A stunning image taken by the Hubble Space Telescope shows the chaotic and densely packed stars of the globular cluster NGC 6355.
The globular cluster is located about 31,000 light-years from Earth in the inner region of the Milky Way—so deep in our galaxy that it is only 4,600 light-years from our galaxy’s central supermassive black hole, Sagittarius A*.
Globular clusters like this one contain tens of thousands to millions of stars tightly bound together by mutual gravitational attraction. These dense stellar populations give globular clusters a roughly spherical shape.
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The globular cluster NGC 6355, located in the inner part of the Milky Way, is densely filled with tens of thousands or millions of stars. (Image credit: ESA/Hubble and NASA, E. Noyola, R. Cohen)
Globular clusters are found in galaxies of all shapes and sizes and tend to be the oldest structures in their home galaxies. They are filled with older, redder stars than in open star clusters, which are smaller than globular clusters.
This image of NGC 6355, using data from the Hubble Space Telescope’s Advanced Camera for Surveys and Wide Field Camera 3, captures stunning details of the dense and bright stellar heart at the center of the globular cluster. Agency (ESA), mission partner. A rarer scattering of stars on the outskirts of the globular cluster is also visible with crystal clarity.
The central red and blue stars of NGC 6355 can be clearly seen in this image, showing the tremendous observational power of Hubble, which has revolutionized the study of globular clusters. Hubble is able to capture these amazing views because it is located about 330 miles (530 kilometers) above the surface of our planet. This vantage point frees the telescope from the distorting effects of the Earth’s atmosphere, which makes it nearly impossible for ground-based telescopes to distinguish between individual stars in globular clusters.
Hubble’s observations have yielded a wealth of information about globular clusters.
In 2006, the telescope made the first direct observations of white dwarfs — dim stellar remnants that form when stars with masses similar to the Sun run out of fusion fuel and undergo gravitational collapse — in globular star clusters. These observations have helped astronomers better understand the age and origin of stars in globular clusters, as well as the evolution of these clusters.
In 2021, Hubble observations allowed astronomers to make the first measurement of black holes in the core-collapsed globular cluster NGC 6397. They expected to find an intermediate-mass black hole at the center of this globular cluster, but instead found a concentration of smaller black holes in NGC 6397, located about 7,800 light-years from Earth.
Hubble also took pictures of Messier 15, which is about 12 billion years old and is the oldest known globular cluster.
You can see more Hubble images of globular clusters on the ESA website.
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