Globular clusters are densely packed, spherical collections of several hundred thousand stars. They are among the oldest known objects in the Universe and are relics of the first epochs of galaxy formation. A stunning new image from the NASA/ESA Hubble Space Telescope shows one of these objects, NGC 1866.
This Hubble image shows NGC 1866, a massive globular cluster located in the constellation Dorado, some 160,000 light-years away. The image was made from separate exposures taken in the visible region of the spectrum with Hubble’s Wide Field Camera 3 (WFC3). Five filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble.
NGC 1866 is found at the very edges of a Milky Way satellite galaxy called the Large Magellanic Cloud, which is approximately 160,000 light-years away from Earth.
Also known as ESO 85-52 and LW 163, the cluster was discovered in 1826 by the Scottish astronomer James Dunlop.
NGC 1866 is a surprisingly young globular cluster situated close enough to us that its stars can be studied individually — no mean feat given the mammoth distances involved in studying the cosmos.
There is still debate over how globular clusters form, but observations such as this have revealed that most of their stars are old and have a low metallicity.
In astronomy, ‘metals’ are any elements other than hydrogen and helium; since stars form heavier elements within their core as they carry out nuclear fusion throughout their lifetimes, a low metallicity indicates that a star is very old, as the material from which it formed was not enriched with many heavy elements.
It’s possible that the stars within globular clusters are so old that they were actually some of the very first to form after the Big Bang.
In the case of NGC 1866, though, not all stars are the same — different populations, or generations, of stars co-exist within the cluster.
Once the first generation of stars formed, the cluster may have encountered a giant gas cloud that sparked a new wave of star formation and gave rise to a second, younger, generation of stars — explaining why it seems surprisingly youthful.
