Messier 79

Our Milky Way galaxy may have stripped this globular cluster from another galaxy.

Distance

41,000 light-years

Apparent Magnitude

8.0

constellation

Lepus

object type

Globular Cluster

It's beginning to look a lot like the holiday season in this NASA Hubble Space Telescope image of a blizzard of stars, which resembles a swirling snowstorm in a snow globe. The stars are residents of the globular star cluster Messier 79, or M79, located 41,000 light-years from Earth, in the constellation Lepus. The cluster is also known as NGC 1904. Globular clusters are gravitationally bound groupings of as many as 1 million stars. M79 contains about 150,000 stars packed into an area measuring only 118 light-years across. These giant "star-globes" contain some of the oldest stars in our galaxy, estimated to be 11.7 billion years old. Most globular clusters are grouped around the central hub of our pinwheel-shaped galaxy. However, M79's home is nearly on the opposite side of the sky from the direction of the galactic center. One idea for the cluster's unusual location is that its neighborhood may contain a higher-than-average density of stars, which fueled its formation. Another possibility is that M79 may have formed in an unusual dwarf galaxy that is merging with the Milky Way. In the Hubble image, Sun-like stars appear yellow. The reddish stars are bright giants that represent the final stages of a star's life. Most of the blue stars sprinkled throughout the cluster are aging "helium-burning" stars. These bright blue stars have exhausted their hydrogen fuel and are now fusing helium in their cores. A scattering of fainter blue stars are "blue stragglers." These unusual stars glow in blue light, mimicking the appearance of hot, young stars. Blue stragglers form either by the merger of stars in a binary system or by the collision of two unrelated stars in M79's crowded core. The star cluster was discovered by Pierre Méchain in 1780. Méchain reported the finding to Charles Messier, who included it in his catalog of non-cometary objects. About four years later, using a larger telescope than Messier's, William Herschel resolved the stars in M79, and described it as a "globular star cluster." The image is a combination of observations taken in 1995 and 1997 by Hubble's Wide Field Planetary Camera 2. The red, green, and blue colors used to compose the image represent a natural view of the cluster. The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

NASA, ESA, STScI, F. Ferraro (Universita di Bologna) and S. Djorgovski (California Institute of Technology)

Discovered by Charles Messier’s colleague Pierre Méchain in 1780, M79 is a globular cluster in the constellation Lepus the Hare. Best observed in the month of January, the cluster has an apparent magnitude of about 8. The dense heart of the cluster can be spotted as a small, fuzzy patch in binoculars, but observers will need at least a medium-sized telescope to resolve M79’s individual stars and outer environs.

While most globular clusters in our Milky Way galaxy appear around the galactic core in Sagittarius, M79 is one of the few seen on the opposite side of the sky, away from the galaxy’s center. That’s because Earth lies between M79 and the middle of the galaxy. M79 is about 41,000 light-years from us but roughly 60,000 light-years from the galactic center.

M79 is also one of just two globular clusters in the Messier catalog that our galaxy might have stolen from other nearby galaxies in the not-too-distant past. An unusual density of red giant stars in the direction of the constellation Canis Major (not far from M79) could be the remains of a dwarf galaxy that’s currently being shredded and absorbed by our Milky Way galaxy. M79 might have been snatched from this small galaxy, known as the Canis Major Dwarf Galaxy.

This image of M79 combines visible and ultraviolet observations taken by Hubble in 1995 and 1997. Not surprisingly, the cluster contains many aging red giant stars. However, Hubble has helped show that M79 also includes numerous “blue stragglers,” which are brighter and bluer than astronomers would expect stellar residents of an old globular cluster to be. Astronomers suspect these strange, youthful-looking objects are the products of their compact environments, forming either from stellar mergers or from one star pulling in material from a close neighbor.

For more information on Hubble’s observations of M79, see:

Hubble's Celestial Snow Globe

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Image courtesy of Stellarium

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