Monday Bites: Packed Together

 Monday Bites: Packed Together 

Credit: ESO

On average, the distance between any two stars in our Milky Way galaxy is roughly five light-years. Our Sun's nearest neighbor, Proxima Centauri, sits 4.25 light-years away. Its binary pair, Alpha Centauri, is a hair's breadth away at 4.35 light-years. Barnard's star, a big name, lives two blocks down at 5.96 light-years, looking into the direction of the constellation of Ophiuchus. Extending the stellar ladder, the farthest star we can see in the night sky, Deneb, in the summer triangle asterism over the northern (hemisphere) skies, is over 2,600 light-years distant. 

Instead of being farther out, what if the stars huddled close together, perhaps less than a light year apart, packed so densely that from a distance, a conglomerate hundred million of them give the appearance of a comet's diffuse head? Welcome, ladies and gentlemen to the magnificent globular clusters. 

A globular cluster is almost like a galaxy, bringing together tens of thousands to upwards of ten million stars bound into a spheroidal globule through their mutual gravity. A typical globular cluster or globular can occupy a volume of 300 light-years with more than a thousand stars concentrated in cubic-light year volume at the core of the globular. Globular clusters are where the oldest stars in the known universe, the so-called Population II stars or the mommies and daddies of the present generation of Sun-like stars, gather for council. The popular belief among astronomers is that the individual stars in globulars must've formed simultaneously from a single molecular could complex, albeit a giant one, collapsing at various places. However, the variety of stars seen in the globulars challenges that view and hints at something else. Since globulars aren't usually found in the galactic plane but are extensively distributed in a halo around the galactic center, astronomers suspect them to be the key pieces that might explain the origin and subsequent evolution of galaxies. 

What you see here is the largest globular cluster known so far in the Milky Way, Omega Centauri. The Omega Centauri globular (catalog number NGC 5139 or Caldwell 80) lies far away at 17,000 light-years plus in the direction of the constellation of Centaurus. Weighing over 4 million times that of our Sun, Omega Centauri packs 10 million individual stars and stretches over 150 light-years.