NGC 6397

Euclid’s view of globular cluster NGC 6397 ESA25170813.jpg
(c) ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi, CC BY-SA IGO 3.0
This sparkly image shows Euclid’s view on a globular cluster called NGC 6397. Globular clusters are collections of hundreds of thousands of stars held together by gravity.
Located about 7800 light-years from Earth, NGC 6397 is the second-closest globular cluster to us. Together with other globular clusters it orbits in the disc of the Milky Way, where the majority of stars are located.
Globular clusters are some of the oldest objects in the Universe. That’s why they contain a lot of clues about the history and evolution of their host galaxies, like this one for the Milky Way.
The challenge is that it is typically difficult to observe an entire globular cluster in just one sitting. Their centres 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.
Read more about Euclid’s view of globular cluster NGC 6397
Explore this image at the highest resolution in ESASky
Read more about Euclid's first images
[Technical details: The data in this image were taken in just five hours of observation. This colour image was obtained by combining VIS data and NISP photometry in Y and H bands; its size is 8800 x 8800 pixels. VIS and NISP enable observing astronomical sources in four different wavelength ranges. Aesthetics choices led to the selection of three out of these four bands to be cast onto the traditional Red-Green-Blue colour channels used to represent images on our digital screens (RGB). The blue, green, red channels capture the Universe seen by Euclid around the wavelength 0.7, 1.1, and 1.7 micron respectively. This gives Euclid a distinctive colour palette: hot stars have a white-blue hue, excited hydrogen gas appears in the blue channel, and regions rich in dust and molecular gas have a clear red hue. Distant redshifted background galaxies appear very red. In the image, the stars have six prominent spikes due to how light interacts with the optical system of the telescope in the process of diffraction. Another signature of Euclid special optics is the presence of a few, very faint and small round regions of a fuzzy blue colour. These are normal artefacts of complex optical systems, so-called ‘optical ghost’; easily identifiable during data analysis, they do not cause any problem for the science goals. ]
[Image description: This square astronomical image is speckled with hundreds of thousands of stars visible across the black expanse of space. The stars vary in size and colour, from blue to white to yellow/red. Blue stars are younger and red stars are older. More stars are located at the centre of the image, where they are bound together by gravity into a spheroid conglomeration – also called a globular cluster. Some of the stars are a bit larger than the rest, with six diffraction spikes.]

NGC 6397 (ESO).jpg
Autor/Urheber: European Southern Observatory, Lizenz: CC BY-SA 3.0
The globular cluster NGC 6397, located at a distance of approx. 7,200 light-years in the southern constellation Ara. It has undergone a "core collapse" and the central area is very dense. It contains about 400,000 stars and its age (based on evolutionary models) is 13,400 ± 800 million years. The photo is a composite of exposures in the B-, V- and I-bands obtained in the frame of the Pilot Stellar Survey with the Wide-Field-Imager (WFI) camera at the 2.2-m ESO/MPI telescope at the ESO La Silla Observatory. It was prepared and provided by the ESO Imaging Survey team. The spikes seen at some of the brighter stars are caused by the effect of overexposure (CCD "bleeding").

Colours & filters
Band Telescope
Optical B MPG/ESO 2.2-metre telescope WFI
Optical V MPG/ESO 2.2-metre telescope WFI

Optical I MPG/ESO 2.2-metre telescope WFI

Hubble's view of dazzling globular cluster NGC 6397.jpg
(c) ESA/Hubble, CC BY 4.0
This ancient stellar jewelry box, a globular cluster called NGC 6397, glitters with the light from hundreds of thousands of stars.

Astronomers used the NASA/ESA Hubble Space Telescope to gauge the distance to this brilliant stellar grouping, obtaining the first precise measurement ever made to an ancient globular cluster.

The new measurement sets the cluster’s distance at 7800 light-years away, with just a 3 percent margin of error. NGC 6397 is one of the closest globular clusters to Earth.

By measuring an accurate distance to NGC 6397, astronomers then calculated a precise age for the cluster. The cluster is 13.4 billion years old, which means it was born shortly after the Big Bang. NGC 6397 is one of about 150 globular clusters that orbit outside of our Milky Way galaxy’s comparatively younger starry disc. These spherical, densely packed swarms of hundreds of thousands of stars are our galaxy’s first homesteaders.

The cluster’s blue stars are near the end of their lives. These stars have used up their hydrogen fuel that makes them shine. Now they are converting helium to energy in their cores, which fuses at a higher temperature and appears blue.

The reddish glow is from red giant stars that have consumed their hydrogen fuel and have expanded in size.

The myriad small white objects include stars like our Sun.

This image is composed of a series of observations taken from July 2004 to June 2005 with Hubble’s Advanced Camera for Surveys. The research team used Hubble’s Wide Field Camera 3 to measure the distance to the cluster.

Caldwell Catalogue.jpg
Autor/Urheber: Roberto Mura, Lizenz: CC BY-SA 3.0
Caldwell Catalogue objects.

NGC6397.jpg
NGC 6397 globular cluster