A project of the Dark Energy Survey collaboration


The Ancient Universe, Untouched

Om-Cen Composite

The past can be far, far away, but sometimes it is so close to home. Long ago, the first stars lit up, and hydrogen burned inside them. The hydrogen fused and became helium, which in turn fused into yet heavier elements: through nuclear reactions, the cores of stars birthed all the elements that make up our world. When extremely massive stars with these heavier elements exploded, they sent forth into the universe the stuff that would become new stars, as well as planets, and you and me. These first stars are far away in time and space, but there lives an ancient collection of stars in our galactic backyard that simply grew old slowly and quietly.

Omega Centauri is composed of stars that have elements relatively light in weight—from hydrogen and helium to silicon and neon. However, they are lacking in heavy elements, like iron—the same iron found in our blood and in the steel of our buildings and machines. These stars fused atoms in their cores, but they never grew massive enough to explode, so they just burned on, slowly but surely.

Though Ptolemy cataloged Omega Centauri as a single star 2,000 years ago, it is a dense cluster of several million, very old stars. This globular cluster has been orbiting the Milky Way for 12 billion years, nearly the entire age of the universe. Omega Cen is about 15,000 light-years away from the Galaxy, but just a dozen light-years in diameter itself. What’s more, its millions of stars are separated from each other by just a tenth of a light-year. This is roughly equivalent to a golf ball full of very fine sand sitting at the edge of a football pitch. The nearest star to our solar system is Proxima Centauri, just 4 light-years away—still over 10 times the distance between stars in Omega Cen.

Rediscovered by Edmond Halley (of eponymous cometary fame), Omega Cen (a.k.a., NGC 5139) is a globular cluster located in the direction of the Centaurus constellation. Teeming with millions of ancient furnaces, it is the largest and oldest of the 150 globular clusters orbiting the Milky Way.

Omega Cen is visible with the naked eye and  can appear as large as the full moon.  It lives at Right Ascension, 13 : 26.8 (h:m) and Declination, -47 : 29 (deg:m), should you choose to seek it out yourself.  The image above shows the full cluster in the frame and zoom-in of a small section in the right frame.

Written by: Det. B. Nord [FNAL]
Image Credit: Det.’s M. Murphy and N. Kuropatkin [FNAL]

Comments are closed.