Say, “M9,” to a soldier, and he’ll think of a Beretta pistol. Say, “M9,” to an astronomer and he’ll think of this star cluster. Charles Messier described the 9th entry in his astronomical catalog as “Nebula, without star, in the right leg of Ophiuchus …”. But Messier 9 (M9) does have stars; it’s known to modern astronomers as a globular cluster of over 300,000 stars within a diameter of only about 90 light-years. It lies some 25,000 light-years distant, near the central bulge of our Milky Way galaxy. This Hubble Space Telescope close-up resolves the dense swarm of stars across the cluster’s central 25 light-years. The stars are at least twice the age of the Sun and deficient in heavy elements. The stars’ colors correspond to their temperatures. Redder stars are cooler, bluer stars are hotter. Many of the cluster’s cool red giant stars show a yellowish tint in this sharp Hubble view.
NGC 3201 is an oddball among the 150-or-so globular star clusters in the Milky Way. It is moving very rapidly through the galaxy, and its motion is retrograde, that is, it’s orbiting around the galactic core in the opposite direction of most of the stars in the galaxy. That’s led to speculation that it may have come from outside and have been captured.
Also, it contains a black hole which was revealed by the strange movements of a star being quickly flung around the massive, invisible singularity.
M9 is one of the globular clusters closest to the center of the Milky Way Galaxy, only around 5,500 light-years from the galactic core. It’s about 25,800 light-years from Earth.
M9 has an apparent magnitude of 7.9, an angular size of 9.3′, and can be viewed with a small telescope. It is one of the nearer globular clusters to the center of the galaxy as is around 5,500 light-years from the Galactic Core. Its distance from Earth is 25,800 light-years.
The total luminosity of this cluster is around 120,000 times that of the Sun. It has an apparent magnitude of 7.9, so it can be viewed with a small telescope.
This tight grouping of thousands of stars is located near the edge of the Large Magellanic Cloud, a satellite galaxy of our own Milky Way. The stars orbit closely to one another, like bees swarming around a hive. In the dense center of one of these clusters, stars are 100 to 1,000 times closer together than the nearest stars are to our Sun, making planetary systems around them unlikely.
Usually, globular clusters contain stars that are born at the same time. NGC 1805 is unusual because it contains two different populations of stars with ages millions of years apart. Observing such clusters of stars can provide data on how stars evolve and on what factors determine whether they end their lives as white dwarfs or explode as supernovae.
The Advanced Camera for Surveys on board the Hubble Space Telescope took this picture of the globular cluster NGC 1783. This is one of the biggest globular clusters in the Large Magellanic Cloud, a satellite galaxy of our galaxy.
NGC 6441 is a globular star cluster about 13,000 light years from Earth. It is estimated that the cluster’s stars have 1.6 million times the mass of the Sun, making it one of the most massive and luminous globular clusters in the Milky Way.
Messier 5 (M5) is a globular star cluster of 100,000 or more stars bound by gravity into a region around 165 light-years in diameter. It’s about 25,000 light-years away. M5 is one of the oldest globulars in our galaxy, with stars estimated to be nearly 13 billion years old. The beautiful star cluster is a popular target for Earthbound telescopes. This closeup that spans about 20 light-years near the central region of M5 was taken by the Hubble Space Telescope. The cluster’s aging red and blue giant stars and rejuvenated blue stragglers stand out in yellow and blue hues.
M80 is in the constellation Scorpius between the stars α Scorpii (Antares) and β Scorpii in a part of the Milky Way rich in nebulae. When viewed with a modest amateur telescope (like mine), it appears as a mottled ball of light. This Hubble image shows more detail. M80 is roughly 95 light-years in diameter. It contains several hundred thousand stars, making it one of the more densely populated globular clusters in the galaxy.
M80 contains a fair number of blue stragglers, stars that appear to be much younger than the cluster itself. Astronomers believe that these stars lost part of their outer layers during close encounters with other cluster members or as the result of collisions between stars in the tightly packed cluster. Images from Hubble show regions with very high blue straggler densities which suggests that the center of the cluster probably has a very high capture and collision rate.
This is NGC 6535, a globular cluster 22,000 light-years away in the constellation of Serpens (The Serpent). It’s about one light-year across.
Globular clusters are tightly bound groups of stars which orbit galaxies. The Latin word globulus, from which these clusters take their name, means a small sphere. A large mass in the rich stellar centre of a globular cluster pulls the stars inward to form a ball of stars.
Globular clusters are generally very ancient objects that form around the same time as their host galaxy. Thus far, no new star formation has been observed within any globular cluster. The lack of young stars explains the abundance of aging yellow stars in this image, most of them containing very few heavy elements.
This is an image of the core fo the globular star cluster Messier 69. It is made up of visible light and infrared data taken by the Hubble Space Telescope. The cluster was discovered by Charles Messier in 1780. It’s located 29,700 light-years from Earth in the constellation Sagittarius. It’s too dim to be seen with the naked eye, but it can be viewed with a pair of binoculars, especially during August.
The stars in M69 have over ten times more iron than stars in other globular clusters of the same age. Iron is the heaviest element created by fusion in a star unless it explodes as a supernova.
Messier 2 or M2 (aka NGC 7089) is a globular cluster in the constellation Aquarius. It’s one of the larger globular clusters known—rich, compact, and significantly elliptical—containing over 150,000 stars. It’s one of the oldest globulars in our galaxy, around 13 billion years old. This Hubble image shows the core of the cluster.
Image Credits: NASA, ESA, STScI, and A. Sarajedini (University of Florida)
Messier 70 (aka M70 or NGC 6681) is a globular cluster of stars in the southern constellation of Sagittarius. It’s about 29,400 light-years away from Earth and roughly 6,500 light-years from the Galactic Center. M70 has undergone core collapse, so it has a very small core radius of 0.22 light-years.
Messier 62 is located relatively close to the galactic center, so tidal forces likely are responsible for its being one of the most irregularly shaped globular clusters. The core of M62 (toward the upper right in this Hubble image) contains around 150,000 stars and its very own stellar mass black hole.