A recent study by MIT physicists has led to an unexpected finding about our galaxy, the Milky Way.
By observing the speed of stars, they’ve discovered that stars further from the galaxy’s center move more slowly than those closer in.
This surprising result could mean the Milky Way’s core has less dark matter than we thought.
This research was based on data from two major astronomical tools: the Gaia space telescope, which tracks over a billion stars in the Milky Way, and APOGEE, a ground-based survey.
Gaia provides detailed information about the position, distance, and motion of stars, while APOGEE offers in-depth data on their properties, such as brightness and temperature.
The team, including Assistant Professor Lina Necib, focused on more than 33,000 stars, some of which are among the farthest in our galaxy.
They calculated each star’s “circular velocity,” the speed at which it orbits the galaxy’s center.
This data helped them create a rotation curve, a graph showing how fast matter rotates at different distances from a galaxy’s center. These curves can tell scientists about the distribution of both visible and dark matter in a galaxy.
Dark matter is a mysterious substance that doesn’t emit light or energy, making it invisible to current scientific instruments. It’s thought to make up a significant portion of the universe’s mass. The concept of dark matter emerged from observations that galaxies, including the Milky Way, rotate in ways that can’t be explained by visible matter alone.
This was first noticed in the 1970s by astronomer Vera Rubin, whose work provided strong evidence for dark matter’s existence.
In this study, the team expected to see a flat curve, indicating a consistent speed of stars across the galaxy, as typically seen in galaxies with a lot of dark matter. However, their findings were surprising. The curve stayed flat up to a certain distance but then showed a significant drop, meaning that stars at the galaxy’s edge were moving slower than expected. This suggests that the gravitational pull from the galaxy’s core, influenced by dark matter, might be weaker than previously thought.
Translating this into a map of dark matter distribution, the researchers concluded that the Milky Way’s core might be lighter and contain less dark matter. This finding is in tension with other measurements and challenges current understanding.
Anna-Christina Eilers, another MIT physicist involved in the study, had previously used Gaia data to chart a flat rotation curve of the Milky Way, suggesting a high density of dark matter. However, the new data, including stars nearly 100,000 light-years from the galaxy’s core, revealed a different picture.
This study opens up new questions about the Milky Way’s structure and the distribution of dark matter. It suggests there might be hidden masses beyond the galaxy’s edge or a need to reconsider the state of equilibrium in our galaxy. The team plans to explore these possibilities in future work, using high-resolution simulations of galaxies similar to the Milky Way.
This unexpected discovery adds a new layer to our understanding of the Milky Way and the mysterious dark matter that shapes it, showing how much more there is to learn about our galaxy and the universe.
