Presence of A Central Black Hole
A 2008 study presented evidence for an intermediate-mass black hole at the center of Omega Centauri, based on observations made by the Hubble Space Telescope and Gemini Observatory on Cerro Pachon in Chile. Hubble's Advanced Camera for Surveys showed that stars are bunching up near the center of Omega Centauri, as evidenced by the gradual increase in starlight near the center. Using instruments at the Gemini Observatory to measure the speed of stars swirling in the cluster's core, E. Noyola and colleagues found that stars closer to the core are moving faster than stars farther away. This measurement was interpreted to mean that unseen matter at the core is interacting gravitationally with nearby stars. By comparing these results with standard models, the astronomers concluded that the most likely cause was the gravitational pull of a dense, massive object such as a black hole. They calculated the object's mass at 4.0 x 104 solar masses.
However, more recent work has challenged these conclusions, in particular disputing the proposed location of the cluster center. Calculations using a revised location for the center found that the velocity of core stars does not vary with distance, as would be expected if an intermediate-mass black hole were present. The same studies also found that starlight does not increase toward the center but instead remains relatively constant. The authors noted that their results do not entirely rule out the black hole proposed by Noyola and colleagues, but they do not confirm it, and they limit its maximum mass to 1.2 x 104 solar masses.
Read more about this topic: Omega Centauri
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