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An open, nebulous star cluster in the constellation of Taurus, the Bull, the Pleiades are also known as The Seven Sisters, Messier 45, and M45. They are a relatively youthful group of approximately 500 tightly clustered stars, recent data measurements indicate that the Pleiades are around 100 million years old and about 380 light years from Earth. None of the stars has matured to the red giant stage yet, but, the brightest of them are hot blue-white giants. With an estimated lifespan of 250 million years, the stars will slowly move away from each other. Although the Pleiades is a young star cluster, some of the original stellar members are "White Dwarf Stars". One possible explanation for their quickened evolution is that incredibly massive stars became white dwarfs through an intensified process of stellar mass loss in planetary nebulae caused by rapid rotation, stellar winds, and siphoning by nearby stars. The white dwarfs are the residual star cores. The Pleiades stellar cluster also has many double and a few triple stars. Surveys of the Pleiades have revealed that about 170 stars are X-ray emitters, many of which emit X-rays at levels up to 1,000 times higher than the Sun. Beginning in 1995, "Brown Dwarf" stars have been detected in the Pleiades. Presumably they are observable in the infrared spectrum with probable masses around 10-60 times that of Jupiter, diameters equal to or less than that planet, and strong gravitational fields. The Pleiades open cluster is a brilliant neighbor for Earth. Open groups of stars are young galactic clusters formed from the same diffuse gas/dust cloud nebula which continue to orbit the Milky Way through the disk. As stellar siblings, they share many of the same properties and are held together by mutual gravitational attraction.
Although they have
different solar masses, they are all about the same age, chemical composition,
and distance. There are at least 1,100 known open clusters in the Milky Way
Galaxy.
A Reflection Nebula is a cloud of interstellar dust and gas that provides the basic matter for the generation of stars. Interestingly, nebula are also created by a form of cosmic recycling when dying stars shed a significant portion of their substance during the last days of their lives. Within the Pleiades cluster there are reflection nebula where several of the stars seem to be encircled by blue light threads because starlight is reflected off of tiny nearby particles of interstellar dust that scatters blue light that appears streaky because of the magnetic alignment between star fields. The Pleiades are part of the constellation of Taurus, the second sign of the astrological zodiac which the Sun passes through from mid-May to late June. There is a lot of mythology about "The Bull" since the animal was sacred to many ancient cultures. For instance, the ancient Egyptians viewed the constellation as their god Osiris; the Chinese as a "White Tiger" or "Great Bridge"; and the Greeks as a disguised Zeus in impassioned pursuit of the King of Phoenicia's daughter Europa. The diffuse Crab Nebula; the large, open, scattered, V shaped star cluster The Hyades; and, the red star Aldebaran are all part of this constellation. Stars are classified according to a spectrum where blue stars are hot and red stars are cool. A star's emission lines correlate with its color and surface temperature. There are seven spectral types which from hottest to coolest are O, B, A, F, G, K, and M. Spectral B-Type Blue Stars have surface temperatures that range from 11,000° to 25,000° Kelvin and burn helium.
The nine named stars of the
Pleiades are all hot B-Type Blue Stars. Such very bright B-Type Stars are rare;
while, dim M-Type Stars are common. By comparison, the Sun in our Solar System
is a G-Type Star.
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