better handle on how this galaxy is moving with respect to us. The findings showed it is on an elongated orbit around our galaxy, taking it as far as 725,000 light-years away, much further than thought. It’s currently at its closest point to us, though.