Red Supergiants

A star of 15 solar masses exhausts its hydrogen in about one-thousandth the lifetime of our sun. It proceeds through the red giant phase, but when itreaches the triple-alpha process of nuclear fusion, it continues to burn for a time and expands to an even larger volume. The much brighter, but still reddened star is called a red supergiant. Betelgeuse, at the shoulder of Orion, is the best-known example. Absolute luminosities may reach -10 magnitude compared to +5 for our sun.

Some of these supergiants are unstable and form the very importantCepheid variables. In their finalstages, supergiants may explode intosupernovae. The collapse of these massive stars may produce a neutron star or a black hole.

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Betelgeuse

Betelgeuse is a prominent example of a red supergiant star. It is located at the shoulder of Orion. It forms part of the winter triangle seen from North America. Betelgeuse has a luminosity about 10,000 times that of the Sunand its radius is calculated to be about 370 times that of the sun.

If it were positionedat the center of our sun, its radius would extend out past the radius of Mars, about 2 astronomical units! Most stars on the main sequence have about the same size as the sun. It has a surface temperature of about 3000 K as determined from its blackbody radiation curve. Betelgeuse is about 310 light years away fromthe Earth. Its celestial coordinates are RA=5 h 52 m , dec=7° 24' .

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