The NASA/ESA Hubble Space Telescope captured this glittering image of the globular cluster NGC 6540 in the Sagittarius constellation. The image was taken with Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys. This is a composite image of an area of the sky that encompasses both instruments’ different fields of view.
Globular clusters are tightly-bound and stable swarms of stars that can hold tens of thousands to millions of stars together. All of the stars are trapped in the closely-packed group by their mutual gravitational attraction. They are usually much larger than open clusters and the strong gravitational attraction between the stars gives them their regular spherical shape, which is why they are named “globular.”
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This sparkling image shows NGC 6540, a globular cluster – a tightly bound swarm of stars that can hold tens of thousands to millions of stars, packed together by their mutual gravitational attraction.
— Hubble (@NASAHubble) August 19, 2022
The brightest stars in this image of NGC 6540 feature prominent cross-shaped patterns of light, or diffraction spikes. Diffraction spikes are image artefacts caused by the structure of Hubble rather than the stars themselves. This phenomenon happens because the path taken by the starlight is slightly disturbed by the internal structure of the telescope, causing bright objects to be surrounded by spikes of light.
Hubble observed NGC 6540 to help astronomers measure the ages, shapes and structures of the globular clusters towards the centre of the Milky Way. Some of the light from these clusters is blocked by the gas and dust surrounding the centre of our galaxy.
The gas and dust also subtly change the colours of the stars. Studying globular clusters can help astronomers understand how our galaxy has evolved since they contain insights into the early history of the Milky Way.
In July, the Hubble Space Telescope captured a similar image of NGC 6569, another globular cluster in the Sagitarrius constellation. That image too was a composite captured using the Wide Field Camera 3 and Advanced Camera for Surveys.