The burst occurs over a region a few thousand light years in diameter. The most popular theory for the cause of a starburst is that it is triggered by a close encounter or collision with another galaxy. This collision sends shock waves rushing through the galaxy. These shock waves push on giant clouds of gas and dust, causing them to collapse and form a few hundred stars. The massive stars use up their fuel quickly and explode as supernovas, which produce more shock waves and more star formation. In this way, a chain reaction of star formation and supernovas can sweep through the central region of a galaxy, where most of the gas is located. When most of the gas is used up or blown away by the explosions, the starburst ends.
The infrared satellite IRAS discovered thousands of starburst galaxies. Many of the new stars remain surrounded by dust and gas for a million years. Their light is absorbed by the dust, which radiates away the heat as infrared radiation. The 'heat radiation' produced by hot sidewalks on a summer day is infrared radiation. Starburst galaxies are rare among nearby galaxies, but they were common many billions of years ago. The universe is expanding, so galaxies were much closer together in the past and collisions or close encounters were more frequent, causing more starbursts.
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James Clerk Maxwell