March 17, 1999
Web posted at: 11:45 a.m. EST (1645 GMT)

INTERACTIVE:    Hubble 3-D VRML

(CNN) -- The Space Telescope Science Institute has released images taken by the Hubble Space Telescope of the most powerful cosmic explosion ever recorded.

The initial explosion came as an intense burst of gamma rays on January 23, 1999. For a moment, light from the burst was equal to the radiance of 100 million billion stars.

On February 8 and 9, when the Hubble telescope made observations, the blast had faded to a mere four-millionth of its original brightness. The images show the fading fireball embedded in a galaxy located 2/3 of the way to the horizon of the observable universe.

Hubble's resolution shows the galaxy is not the classical spiral or elliptical shape. Rather, it appears as finger-like filaments that extend above the bright wide fireball. NASA suggests the galaxy might be distorted by collision with another galaxy. This would cause the birth of millions of newborn stars.

Gamma rays, which have long been elusive and mysterious, go off about once a day. One theory suggests they are created by the merger of a pair of black holes, or a hypernova, thought to be a violently exploding star.

Hubble's observations support a theory that these powerful explosions occur where vigorous star formation takes place. Telescope images show the host galaxy is exceptionally blue, which scientists say indicates a large number of blue newborn stars.

Astronomers have known about gamma ray bursts for more than 20 years. However, the explosions have proved elusive because they happen with no warning, last only a few seconds, and can come from any region of the sky.

Astronomers do not fully understand the underlying mechanism behind gamma ray bursts. They are now using an armada of telescopes to gather more details of the January explosion, in the hopes of refining models to explain these mysterious events.

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