An Ancient ‘Metropolis’ Orbiting the Milky Way –One of the Oldest Objects in the Universe


One of 150 globular clusters that orbit the Milky Way, M107, also known as NGC 6171, a compact and ancient family of stars that lies about 21 000 light-years away, is a bustling metropolis: thousands of stars in globular clusters like this one are concentrated into a space that is only about twenty times the distance between our Sun and its nearest stellar neighbour, Alpha Centauri. A significant number of these stars have already evolved into red giants, one of the last stages of a star’s life.

Globular clusters are among the oldest objects in the Universe. And since the stars within a globular cluster formed from the same cloud of interstellar matter at roughly the same time — typically over 10 billion years ago — they are all low-mass stars, as lightweights burn their hydrogen fuel supply much more slowly than stellar behemoths. Globular clusters formed during the earliest stages in the formation of their host galaxies and therefore studying these objects can give significant insights into how galaxies, and their component stars, evolve.

M107 is not visible to the naked eye, but, with an apparent magnitude of about eight, it can easily be observed from a dark site with binoculars or a small telescope. The globular cluster is about 13 arcminutes across, which corresponds to about 80 light-years at its distance, and it is found in the constellation of Ophiuchus, north of the pincers of Scorpius. Roughly half of the Milky Way’s known globular clusters are actually found in the constellations of Sagittarius, Scorpius and Ophiuchus, in the general direction of the centre of the Milky Way. This is because they are all in elongated orbits around the central region and are on average most likely to be seen in this direction.

This stunning new image of Messier 107 at top of page was captured by the Wide Field Imager on the 2.2-metre telescope at ESO’s La Silla Observatory in Chile.

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