I just read this interesting article on the Astromart site, although dated early February I hadn't seen or heard anything of this previously. I found it thought provoking indeed:
http://www.astromart.com/news/news.asp?news_id=812
I've selectively pasted some portions below to give you the gist, but read the full article to get the big picture.
" A new discovery has resolved some of the mystery surrounding Omega Centauri, the largest and brightest globular cluster in the sky. Omega Centauri appears to harbour an elusive intermediate-mass black hole in its center. "
" Exactly how Omega Centauri should be classified has always been a contentious topic. It was first listed in Ptolemy’s catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677. In the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster. Now, more than a century later, this new result suggests Omega Centauri is not a globular cluster at all, but a dwarf galaxy stripped of its outer stars.
Globular clusters consist of up to one million old stars tightly bound by gravity and are found in the outskirts of many galaxies including our own. Omega Centauri has several characteristics that distinguish it from other globular clusters: it rotates faster than a run-of-the-mill globular cluster, its shape is highly flattened and it consists of several generations of stars – more typical globulars usually consist of just one generation of old stars.
Moreover, Omega Centauri is about 10 times as massive as other big globular clusters, almost as massive as a small galaxy. These peculiarities have led astronomers to suggest that Omega Centauri may not be a globular cluster at all, but a dwarf galaxy stripped of its outer stars by an earlier encounter with the Milky Way. "
" ...measured the motions and brightnesses of the stars at the center of Omega Centauri. The measured velocities of the stars in the center are related to the total mass of the cluster and were far higher than expected from the mass deduced from the number and type of stars seen. So, there had to be something extraordinarily massive (and invisible) at the center of the cluster responsible for the fast-swirling dance of stars — almost certainly a black hole with a mass of 40 000 solar masses. "
" Before this observation, we had only one example of an intermediate-mass black hole — in the globular cluster G1, in the nearby Andromeda Galaxy "
" Although the presence of an intermediate-mass black hole is the most likely reason for the stellar speedway near the cluster’s center, astronomers have analyzed a couple of other possible causes: a collection of unseen burnt-out stars such as white dwarfs or neutron stars adding extra mass, or a group of stars with elongated orbits that would make the stars closest to the center appear to speed up. "
" Intermediate-mass black holes may be rare and exist only in former dwarf galaxies that have been stripped of their outer stars, but they could also be more common than expected, existing at the centers of globular clusters as well. A previous Hubble survey of supermassive black holes and their host galaxies showed a correlation between the mass of a black hole and that of its host. Astronomers estimate that the mass of the dwarf galaxy that may have been the precursor of Omega Centauri was roughly 10 million solar masses. If lower mass galaxies obey the same rule as more massive galaxies that host supermassive black holes, then the mass of Omega Centauri does match that of its black hole. "
Fascinating stuff!!!
