Credit: NASA, ESA, and the Hubble SM4 ERO Team, July 2009

Wow.  Fresh from the newly upgraded Hubble, the center of globular cluster Omega Centauri (NGC 5139).  Discovered by Edmond Halley in 1677 (who thought it was a nebula), Ptolemy thought the cluster was a single star 2000 years ago, and listed it in his catalog as such. In this image you see many yellow-white stars smaller than the sun (the little tiny ones), some yellowish-orange stars that are red giants (is “yellowish” a word?), and a scattering of blue, short-lived hot stars.  The cluster is about 12 billion years old, and contains stars of many different ages.  It can be seen with the naked eye in the southern constellation Centaurus.  At a magnitude of 3.7, it looks like a small, dim smudge.

Thought now possibly to be the core of a dwarf galaxy ripped apart by the Milky Way, and absorbed, astronomers report evidence of an intermediate-mass black hole in the center of the globular cluster.  The stars are being pulled toward the center and packed in almost 10,000 times more densely than in the neighborhood of our sun.  The stars are believed to be about 0.1 light years apart.

This is what Omega Centauri looks like in the sky:

A wide star field image of the region around Omega Centauri (NGC 5139).
The field-of-view is approximately 4.6 x 4.1 degrees.
Credit: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)

Ptolemy thought it was a giant star, Edmond Halley a nebula, but in the 1830s English astronomer John Hershel was the first to call Omega Centauri a globular cluster.  With the new information available through Hubble ST, Omega Centauri may soon be reclassified.

Scientists estimate the size of the dwarf galaxy possibly associated with Omega Centauri at 10 million solar masses, and the black hole in it’s center to be 40,000 solar masses.  We will hear more from Omega Centauri in the future study of black holes.

http://msowww.anu.edu.au/news/media_releases/media_release_030716.php
http://www.spacetelescope.org/news/html/heic0809.html