No Doughnut Hole This… A True Cluster Hole Found By Hubble…
Omega Centauri has been known to be an unusual globular cluster for a long time. A new result obtained by Hubble and the Gemini Observatory has been announced by the European Space Agency that reveals that this newly found globular cluster may have a rare intermediate-mass black hole hidden in its center. This implies it is likely not a globular cluster at all, but a dwarf galaxy stripped of its outer stars. Omega Centauri, the largest and brightest globular cluster in the sky, is visible from Earth with the naked eye and is one of the favorite celestial objects for stargazers from the southern hemisphere. Although 17k light-years away, it located just above the plane of the Milky Way and appears almost as large as the full Moon when seen from a dark, rural area. Images obtained with the Hubble Space Telescope‘s Advanced Camera for Surveys and data from the GMOS spectrograph on the Gemini South telescope in Chile show that Omega Centauri appears to harbor an elusive and rare intermediate-mass black hole in its center.
The motions and brightness of the stars at the centre of Omega Centauri were measured. The measured velocities of the stars in the centre 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 centre of the cluster responsible for the fast-swirling dance of stars—almost certainly a black hole of about 40k solar masses. This discovery also has important implications on the very nature of Omega Centauri. Globular clusters contain up to one million old stars bound tightly by gravity and are found in the outskirts of many galaxies including our own. Omega Centauri already has several characteristics that distinguish it from other globular clusters: it rotates faster than average, its shape is highly flattened and it consists of several generations of stars, while typical globular clusters usually consist of just one generation of old stars. It is also about 10 times as massive as other big globular clusters, almost as massive as a small galaxy.
