New images from NASA’s Hubble Space Telescope show twinkling red, white and blue stars that look like sparklers in the night sky. NASA released this image to commemorate the United States’ 250th anniversary, celebrating America’s long history of exploration while showcasing one of the oldest collections of stars in the galaxy.
Beyond its patriotic appearance, this image provides an unusual look at a star system that has survived through nearly the entire history of the universe.
Star cluster 13 billion years ago
The object of interest is NGC 6426, a globular cluster located in the outer halo of the Milky Way. A globular cluster is a group of dense, spherical stars that remain bound together by gravity. Approximately 150 of these ancient star clusters are known to exist within our galaxy.
Most of the stars in a globular cluster are born from the same collapsing gas cloud, so they tend to be about the same age. NGC 6426 is estimated to be about 13 billion years old, making it one of the oldest globular clusters in the Milky Way. The universe itself is about 13.7 billion years old, so this star cluster formed shortly after the universe was born.
This unusual age makes NGC 6426 a valuable record of conditions in the early Universe.
Meaning of colors in Hubble images
Bright colors aren’t just for visual appeal. These represent different wavelengths of light collected through Hubble’s filters and processed using standard scientific techniques.
Blue emphasizes short wavelengths of visible light, while red represents longer wavelengths of visible light and some near-infrared light. A star’s color is closely related to its temperature, so blue stars are hotter and red stars are cooler.
Ancient stars reveal the early universe
NGC 6426 stars have what astronomers call “low metallicity,” meaning they contain relatively small amounts of elements heavier than hydrogen or helium. This chemical composition is very similar to that of the young Universe, where matter consists almost entirely of hydrogen and helium, and heavier elements are just beginning to form inside massive stars through nuclear fusion.
Scientists also found evidence that the cluster contains two chemically distinct populations of stars. The discovery suggests that slightly younger stars formed after an earlier generation of massive stars ended their lives in powerful supernova explosions.
These explosions scattered newly produced heavy elements throughout the cluster, concentrating the gas that would later give birth to another generation of stars. The same process gradually filled the universe with the ingredients needed to form planets and many of the elements found throughout the universe today.
Hubble continues to unravel the history of the Milky Way
NASA captured this image as part of its ongoing study of globular star clusters in the Milky Way’s halo. By measuring the age of galaxies and studying their chemical composition, astronomers hope to better understand how our galaxy formed and evolved over billions of years.
For more than 30 years, the Hubble Space Telescope has changed the way we view the universe through groundbreaking discoveries. Now, those observations are complemented by NASA’s James Webb Space Telescope, which studies the universe in infrared light, and the Nancy Grace Roman Space Telescope, scheduled to launch in late summer, is expected to further expand our understanding of the universe.
