Poster Version
A cluster brimming with millions of stars glistens like an iridescent opal
in this image from NASA's Spitzer Space Telescope. Called Omega Centauri,
the sparkling orb of stars is like a miniature galaxy. It is the biggest
and brightest of the 150 or so similar objects, called globular clusters,
that orbit around the outside of our Milky Way galaxy. Stargazers at
southern latitudes can spot the stellar gem with the naked eye in the
constellation Centaurus.
Globular clusters are some of the oldest objects in our universe. Their
stars are over 12 billion years old, and, in most cases, formed all at
once when the universe was just a toddler. Omega Centauri is unusual in
that its stars are of different ages and possess varying levels of metals,
or elements heavier than boron. Astronomers say this points to a different
origin for Omega Centauri than other globular clusters: they think it
might be the core of a dwarf galaxy that was ripped apart and absorbed by
our Milky Way long ago.
In this new view of Omega Centauri, Spitzer's infrared observations have
been combined with visible-light data from the National Science
Foundation's Blanco 4-meter telescope at Cerro Tololo Inter-American
Observatory in Chile. Visible-light data with a wavelength of .55 microns
is colored blue, 3.6-micron infrared light captured by Spitzer's infrared
array camera is colored green and 24-micron infrared light taken by
Spitzer's multiband imaging photometer is colored red.
Where green and red overlap, the color yellow appears. Thus, the yellow
and red dots are stars revealed by Spitzer. These stars, called red
giants, are more evolved, larger and dustier. The stars that appear blue
were spotted in both visible and 3.6-micron-, or near-, infrared light.
They are less evolved, like our own sun. Some of the red spots in the
picture are distant galaxies beyond our own.
Spitzer found very little dust around any but the most luminous, coolest
red giants, implying that the dimmer red giants do not form significant
amounts of dust. The space between the stars in Omega Centauri was
also found to lack dust, which means the dust is rapidly destroyed or
leaves the cluster.
