In this week's image from the Hubble Space Telescope, the sky is filled with stars. There is an enormous collection of tens of thousands or even millions of stars tightly bound by gravity and densely packed together.

The constellation of Sagittarius is home to this particular cluster. Two of Hubble's instruments, the Wide Field Camera 3 and the Advanced Camera for Surveys, operate mostly in the visible light wavelength.

This star-studded image from the NASA/ESA Hubble Space Telescope shows the heart of the globular cluster NGC 6638 in the constellation Sagittarius. The star-strewn observation highlights the density of stars at the heart of globular clusters, which are stable, tightly bound clusters of tens of thousands to millions of stars. To capture the data in this image, Hubble used two of its cutting-edge astronomical instruments: Wide Field Camera 3 and the Advanced Camera for Surveys.
The heart of the globular cluster NGC 6638 in the constellation Sagittarius. ESA/Hubble & NASA, R. Cohen

Before Hubble was launched, it was hard to study these objects because they required high-resolution images with little interference.

It is almost impossible to distinguish the stars in a cluster with a ground-based telescope. It is not possible to tell a star from another from Hubble's location in Earth's atmosphere. Hubble has been used to study how stars evolve and how gravity affects them.

One such cluster called Messier 92 is the target of an early science program and will soon be studied with another tool. The project will look at star-forming regions using instruments that look in theIR rather than visible light.

The team is working on special software to resolve individual stars within a densely packed area, according to the leader of the team.

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