Close encounters between stars in Omega Centauri, the only star cluster visible to the naked eye, leave little room for habitable planets, according to new research. An artist’s conception of exoplanets in a dense star cluster. Image credit: Michael Bachofner. Omega Centauri, also known as NGC 5139, is about 18,000 light-years away, 150 light-years in diameter and 12 billion years old. Of the 200 or so globular clusters that orbit the Milky Way,...