A small region inside the massive globular cluster Omega Centauri which boasts nearly 10 million stars. The stars in Omega Centauri are about about 16,000 light-years from Earth, and are between 10 billion and 12 billion years old. The majority of the stars in the image are yellow-white, like our Sun. These are adult stars that are shining by hydrogen fusion. Toward the end of their normal lives, the stars become cooler and larger. These late-life stars are the orange dots in the image. Even later in their life cycles, the stars continue to cool down and expand in size, becoming red giants. These bright red stars swell to many times larger than our Sun\'s size and begin to shed their gaseous envelopes. After ejecting most of their mass and exhausting much of their hydrogen fuel, the stars appear brilliant blue. Only a thin layer of material covers their super-hot cores. These stars are desperately trying to extend their lives by fusing helium in their cores. At this stage, they emit much of their light at ultraviolet wavelengths. When the helium runs out, the stars reach the end of their lives. Only their burned-out cores remain, and they are called white dwarfs (the faint blue dots in the image). White dwarfs are no longer generating energy through nuclear fusion and have gravitationally contracted to the size of Earth. They will continue to cool and grow dimmer for many billions of years until they become dark cinders. All of the stars in the image are cozy neighbors. The average distance between any two stars in the cluster\'s crowded core is only about a third of a light-year, roughly 13 times closer than our Sun\'s nearest stellar neighbor, Alpha Centauri. Although the stars are close together, WFC3\'s sharpness can resolve each of them as individual stars. If anyone lived in this globular cluster, they would behold a star-saturated sky that is roughly 100 times brighter than Earth\'s sky. Hubble observed Omega Centauri on July 15, 2009, in ultraviolet and visible light. (NASA, ESA, and the Hubble SM4 ERO Team)
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