As part of Hubble’s 35th anniversary celebrations, astronomers have obtained a stunning new image of a rich collection of scattered stars called Messier 72.
This Hubble image shows Messier 72, a globular cluster some 50,000 light-years away in the constellation of Aquarius. Image credit: NASA / ESA / Hubble / A. Sarajedini / G. Piotto / M. Libralato.
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.
It is thought that every galaxy has a population of globular clusters. Our Milky Way Galaxy hosts at least 150 such objects and a few more are likely to exist hidden behind the Galaxy’s thick disk.
Messier 72 is located approximately 50,000 light-years away from Earth in the constellation of Aquarius.
Also known as M72 or NGC 6981, this globular cluster is nearly 9.5 billion years old.
It has an apparent magnitude of 9.4 and appears as a faint patch of light in small telescopes. The best time to observe it is during September.
Messier 72 was first discovered in 1780 by Pierre Méchain, a French astronomer and colleague of Charles Messier.
It was the first of five star clusters that Méchain would discover while assisting Messier and is one of the most remote clusters in Messier’s catalog.
“Messier 72 is a particularly special target because it was the first image ever published in the Hubble Picture of the Week series, on April 22, 2010,” Hubble astronomers said in a statement.
“For fifteen years, our team has been publishing a new Hubble image every Monday for everyone to enjoy.”
“This has resulted in nearly 800 images being added to the vast Hubble image archive over the years.”
“The striking variety in the color of the stars in the new image of Messier 72, particularly compared to the original image, results from adding ultraviolet observations to the previous visible-light data,” they added.
“The colors indicate groups of different types of stars.”
“Blue stars are those in the cluster that were originally more massive, and have now reached hotter temperatures after burning through much of their hydrogen fuel; the bright red objects are lower-mass stars that have now become red giants.”
“Studying these different groups help us to understand how globular clusters, and the galaxies they were born in, initially formed.”
