As the United States celebrates Independence Day and the 250th anniversary of the founding of the country, the National Aeronautics and Space Administration (NASA) released a latest image taken by the Hubble Space Telescope. This image is like a red, white, and blue fireworks blooming in the night sky. It not only pays tribute to the long-standing tradition of exploration in the United States, but also shows an ancient star family that is almost as old as the universe.
The star of this image is the globular star cluster NGC 6426 in the outer halo of the Milky Way. Globular star clusters are aggregations of stars tightly bound together by gravity, with an overall approximately spherical distribution. They are regarded as the oldest type of star system in the Milky Way. Currently, astronomers have identified about 150 such ancient star clusters in the Milky Way, which together outline the historical context of the early evolution of the Milky Way.
Unlike general star-forming regions, the stars in globular clusters mostly originate from the same collapsed gas cloud, and therefore are of approximately the same age. The age of NGC 6426 is estimated to be about 13 billion years, which is almost the same as the age of the universe, which is about 13.7 billion years. This makes it one of the oldest globular star clusters in the known Milky Way and a precious window for studying the early stages of the universe.
In this "cosmic fireworks" image, the brilliant colors come from wavelengths of light recorded by the Hubble Telescope through different filters, and then rendered using standard image processing techniques. Blue corresponds to the shorter wavelengths of visible light, while red represents the longer wavelength bands of visible light and some near-infrared light. Because the color of a star is closely related to its surface temperature, blue stars in images are generally hotter, while red stars are relatively cooler. These color differences provide important clues for astronomers to judge the properties of stars.
Astronomers pointed out that the stars in NGC 6426 generally exhibit the characteristics of so-called "low metallicity", that is, they contain relatively few heavy elements except hydrogen and helium. This situation is very similar to the composition of matter in the early universe - during that period, hydrogen and helium dominated, while heavier elements were still in the stage of being gradually produced by nuclear fusion inside massive stars. Because of this, NGC 6426 is regarded as a natural laboratory for studying the environment of the young universe and the formation process of elements.
Researchers also discovered two types of star populations with significantly different chemical properties in the cluster. This evidence shows that after the first generation of massive stars exploded as supernovae, the gas around the cluster was enriched by newly formed heavy elements, and subsequently gave birth to a second generation of stars. Heavy elements ejected by supernova explosions are widely dispersed within star clusters, providing key raw materials for the formation of subsequent stars and even planets. It also confirms the evolutionary picture of "multiple generations of stars" being born one after another in the same globular star cluster.
This image was produced as part of a larger observing program with Hubble. This project focuses on globular star clusters in the outer halo of the Milky Way. By systematically observing these ancient star systems, astronomers hope to determine their ages more accurately and further understand the deep mechanisms of the formation and evolution of the Milky Way. Every "look back" on the history of the Milky Way is constantly improving our understanding of our own cosmic home.
Since entering orbit more than 30 years ago, the Hubble Space Telescope has profoundly changed mankind's understanding of the universe, and its results have been continuously expanded by other NASA observatories, including the James Webb Space Telescope currently in operation. As planned, NASA is about to launch the Nancy Grace Roman Space Telescope at the end of this summer. This new generation of observation platform is expected to continue and expand the scientific legacy of Hubble and Webb, depicting the structure and evolution of the universe with a larger field of view and higher efficiency, thereby giving "ancient fireworks of the universe" like NGC 6426 a new meaning in a broader scientific perspective.