Astronomers have discovered that our home galaxy may be larger than we first thought.
A new model of the Milky Way revealed that our galaxy is wider than we thought, according to a new paper in the journal Astronomy of nature.
Scientists have discovered that the bulge at the center of our galaxy is less densely packed with stars than expected.
NASA
“…we obtained a significantly larger ‘size’ (defined as the radius of the light radius) for the Milky Way than expected,” the researchers wrote in the paper.
The Milky Way is a barred spiral galaxy with a central barred structure and several spiral arms extending from the center. The galaxy has a dense central bulge around the galactic center, which is thought to contain a supermassive black hole called Sagittarius A*. The Milky Way contains between 100 billion and 400 billion stars, but the exact number is difficult to determine due to the galaxy’s enormous size and the presence of dust that obscures our view.
“Our understanding of the structure of the Milky Way has improved tremendously in recent decades due to advances in galactic observations. Due to the proximity of our home galaxy, we are able to study substructures of the Milky Way (such as disc heights, spiral arms and bar/X-shape) in great detail, but from the same for this reason, the global picture of the galactic structure is still incomplete,” the researchers wrote in the article.
“The position of the Sun embedded in the disk results in high-visibility extinction towards the densest region in the galaxy, making data collection from large samples of stars over a wide spatial extent expensive in terms of observation time. For example, the radial surface brightness profile across the galaxy, a fundamental observable of galaxies, which contains rich information about their assembly history and is easily obtained from their images, has long been missing from the Milky Way.”
In the paper, scientists describe how they measured the brightness of all parts of our galaxy and took a census of the red giants scattered throughout the Milky Way. They found that the bulge at the center of the galaxy is not as densely packed as first thought, and is also flatter; The Milky Way thus has a larger half-light radius than we knew.
The half-light radius is a measure used in astronomy to describe the size of an astronomical object, defined as the radius at which half the total light (or luminosity) of the object is emitted. In other words, it is the distance from the center of the object to the point where half of the total light from the object is contained in a sphere of that radius.
NASA
“As the profile of the inner disc flattens, the radius of the Milky Way radius is significantly larger than expected from a picture of the Milky Way structure with a bulge and single-exponential thick and thin disc components,” they wrote.
“We also confirm that the Milky Way’s size history is broadly consistent with high-redshift galaxies, but with systematically smaller sizes. Our results suggest that the Milky Way has a more complex radial structure and larger size than previously expected.”
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