Exploring the Andromeda Galaxy
Among all the galaxies known to us, besides the Milky Way, the Andromeda Galaxy (M31) stands out as one of the most familiar. It is not only the neighbor of the Milky Way but also larger in scale. Visible to the naked eye from Earth, it appears as a bright spot resembling a single star. In reality, that is just its core; its actual diameter is equivalent to that of six full moons. If we could see the Andromeda Galaxy in its entirety, we would realize its significant presence in the night sky.
Scientists have long believed that the Andromeda Galaxy is larger than the Milky Way, roughly double its size. However, on February 5th this year, a team of astronomers from Yunnan University in China calculated the mass of the Andromeda Galaxy to be approximately 1.14 trillion times that of the Sun.
The Andromeda Galaxy is a large spiral galaxy located about 2.56 million light-years away from us. Astronomers estimate its diameter to be over 200,000 light-years, hosting nearly a trillion stars within its expanse.
Calculating the mass of such a colossal galaxy is no easy feat. However, Chinese astronomers utilized astronomical observation tools such as the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to compile the most extensive Andromeda Galaxy celestial bodies catalog with radial velocity measurements worldwide. They successfully plotted the most extensive and accurate rotation curve of the Andromeda Galaxy ever observed. This led to the calculation of the Andromeda Galaxy’s mass at around 1.14 trillion times the mass of the Sun.
In their detailed analysis, the research team gathered data on 13,679 celestial bodies within the Andromeda Galaxy with radial velocity measurements, plotting the rotation curve within 407,600 light-years from its center. The observed data analysis revealed that the rotation curve of the Andromeda Galaxy maintains a nearly constant value of about 220 km per second in its disk, gradually decreasing outward to about 170 km per second at its outer halo.
Based on this information, the research team formulated a mass model of the Andromeda Galaxy involving three components, enabling them to elucidate the distribution of the galaxy’s mass with an accuracy between 5% and 20%. Their calculations revealed the mass of the Andromeda Galaxy to be approximately 1.14 trillion times the mass of the Sun, equivalent to about 1.14 trillion Suns.
The research findings were published online in the Royal Astronomical Society Monthly Notices on February 5th. Professor Chen Bingqiu, one of the co-lead authors from Yunnan University, highlighted that this study introduces a fresh perspective on understanding the mass distribution of the Andromeda Galaxy and spiral galaxies in general, crucial for further comprehension of the dynamical structure and evolution of spiral galaxies.
Previously, scientists widely believed that the Andromeda Galaxy was significantly larger than the Milky Way, with a total mass exceeding that of the Milky Way by over twofold. The mass of its central black hole was estimated to be around 100 million times that of the Sun, whereas the Milky Way’s central black hole’s mass is only about 4.31 million times that of the Sun. However, recent research contradicted this notion. In June of the previous year, Chinese scientists, utilizing observations from the Guo Shoujing Telescope and the APOGEE survey telescope in the United States, precisely measured the Milky Way’s rotation curve and mass. They determined the Milky Way’s mass to be approximately 805 billion times that of the Sun, leading to the conclusion that the Andromeda Galaxy’s mass exceeds that of the Milky Way by only 335 billion solar masses—merely 41.6% larger, not even double as previously thought.
It is essential to note that scientists’ estimations of galaxy masses are based on certain algorithms, resulting in varying values with significant differences.
Source: Reported by “Qilu Evening News” on February 6th, “Chinese Astronomers Calculate Mass of Andromeda Galaxy, About 1.14 Trillion Times that of the Sun”