As such, their composition has a larger range of elements. Open clusters are also much younger, with the oldest being about a billion years old, according to the Harvard and Smithsonian Center for Astrophysics.
They contain just hundreds or thousands of stars, making them far less dense than globular clusters. Unlike globular clusters, open clusters, also known as galactic clusters, do not have a distinct shape their stars are loosely clustered together in an amorphous gravitationally bound group. M13 was discovered by Halley in 1714, and Charles Messier added it to his famous catalog in 1764, though he originally believed that it contained no stars at all. John Herschel correctly determined it to be a globular cluster in the 1830s. Although Ptolemy spotted Omega Centauri in the second century AD, he mistakenly believed it was a star Edmond Halley later misidentified it as a nebula in 1677, according to NASA. Some of the most famous globular clusters include Omega Centauri, the largest known globular cluster in our galaxy per NASA, and M13, one of the brightest. In contrast, the Andromeda galaxy has some 400, and the M87 galaxy has more than 10,000, according to the Harvard and Smithsonian Center for Astrophysics.
(Those elements would be created later on by supernovas.) Because globular clusters have little gas and dust left, they no longer produce new stars, per the ATNF.Īstronomers have discovered approximately 150 globular clusters in the Milky Way galaxy. Because they are so old, they are " metal-poor," meaning they lack the heavy elements that did not exist in the early universe. Stars in globular clusters formed in the early days of the universe, around 10 billion years ago, according to the Harvard and Smithsonian Center for Astrophysics, making them some of the oldest stars in existence. But a telescope reveals their true form: thousands to millions of stars form a spherical shape with a bright, dense core. If viewed with the naked eye, globular clusters look like faint smudges of light against the darkness of space. This image was taken by the Hubble Space Telescope, which is run by ESA and NASA.
Globular star cluster NGC 6717 is located about 20,000 light-years from Earth, according to the European Space Agency (ESA). There are three main types of star clusters: globular clusters, open clusters, and stellar associations, each of which has different properties that provide different information to astronomers. Comparing the two "helps you understand what's going on on the insides of the stars and how they evolved throughout their lifetimes," according to Steffen.
"If you have a star cluster that's 100 million years old, and then you have a star cluster that's a billion years old, you basically have two snapshots of the lives of stars," Steffen said. Stars within a galaxy, on the other hand, can be a variety of ages and have a variety of compositions, Steffen said. That's why stellar clusters are so important to astronomers who are studying stellar evolution. Another factor that differentiates star clusters from galaxies is that within each cluster, stars are roughly the same age and made from roughly the same materials, given that they formed from the same molecular cloud, according to the Australia Telescope National Facility (ATNF).
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