A swarm of twinkling old stars on the outskirts of the Milky Way shines in a new view from NASA's Hubble Space Telescope.
The prolific Hubble Space Telescope captured this image of the globular cluster IC 4499, which lies about 55,000 light-years away, in the Milky Way's outer halo — the cosmic hinterlands surrounding the galaxy's spiral-armed disk. NASA released the photo on Aug. 4.
Globular clusters are collections of old stars that orbit a host galaxy. Scientists have long thought that the stars inside a single globular cluster form at the about same time. But the most massive clusters can have multiple generations of stars because their immense gravity draws in more gas and dust that can then be cooked into new groups of stars.
The mass of IC 4499 puts it somewhere between the low-mass, single-generation globular clusters and the more massive, multi-generation globular clusters. But so far, all evidence on IC 4499 suggests it has only one stellar generation, according to NASA.
Most globular clusters are quite old. Initial estimates of IC 4499 from the 1990s suggested this bunch of stars was surprisingly young. But follow-up observations with Hubble have shown that IC 4499, like most of the galaxy's globular clusters, is about 12 billion years old, according to NASA. That's quite ancient, considering the universe got its start approximately 13.8 billion years ago. For comparison, Earth's sun was born about 4.6 billion years ago.
The Hubble Space Telescope launched in 1990, and for more than two decades, the telescope has beamed back amazing images of the cosmos from its perch high above the clouds, free of the distortion of Earth's atmosphere.
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