BETELGEUSE (ALPHA ORIONIS), by Jim Kaler

BETELGEUSE (ALPHA ORIONIS), by Jim Kaler

Postby admin » Mon Nov 16, 2015 4:04 am

BETELGEUSE (ALPHA ORIONIS)
by Jim Kaler

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Image
Hubble Space Telescope Captures First Direct Image of a Star. This is the first direct image of a star other than the Sun. Called Alpha Orionis, or Betelgeuse, the star is a red super giant, a Sun-like star nearing the end of its life. The Hubble picture reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar behemoth's surface. The enormous bright spot, more than 10 times the diameter of Earth, is at least 2,000 degrees Kelvin hotter than the star's surface. Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland

The great star Betelgeuse is one of the two that dominate mighty Orion of northern winter, the other Rigel, the pair respectively called Alpha and Beta Orionis. The name Betelgeuse is a corruption of the Arabic "yad al jauza," which means the "hand of al-jauza," al-jauza the ancient Arabs' "Central One," a mysterious woman. For us, it marks the upper left hand corner of the figure of the Greek's ancient hunter (and since he is facing you, his right shoulder). One of the sky's two first magnitude supergiants (the other Antares of northern summer), Betelgeuse is one of the larger stars that can be seen, indeed one of the larger stars to be found anywhere. Typically shining at magnitude 0.7, this class M (M1.5) red supergiant (with a temperature of about 3600 Kelvin) is a semi-regular variable that changes between magnitude 0.2 and 1.5 over multiple periods between roughly half a year and 6 years. At its most likely distance of 425 light years, its measured angular diameter yields a radius 600 times that of the Sun, 2.8 Astronomical Units. If placed at the Sun, the star would go 55% of the way to the orbit of the planet Jupiter. From its size and temperature, allowing for its infrared radiation, Betelgeuse shines an amazing 60,000 times brighter than our Sun, which coupled with the temperature also gives a radius of 2.8 AU. However, the star is ejecting part of itself through a strong wind, and is surrounded by a huge shell of dust of its own making. That, an extended atmosphere, and the pulsations make it difficult to locate an actual "surface" and to tell just how large the star actually is. Even the distance is subject to uncertainty, the luminosity ranging from 40,000 solar to 100,000 solar. Whatever the actual numbers, Betelgeuse is clearly a highly evolved star, one whose central hydrogen fuel supply has run out. As a result, the core contracted into a hot dense state, and the outer portions swelled outward. We do not really know the star's condition at the moment, but the odds are that it is now in the process of fusing helium into carbon and oxygen in its core. From theory, its initial mass should have fallen somewhere between 12 and about 17 times that of the Sun which suggests that the core will fuse elements through neon, magnesium, sodium, and silicon all the way to iron. It will then collapse, and Betelgeuse will blow up as a supernova, most likely leaving a compact neutron star about the size of a small town behind. If it were to explode today, it would become as bright as a crescent Moon, would cast strong shadows on the ground, and would be seen easily in full daylight.
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