The Euclid team has released a beautiful new image of NGC 6397, one of the closest globular clusters to Earth. NGC 6397, or GCl 74, is located 7,800 light-years away in the southern constellation of Ara. Because of its very dense nucleus, it is known as a core-collapsed cluster. NGC 6397 is 13.4 billion years old and so formed not long after the Big Bang.
Globular clusters are systems of very ancient stars, gravitationally bound into a single structure about 100-200 light-years across.
They contain hundreds of thousands or perhaps a million stars. The large mass in the rich stellar center of a cluster pulls the stars inward to form a ball of stars.
Globular clusters are among the oldest known objects in the Universe and are relics of the first epochs of galaxy formation.
Of the 150 globular clusters belonging to our Milky Way Galaxy, about 70 lie within 13,000 light-years from the Galactic center where their density tends to peak.
“The challenge is that it is typically difficult to observe an entire globular cluster in just one sitting,” Euclid Consortium scientists said.
“Their centers contain lots of stars, so many that the brightest ‘drown out’ the fainter ones.”
“Their outer regions extend a long way out and contain mostly low-mass, faint stars. It is the faint stars that can tell us about previous interactions with the Milky Way.”
“Currently no other telescope than Euclid can observe the entire globular cluster and at the same time distinguish its faint stellar members in the outer regions from other cosmic sources,” added Euclid Consortium scientist Davide Massari, an astronomer at the National Institute for Astrophysics.
“For example, the NASA/ESA Hubble Space Telescope has observed the core of NGC 6397 in detail, but it would take a lot of observing time with Hubble to map the outskirts of the cluster, something Euclid can do in just one hour.”
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