Omega Centauri is the brightest and largest globular cluster in the Milky Way. In fact, Omega Centauri is so bright that for centuries it was believed to be an individual star. In actuality, Omega Centauri is a huge globular cluster containing millions of old red and yellow stars. Omega Centauri is around 170 light years across and is about 16,000 light years away from Earth.
Like several other known globular clusters, the core of Omega Centauri is dominated by a black hole with a mass of 40,000 suns. Astronomers are still unsure exactly how black holes such as these form. Rather than being stellar black holes, which form when massive stars go supernova, or supermassive black holes located at the cores of massive galaxies, black holes such as the one located in Omega Centauri are intermediate-mass black holes. However, one theory suggests that these black holes form from several smaller black holes merge together. Another mystery of Omega Centauri is the discovery of massive blue stars. Astronomers believe that Omega Centauri is around 12 billion years old (around the same age as the Milky Way itself), so any stars that are both hot and massive enough to shine blue should have long since aged and died. However, one explanation for how these stars exist is that they form when two lower-mass red stars happen to fall in orbit around each other and eventually merge with one another and form these blue stars.
The above image of Omega Centauri was one of the first images taken with Hubble’s Wide Field Camera-3. Both ultraviolet and visible data have been combined to show colour differences, which has revealed a wide range of star types. The vast majority of stars within Omega Centauri are lower-mass yellow and red stars, some not too different from our sun.
Image credit: NASA/ESA
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