A group of astronomers from Yunnan University, the University of Utah, New Mexico State University, and the University of St Andrews have devised a new way of understanding the Milky Way galaxy. They studied red giants and used their findings to create a model.
Their research, published in the journal Nature Astronomy, suggests there might be fewer stars in our galaxy than previously believed.
The research team points out that our solar system is located on one of the Milky Way galaxy’s arms far from its center, where a supermassive black hole is believed to exist. This distant position makes it challenging to accurately understand the galaxy’s overall structure.
Moreover, previous estimates of the galaxy’s structure relied on approximations of star numbers in different areas combined with observations of other galaxies, as reported by Phys.org.
Predicting the shape and size of the Milky Way galaxy
In their new study, the researchers aimed to more accurately estimate the amount of stars in our galaxy. They began by conducting a detailed census of red giants, using this data to construct a model that better predicts the shape and size of the Milky Way
New insights on our galaxy…
"The Milky Way has a more complex radial structure and larger size than previously expected."
"Our Galactic home just got a remodel. Peering through the dust and gas that intersperse our Galaxy, astronomers have found that the Milky Way’s core is… pic.twitter.com/NugW8e0gPr— Manuela Casasoli (@manuelacasasoli) July 1, 2024
The team employed various techniques to analyze data from the Apache Point Observatory Galactic Evolution Experiment. This enabled them to count red giants, which are typically hidden by interstellar dust.
Their refined methods provided a more precise count, nearing 250,000, and allowed for more accurate positioning of these red giants. This detailed approach provided clearer insight into their distribution, especially within the bulge near the center of our galaxy.
Galaxy’s half-light radius is twice as large as previously thought
Upon integrating the data into their model, the research team observed that the density of red giants stabilizes around the midpoint between the galaxy’s edges and its bulge. This contrasts with previous models that suggested an exponential increase in density.
The researchers said this discovery indicates the bulge of the galaxy is less dense than previously believed.
One way to determine how expansive a galaxy is involves finding its half-light radius. This is the distance from its center where you can draw a circle that captures half of the galaxy’s total light. For the first time, researchers directly measured this radius for the Milky Way. They discovered it is about twice as large as what the best latest models predicted.
“There are a lot of things that need to be revisited,” says co-author Jianhui Lian, an astronomer at Yunnan University in Kunming, China.
For example, it could reduce our estimate of the total mass of the Milky Way, he explained. This, in turn, might mean our galaxy contains more dark matter than we previously believed.
