The Heart of Omega Centauri

Left: Some 50,000 stars are individually resolved in a Hubble Space Telescope view through the center of the globular cluster Omega Centauri. Click on the image for a low-resolution view, or here for a full-resolution view. Right: The Hubble frame is only 13 light-years wide, but the entire cluster sprawls across some 450 light-years.
Courtesy Adrienne Cool/Hubble Heritage Team/NASA. Ground-based image courtesy Digitized Sky Survey.
Omega Centauri, the biggest and brightest globular star
cluster in the sky, is a beautiful, speckled glow in an amateur telescope.
But no scope on Earth has ever revealed the richness of globular clusters
the way the Hubble Space Telescope has. Astronomy books have long stated
that Omega Centauri contains several million stars, but only when one
gazes into the high-resolution versions of this image does the full
force of that statement come through.

Most of the cluster is made of main-sequence stars roughly
similar to the Sun, though they are much older (about 12 billion years
old compared to the Sun’s 4.6 billion years) and contain only small
traces of elements heavier than hydrogen and helium. This deficiency
of heavy elements is probably why globular-cluster stars seem
not to have planets. Close encounters between stars in this rich
environment may also disrupt any solar systems that do manage to form.
Actual collisions between stars are rare — even in the heart of
a globular, space is mostly very empty — but the cluster is so
old that thousands of collisions have probably occurred. Astronomers
have identified a few post-collision "merged" stars by their odd colors.

This image was assembled from frames taken in ultraviolet,
red, and hydrogen-alpha light. The colors have been balanced to suggest
how the cluster appears to the human eye. Scattered across the swarms
are slightly more massive stars that have evolved to become red giants
(yellow here). The faint blue stars are mostly post-giants fading on
their way to becoming white dwarfs.