Betelgeuse - Origin of the name "Betelgeuse", Distinguishing characteristics, The Star's Future

A red supergiant star, prominent in Orion, over 500 times the diameter of the Sun. Distance: 131 parsec.

Betelgeuse (Alpha (α) Orionis) (also written Betelguese and Betelgeux) is a semiregular variable star located 427 light-years away . It is the second brightest star in the constellation Orion, and the ninth brightest star in the night sky.

Betelgeuse is a red supergiant, one of the physically largest stars known. As it is, Betelgeuse is so large and so close that it is the star with the third largest angular diameter as viewed from Earth , smaller only than the Sun and R Doradus, and one of only a dozen or so stars that telescopes have imaged as a visible disk (See photo, at right and a picture of hotspots on Betelgeuse.) The angular diameter of Betelgeuse was first measured in 1920–1921 by Michelson and Pease using an astronomical interferometer on the Mount Wilson 100 inch telescope.

Origin of the name "Betelgeuse"

The name is a corruption of the Arabic يد الجوزا yad al-jawzā, or "hand of the central one".

Because of its rich reddish color the star has frequently been referred to as the "martial one", and in astrology portends military or civic honors. Other names are:

Al Dhira (the Arm), Al Mankib (the Shoulder) Al Yad al Yamma (the Right Hand) Ardra (Hindi, and name of Hindu Nakshatra), Bahu (Sanskrit), Besn (Persian) (the Arm), Gula (Euphratean), Ied Algeuze (Orion's Hand), Klaria (Coptic) (an Armlet) Yedelgeuse

It is known as 参宿四 (Shēnsùsì, the Fourth Star of the Constellation of Three Stars) in Chinese. The confusing name is due to the fact that the Constellation of Three Stars was originally composed of just three stars, all of them in the girdle of the Orion. Later, four more stars were added to this constellation, but the name remained unchanged.

Distinguishing characteristics

Several features of Betelgeuse are of particular interest to astronomers. It was one of the first stars to have its angular diameter measured with an astronomical interferometer; The distance to Betelgeuse is not precisely known, but if it is assumed to be 427 light years then the actual diameter varies between 500 and 800 times the Sun's diameter, making it roughly equivalent to the orbit of Jupiter.

The precise diameter is not easy to define, as the optical emission decreases very gradually with radius from the center of the star, and the color of the emission also varies with radius. It was also the first star to have starspots on its disk resolved in optical images by a telescope, first from Aperture Masking Interferometry and later from more detailed observations by the COAST telescope.

The Star's Future

Astronomers predict that Betelgeuse will ultimately undergo a type II supernova explosion although it is possible that the mass is low enough for Betelgeuse to leave a rare oxygen-neon white dwarf. Some regard the star's current variability as suggesting that it is already in the carbon burning phase of its life cycle, and will therefore undergo a supernova explosion at some time in the next thousand years or so. Skeptics dispute this contention and regard the star as being likely to survive much longer.

Even so, Betelgeuse would brighten at least 10,000 times as a supernova, causing it to shine with the luminosity of a crescent Moon.

Curiously, 1st century BC Chinese records unearthed by Shu-ren, Jianmin and Jin-Yi in 1980 refer to the color of Betelgeuse as being white or yellow. However, Ptolemy writing in 150 AD calls it a red star. Therefore, Fang Lizhi, a Chinese astrophysicist, proposed that Betelgeuse could have turned into a red giant star during that period. It is known that as stars use up the hydrogen fuel in their cores, their color changes from white to yellow to red. Thus, if their theory is right, it is unlikely that Betelgeuse will become a supernova any time soon because a star usually stays a red giant for tens of thousands of years.