aIn 1978, two Yale astronomers, Richard
Larson and Beatrice Tinsley, discovered that some
aNow, computer simulations have shown how a collision can spark a star factory. As two agalaxies of unequal size meet, the gravitational tides induce a bar-shaped feature across the acenter of the bigger galaxy. The bar forms shock waves which knock the interstellar gas adown to a lower orbit, compressing it. Squeezed tightly together, the gas molecules fuse aand explode like hydrogen bombs all across the galactic core. The starburst lasts for ahundreds of millions of years.