Betelgeuse is a semiregular variable star located approximately 640 light-years from the Earth. Semiregular variable stars are giants or supergiants of intermediate and late spectral type showing considerable periodicity in their light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curves may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter).
The future fate of this star depends on its mass; as it probably contains more than 15 solar masses, it will continue to burn and fuse elements until the core is iron, at which point Betelgeuse will explode as a type II supernova. During this event the core will collapse, leaving behind a neutron star remnant some 20 km in diameter. However, if Betelgeuse is at the lighter end of estimated mass, it may instead contract to become a white dwarf.
Considering its size and age of 8.5 million years, old for its size class, Betelgeuse may explode within the next thousand years. At the current distance of Betelgeuse from the Earth, such a supernova explosion it would be the brightest recorded; outshining the Moon in the night sky and becoming easily visible in broad daylight.
The supernova would brighten to apparent magnitude –12 over a two week period, then remain at that intensity for two or three months before rapidly dimming. The year following the explosion, radioactive decay of cobalt to iron will dominate emission from the supernova remnant, and the resulting gamma rays will be blocked by the expanding envelope of hydrogen. If the neutron star remnant became a pulsar, then it might produce gamma rays for thousands of years.
