Messier 79

Here’s a wider-field view of Messier 79 (M79). I wanted to capture some of the dark, gray molecular material that shows up from our vantage here on Earth. But there’s much more to the story of M79.

M79 sports a couple of fairly unusual features. Most Milky Way globular clusters are located near the galactic core. M79 is not only distant from the galactic center, from our point of view, it’s on the opposite side of the sky from where we normally see globular clusters. This is because the Earth is between the galactic core and M79.

There’s also some dispute over whether M79 belongs to the Milky Way or whether it’s the property of a nearby dwarf galaxy. And even which dwarf galaxy it might belong to—or might have once belonged to—is a matter of some controversy.

Some scientists believe that it is part of the Canis Major Dwarf Galaxy—a small spheroidal galaxy currently being ripped apart by a close encounter with the Milky Way. But others dispute the very existence of the Canis Major Dwarf Galaxy and posit that it is just a density wave in the Milky Way creating a formation that appears to be a dwarf galaxy. This they call Canis Major overdensity. Yet still others assert that the overdensity is the result of the Milky Way cannibalizing a dwarf galaxy.

To make matters even more confusing, some scientists assert that M79 belonged to a different dwarf galaxy that the Milky Way ripped apart called the Gaia Sausage or Gaia Enceladus. Scientists identified the Gaia Sausage using data from the Gaia Space Telescope, which was tasked with making a detailed map of the Milky Way. They believe the elongated stream of stars came from a head-on collision between the Milky Way and a much smaller galaxy that ripped the small galaxy to shreds.

Globular clusters are ancient collections of stars that are gravitationally bound together in a spheroidal shape. Some are almost as old as the universe itself. They can contain anywhere from tens of thousands of stars to millions of stars. The stars they house tend to be very old as well, because star formation inside the cluster has largely ceased. The formation of globular clusters is not well understood. Current research leans toward the idea that they formed from very dense molecular clouds in the early universe. Some larger globular clusters may once have been dwarf galaxies whose larger star populations were stripped away from the core by larger galaxies.

M79 Facts

Distance: 42,600 light years

Number of stars: 150,000

Diameter: 104 light years

Age: 11.7 billion years