A group of astronomers from Yunnan University, the University of Utah, New Mexico State University and the University of St Andrews have come up with a new way to understand the Milky Way. They studied red giants and used their findings to create a model.
Their research, published in the journal Nature Astronomysuggests that there may be fewer stars in our galaxy than previously thought.
The research team points out that our solar system is located on one of the arms of the Milky Way, far from the center, where a supermassive black hole is thought to exist. This distant position makes it difficult to accurately understand the overall structure of the galaxy.
Moreover, previous estimates of the galaxy’s structure were based on approximations of the number of stars in different regions combined with observations of other galaxies, Phys.org reports.
Predicting the shape and size of the Milky Way
In their new study, the researchers wanted to estimate the number of stars in our galaxy more accurately. They started by performing a detailed census of red giants, and used this data to construct a model that better predicts the shape and size of the Milky Way.
New insights into our galaxy…
“The Milky Way has a more complex radial structure and is larger than previously expected.”
“Our galactic home has just been renovated. Astronomers have peered through the dust and gas that peppers our galaxy and discovered that the core of the Milky Way… photo.twitter.com/NugW8e0gPr— Manuela Casasoli (@manuelacasasoli) July 1, 2024
The team used a variety of techniques to analyze data from the Apache Point Observatory Galactic Evolution Experiment, allowing them to count red giants, which are normally hidden by interstellar dust.
Their refined methods yielded a more accurate count, nearly 250,000, and allowed for more precise positioning of these red giants. This detailed approach provided a clearer understanding of their distribution, particularly within the bulge near the center of our galaxy.
The radius of the galaxy’s half-light beam is twice as large as previously thought
After 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.
According to the researchers, this discovery indicates that the bulge of the galaxy is less dense than previously thought.
One way to determine how extended a galaxy is is to find its half-radius. This is the distance from the center where you can draw a circle that captures half of the galaxy’s total light. For the first time, researchers have directly measured this radius for the Milky Way. They found that it is about twice as large as the best recent models predicted.
“There are many things that need to be rethought,” said co-author Jianhui Lian, an astronomer at Yunnan University in Kunming, China.
For example, it could lower our estimate of the total mass of the Milky Way, he explained. This, in turn, could mean that our galaxy contains more dark matter than we previously thought.