Omega Centauri

An international team of astronomers has used more than 500 images from NASA's Hubble Space Telescope – spanning two decades of observations – to detect seven fast-moving stars in the innermost region of the globular star cluster Omega Centauri, the largest and brightest globular cluster in the sky. These stars provide new compelling evidence for the presence of the gravitational pull from an intermediate-mass black hole (IMBH) tugging on them. Only a few other IMBH candidates have been found to date.

Omega Centauri is visible from Earth with the naked eye and is one of the favorite celestial objects for stargazers living in the southern hemisphere. Although the cluster is 17,700 light-years away, located just above the plane of the Milky Way, it appears almost as large as the full Moon when seen from a dark rural area. The exact classification of Omega Centauri has evolved through time, as our ability to study it has improved. It was first listed in Ptolemy's catalog nearly 2,000 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 recognize it as a globular cluster. Omega Centauri consists of roughly 10 million stars that are gravitationally bound. The cluster is about 10 times as massive as other big globular clusters – almost as massive as a small galaxy.

About the colours

These images are a composite of separate exposures acquired by the WFC3/UVIS instrument on the Hubble Space Telescope. Several filters were used to sample various wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Blue= F275W + F336W + F438W, Green= F606W + F625W, Red= F658N + F814W

About the data

The HST observations include those from programs 9442 (A. Cool), 10252 (J. Anderson), 10775 , (A. Sarajedini), 12193 (J. Lee), 13066 (L. Smith), 13606 (J. Anderson), 15594 (V. Kozhurina-Platais), 15764 (N. Hathi), 15857 (A. Bellini), 16380 (M. Chiaberge), 16384 (Y. Cohen), 16520 (N. Hathi), 16968 (N. Hathi), 11452 (J. Quijano), 11011 (C. Kochnek), 12094 (L. Petro), 12339 (E. Sabbi), 12353 (V. Kozhurina-Platais), 12580 (A. Renzini), 12694 (K. Long), 12700 (A. Riess), 12714 (V. Kozhurina-Platais), 12802 (J. MacKenty), 13100 (V. Kozhurina-Platais), 13570 (V. Kozhurina-Platais), 14031 (V. Kozhurina-Platais), 14393 (V. Kozhurina-Platais), 14550 (V. Kozhurina-Platais), 14759 (T. Brown), 15000 (V. Kozhurina-Platais), 15593 (V. Kozhurina-Platais), 15594 (V. Kozhurina-Platais), 15733 (V. Kozhurina-Platais), 15857 (A. Bellini), 16117 (M. Reinhart), 16514 (R. Bohlin), 16441 (J. Anderson), 16588 (V. Kozhurina-Platais), 16777 (A. Seth), and 17023 (C. Martlin).

This dataset contains HST observations of the globular cluster Omega Centauri out to its half-light radius. The data were selected to contain all available observations with filters suitable for high-precision astrometry (ACS/WFC: F435W, F475W, F555W, F606W, F625W, F775W, F814W; WFC3/UVIS: F336W, F390W, F438W, F555W, F606W, F775W, F814W). In addition, the filters ACS/WFC F658N and WFC3/UVIS F275W were added for photometric purposes as they also cover almost the entire half-light radius. The data were taken in the time spanning from June 2002 to March 2023. They have been collectively compiled here .