In September of 2006, astronomers observed the brightest supernova ever, by far. The image shows SN2006gy, which outshines its own galaxy with an intrinsic brightness 100 times that of a typical supernova.  Moreover, SN2006gy’s brightness changes far more slowly than a typical supernova—70 days passed from the first observation of the explosion to maximum brightness, and eight months later it was still brighter than a typical supernova (see light curves). From this brightness, its mass was estimated to be about 150 times the mass of the Sun. 

This is an infrared image of SN2006gy and the nucleus of its galaxy. For comparison, a typical supernova is about as bright as its galaxy. (image credit: Lick/UC Berkeley/J. Bloom & C. Hansen)

These graphs show light curves for various supernovas.  Note how slowly SN2006gy's curve changes compared to the others, and how much brighter it was. (image credit: Nathan Smith, UC Berkeley)

This Hubble image shows lEta Carinae, an extremely large star in the Milky Way that survived an outburst about 150 years ago. This star is a potential supernova.  (image credit: J. Morse [U. Colorado], K. Davidson [U. Minnesota], STScI, and NASA)

Some astrophysicists hypothesized that this star was a white dwarf in a binary system that was accreting mass from the companion. In this model, the white dwarf ultimately would explode into the hydrogen it was accreting and produce an intense x-ray flux.  To test this idea, the Chandra telescope observed SN2006gy in x-rays, and the results were too small by a factor of about a million to fit the accreting white dwarf model.

Although we on Earth reside at a safe distance—about 24 million light years—from SN2006gy, we have an ominous-looking neighbor right here in our own Milky Way, a mere 2500 light-years away (see image). This star, Eta Carinae, has a mass of between 100 to 120 solar masses, so it's one of the largest stars in our galaxy. It also has a lurid history (see table below), including a "false supernova" explosion in 1843, which split it into two spherical lobes separated by a thin disk, as shown in the image.

With its great mass and history of instability, Eta Carinae is certainly a potential supernova. If it were to explode, it could emit powerful jets of gamma radiation, which would threaten the Southern Hemisphere, but fortunately these jets are narrow and well separated. In any case, astronomers plan to keep a close watch on this star in the future.