Antennae Galaxies -A Preview of the Milky Way's Future

The Antennae Galaxies are among the closest known merging galaxies. The two galaxies, also known as NGC 4038 and NGC 4039, began interacting a few hundred million years ago, creating one of the most impressive sights in the night sky. They are considered by scientists as the archetypal merging galaxy system and are used as a standard against which to validate theories about galaxy evolution.

The Antennae Galaxies, located in the constellation of Corvus, the Crow, are named for the two long tails of stars, gas and dust that resemble the antennae of an insect. These "antennae" are a physical result of the collision between the two galaxies, which provides us with a preview of what may happen when our Milky Way galaxy collides with the neighboring Andromeda galaxy in several billion years. Although galaxy mergers today are not common, it is believed that in the past they were an important channel of galaxy evolution.

Andromeda and the Milky Way are approaching one another at a speed of 100 to 140 kilometers per second (62–87 miles/sec). However, this does not mean it will definitely collide with the Milky Way, since the galaxy's tangential velocity is unknown. If they do collide, the two galaxies will likely merge to form a monster elliptical galaxy.

New research on the Antennae Galaxies using the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope shows that this benchmark pair of interacting galaxies is in fact much closer than previously thought - 45 million light-years instead of 65 to 100 million light-years.

An international group of scientists led by Ivo Saviane from the European Southern Observatory has used Hubble's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to observe individual stars spawned by the colossal cosmic collision in the Antennae Galaxies. They reached an interesting and surprising conclusion. By measuring the colors and brightnesses of red giant stars in the system, the scientists found that the Antennae Galaxies are much closer than previously thought: 45 million light-years instead of the previous best estimate of 65 million light-years.

The team targeted a region in the relatively quiescent outer regions in the southern tidal tail, away from the active central regions. This tail consists of material thrown from the main galaxies as they collided. The scientists needed to observe regions with older red giant stars to derive an accurate distance. Red giants are known to reach a standard brightness, which can then be used to infer their distance. The method is known as the tip of the red giant branch (TRGB).

Posted by Casey Kazan. Adapted from a Hubble Space Telescope release.

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