It is getting ready to go nova. Isn't that how we have always been told it happens? First a contraction and then...BOOM!
Supernova, rather than a nova.
http://en.wikipedia.org/wiki/Betelgeuse
Betelgeuse... (a Ori, a Orionis, Alpha Orionis) is a semiregular variable star located approximately 600 light-years away from Earth. It is the second brightest star in the constellation Orion and the ninth brightest star in the night sky. Although Betelgeuse has the Bayer designation alpha, Rigel (Beta Orionis) is usually brighter (Betelgeuse is a variable star and is on occasion brighter than Rigel). The star is a vertex of the Winter Triangle asterism.
Betelgeuse is a red supergiant, relatively luminous, and one of the largest stars known. For comparison, if the star were at the center of our solar system its surface might extend out to between the orbits of Mars and Jupiter, wholly engulfing Mercury, Venus, Earth and Mars. 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.
Astronomers believe Betelgeuse is only a few million years old, but has evolved rapidly because of its high mass. Some astronomers believe it may become a supernova within a timeframe where it could be observable by human civilization.
[okay, sometimes wiki-wacky is a confused mess]
http://en.wikipedia.org/wiki/Red_supergiant
Stars with more than about 10 solar masses after burning their hydrogen become red supergiants during their helium-burning phase. These stars have very cool surface temperatures (3500-4500 K), and enormous radii. The five largest known red supergiants in the Galaxy are VY Canis Majoris, VV Cephei A, V354 Cephei, RW Cephei and KW Sagittarii, which all have radii about 1500 times that of the sun (about 7 astronomical units, or 7 times as far as the Earth is from the sun). The radius of most red giants is between 200 and 800 times that of the sun, which is still enough to reach from the sun to Mars and beyond... The mass of many red supergiants allow them to eventually fuse elements up to iron. Near the end of their lifetimes, they will develop layers of heavier and heavier elements with the heaviest at the core... The red supergiant phase is relatively short, lasting only a few hundred thousand to a million or so years. The most massive of the red supergiants are thought to evolve to Wolf-Rayet stars, while lower mass red supergiants will likely end their lives as a type II supernova.
http://en.wikipedia.org/wiki/Wolf-Rayet_star
Wolf-Rayet stars (often referred to as WR stars) are evolved, massive stars (over 20 solar masses), which are losing mass rapidly by means of a very strong stellar wind, with speeds up to 2000 km/s. While our own Sun loses approximately 10-14 solar masses every year, Wolf-Rayet stars typically lose 10-5 solar masses a year.
Wolf-Rayet stars are very hot, with surface temperatures in the range of 25,000 K to 50,000 K. It is believed that the star in the galaxy NGC 2770 that exploded into a supernova on January 9, 2008 — SN 2008D, the first supernova ever observed in the act of exploding — was a Wolf-Rayet star.
http://en.wikipedia.org/wiki/Supernova#Type_II
When the core’s supply of hydrogen is exhausted, this outward pressure is no longer created. The core begins to collapse, causing a rise in temperature and pressure which becomes great enough to ignite the helium and start a helium-to-carbon fusion cycle, creating sufficient outward pressure to halt the collapse. The core expands and cools slightly, with a hydrogen-fusion outer layer, and a hotter, higher pressure, helium-fusion center. (Other elements such as magnesium, sulfur and calcium are also created and in some cases burned in these further reactions.)
This process repeats several times, and each time the core collapses and the collapse is halted by the ignition of a further process involving more massive nuclei and higher temperatures and pressures. Each layer is prevented from collapse by the heat and outward pressure of the fusion process in the next layer inward; each layer also burns hotter and quicker than the previous one — the final burn of silicon to nickel consumes its fuel in around one day, or a few days. The star becomes layered like an onion, with the burning of more easily fused elements occurring in larger shells. In the later stages, increasingly heavier elements undergo nuclear fusion, and the binding energy of the relevant nuclei increases.
http://apod.nasa.gov/apod/ap980419.html
Here is the first direct picture of the surface of a star other than our Sun. Taken by the Hubble Space Telescope in 1995, the atmosphere of Betelgeuse reveals some unexpected features, including a large bright hotspot visible below the center. Betelgeuse (sounds like “beetle juice”) is a red supergiant star about 600 light years distant, easily recognizable from its brightness and reddish color in the constellation of Orion. While Betelgeuse is cooler than the Sun, it is more massive and over 1000 times larger. If placed at the center of our Solar System, it would extend past the orbit of Jupiter. Betelgeuse is nearing the end of its life and will become a supernova in a perhaps a few tens of millions of years.
Ooops, that earlier APOD link was from 1998! This is from info from 1995:
http://seds.org/hst/Btlgeuse.html
The Hubble image reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar behemoth’s surface. The enormous bright spot, more than ten times the diameter of Earth, is at least 2,000 Kelvin degrees hotter than the surface of the star.
The image suggests that a totally new physical phenomenon may be affecting the atmospheres of some stars. Follow-up observations will be needed to help astronomers understand whether the spot is linked to oscillations previously detected in the giant star, or whether it moves systematically across the star’s surface under the grip of powerful magnetic fields.
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970616b.html
[Tim Kallman for Ask an Astrophysicist]
Betelgeuse (also known as alpha ori) is a very large star, an M supergiant... For stars on the main sequence, which includes our Sun, there is simple proportionality between size and mass, and also a simple scaling for luminosity. For evolved stars the situation is less simple. Betelgeuse is more than 1000 times larger than the Sun, and 50000 times as luminous, but only about 20 times as massive. Most of the light from Betelgeuse comes out in the infrared, however, which is very different from the Sun. One consequence of the advanced evolutionary state of Betelgeuse is that it probably was much more massive when it was on the main sequence, and has already lost a significant fraction of its mass (probably more than half) in a stellar wind... A very crude estimate is that such stars spend 1% of their lives as supergiants, which would suggest 10,000,000 stars similar to Betelgeuse in our galaxy... Another one is Mira, in the constellation Cetus. Mira is probably larger than Betelgeuse, so large that it is thought that the outer layers of the star are barely held together by gravity. Mira is known to pulsate and eject its outer layers, probably in large part because of its weak gravity. Possibly the most massive known star is eta carina, which may have been 150 times as massive as the Sun when it first formed, and may be 50 - 60 times as massive as the Sun currently. In the 1830s eta carina underwent a tremendous outburst during which it became a brilliant naked eye object and ejected an amount of gas with mass approximately equal to the mass of the Sun. It is likely that the minimum main sequence mass for a star which will eventually make a black hole is 8 - 10 times the mass of our Sun. This is quite a bit less than Betelgeuse had when it was on the main sequence, and there are many such stars in our galaxy.
http://www.solstation.com/x-objects/betelgeuse.htm
Past observations have indicated that, partially because of roiling convection cells beneath its surface, the star’s surface has been observed to “wobble in and out” along with two pulsations, one restarting annually while the other cycles over six years. Based on long-term monitoring at 11.15 micrometers using the Infrared Spatial Interferometer at Mount Wilson Observatory, however, the star’s diameter appears to have progressively shrunk from 11.2 to 9.6 AUs; as the star’s radius is now just under about five times Earth’s orbit distance, having shrunk by a distance equal to the orbit of Venus. It is still unclear whether the star is experiencing a long-term oscillation in its size, undergoing initial contractions towards a collapse or a blow off of material related to its impending death as a red supergiant via a supernova, or simply rotating to present a different side of its bumpy surface (and so appear to change in size). Although the star appears spherically symmetrical at present, Townes and former graduate student Ken Tatebe had observed a bright spot on the surface of Betelgeuse in recent years.