The National Aeronautics and Space Administration (NASA) recently released a latest cosmic image taken by the Hubble Space Telescope. In the picture, more than 500,000 stars shine in deep space, showing a magnificent landscape of red, white and blue. This image selects the Messier 3 (M3) globular star cluster. As one of the commemorative images for the 250th anniversary of the founding of the United States, it is also one of the largest known globular star clusters in the Milky Way.
Globular star clusters are dense groups of spherical stars that are tightly bound together by gravity. Most of their stars formed almost simultaneously in the same mass of gas, so they are regarded as the oldest group of star populations in the Milky Way. Astronomers have identified about 150 globular star clusters orbiting the Milky Way on the outer edge of the Milky Way. Among them, M3 is particularly eye-catching due to its large scale and special properties.
M3 is not only huge in size, but also in a unique location. It is located far away from the center of the Milky Way and contains more than 240 RR Lyrae variable stars. It is currently the globular star cluster with the largest number of RR Lyrae variable stars known. The brightness of ancient variable stars like RR Lyrae changes periodically in a predictable manner over time. Astronomers can accurately calculate their distance by comparing their intrinsic brightness with the brightness observed on Earth, similar to the standard brightness of car lights at night to determine the distance of a vehicle.
In addition to a rich population of variable stars, about 70 rare "blue straggler" candidates were also identified inside M3. This type of star appears particularly dazzling and bluish in globular star clusters, and looks much "younger" than the surrounding old, reddish stars. Blue outliers were first discovered in M3. The mainstream view is that they accrete matter from nearby stars through the gravitational interaction with companion stars, gain extra mass, and are thus "rejuvenated". They appear to be "rejuvenated" with higher temperatures, bluer colors and stronger brightness, giving them a visual effect that seems to be "rejuvenating".
Scientists generally believe that the unusual properties of M3 may have originated from a star cluster merger event in ancient times. Current observations show that there are two clearly different star populations inside M3, suggesting that it may have been formed by the merger of two globular star clusters. The two star clusters were originally thought to belong to a smaller dwarf galaxy, which was eventually absorbed by the Milky Way during its evolution.
The Hubble Space Telescope has observed M3 many times over the past few decades and recorded it as NGC 5272, providing astronomers with key information for in-depth analysis of the cluster's complex internal structure and unusual star composition. In the latest processed images, blue corresponds to shorter wavelengths in the visible light band, while red corresponds to longer wavelengths and part of the near-infrared band. The colors are assigned according to Hubble's standard image processing process to truly reflect the radiation recorded by the telescope's various filters. Because the color of a star is closely related to its surface temperature, the bluer stars in the picture are hotter, while the redder stars are relatively cooler.
This M3 image is part of Hubble's Treasury program, which aims to systematically observe about half of the known globular star clusters in the Milky Way. By examining these ancient star systems as a whole, astronomers hope to piece together a more complete timeline and reconstruct the historical picture of the formation and evolution of the Milky Way.
After more than thirty years of service, the Hubble Telescope is still one of NASA's flagship observatories. It works in conjunction with the James Webb Space Telescope and the upcoming Nancy Grace Roman Space Telescope to continue to provide humans with a deeper and broader view of the universe and help the scientific community continue to improve its overall understanding of the structure and evolution of the universe.