When we think of the Milky Way, we often see a vast array of stars stretching across the night sky that have inspired countless generations to contemplate the vastness of the universe. According to NASA, the diameter of the Milky Way Galaxy is about 100,000 light-years. However, this number is just an approximation, and according to the latest research, our galaxy may be much larger than previously thought – perhaps ten times larger. This uncertainty stems from the challenges astronomers face when examining a galaxy from the inside out.
the Milky Way system Studying it is inherently difficult because we are in it. Unlike other galaxies that can be seen from an outside perspective, the Milky Way surrounds us. This inward perspective means that various components of the galaxy, such as gas, dust and stars, obstruct our view. In addition, our solar system is located in a relatively suburban part of the galaxy, making it difficult to observe its edges without disturbing the denser regions. SciShow.
Draw a map of the Milky Way
Over the centuries, scientists have made great strides in mapping our galaxy. To determine the size of the Milky Way, astronomers first had to determine its boundaries. Just as Earth's atmosphere gradually fades into space, the edges of the Milky Way are also fading away without a clear endpoint in intergalactic space. So, scientists have to set an arbitrary threshold for where the galaxy ends.
One way is to study gravitational interactions with nearby galaxies. According to a 2020 study, for example, based on such an interaction, the diameter of the Milky Way Galaxy could reach 1.9 million light-years. However, a more common approach uses the concept of “viral radius”, which is the distance from the galactic center where the density of matter drops below a certain value. By doubling this radius, astronomers estimate the diameter of the galaxy.
The role of dark matter
Although the visible portion of the Milky Way is only about 200,000 light-years across, the galaxy is much larger when its dark matter halo is taken into account. Dark matter, which makes up much of the galaxy's mass, does not condense into the spiral structure familiar to visible matter. Instead, they form a spherical halo extending around the galaxy. The gravitational influence of the dark matter halo affects the motion of stars in the Milky Way, allowing astronomers to estimate the size and mass of the galaxy.
The latest discoveries and the Gaia space telescope
The latest data from the Gaia Space Telescope has revolutionized understanding of its size. Gaia's precise measurements of distances and star motions have provided new insights into the structure of the galaxy. According to Gaia's 2022 update, the galaxy's total mass is about 200 billion times the mass of the Sun, which is much lower than previous estimates of 1 trillion solar masses. This discrepancy calls previous models into question and suggests that the Milky Way's dark matter halo may be less massive than previously thought.
However, this low mass estimate also raises questions about the ratio of dark matter to regular matter in the Milky Way. Similar galaxies typically show a ratio of about 10:1, while according to the new data, this ratio is only 2.3:1. This could mean that the distribution of dark matter in our galaxy is unique, or that the stars chosen by Gaia do not represent the entire halo.
The future of Milky Way research
While astronomers await more data from Gaia and the upcoming Rubin Observatory, the true size of the Milky Way remains uncertain. If the Gaia results are correct, it could be up to 800,000 light-years across, a big change from the traditional 100,000 light-years. This amendment reflects the dynamic and evolving nature of astronomical research, emphasizing the importance of continuous observation and technological advances.
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