Red, white, and blue stars light up a new image from NASA's Hubble Space Telescope, released on July 4 to mark the United States' 250th anniversary. The target is globular cluster NGC 6426, a spherical collection of ancient stars sitting in the outer halo of the Milky Way galaxy.
At approximately 13 billion years old, NGC 6426 is one of the oldest known globular clusters in the galaxy and is almost as old as the universe itself, which formed roughly 13.7 billion years ago. It is one of about 150 known globular clusters in the Milky Way. Stars in these clusters are thought to form together from the same collapsing cloud of gas, which means they tend to share similar ages.
The colors in the image carry scientific meaning. Blue indicates shorter wavelengths of visible light, while red depicts longer wavelengths of visible light and some near-infrared light. Because color and temperature in stars are directly related, the blue stars in the image are hotter and the red stars are cooler.
The stars of NGC 6426 have low metallicity, meaning they contain fewer elements heavier than hydrogen and helium. Those conditions resemble those of the early universe, before heavier elements began forming through nuclear fusion inside massive stars. Massive stars that explode as supernovae fling those heavier elements into surrounding space, seeding the universe with materials that can eventually build new stars and planets.
Researchers have found evidence for two chemically distinct populations of stars inside the cluster. The slightly younger and more metallic population appears to have been enriched by material from the explosive deaths of the cluster's earlier stars, suggesting a layered history of stellar generations within the same structure.
Hubble captured this image as part of a broader study of globular clusters in the Milky Way's halo. The goal of that study is to determine the ages of those clusters and learn more about how the galaxy formed and evolved over time. Over three decades in orbit, Hubble has produced discoveries that other NASA missions continue to build on, including the infrared-detecting James Webb Space Telescope. The Nancy Grace Roman Space Telescope, which will complement both, is scheduled to launch in late summer.
