Among them was this puzzle. Ellipticals, on the other hand, contain very little gas but possess many globular clusters. It's almost like saying 2 plus 2 equals 8. Our Milky Way galaxy, a spiral, has about 150 globular clusters while an elliptical with the same brightness would contain about 600 globulars. These dissenting astronomers did not consider the important role that gas plays in mergers.
Most mergers involve gas being compressed, which triggers intense star formation.
A Burst of Infant Stars Astronomers studying colliding galaxies hoped that a new infrared satellite would provide some clues. They weren't disappointed. This survey revealed that the most luminous galaxies in the infrared part of the spectrum were always colliding galaxies, illuminated by dust surrounding a burst of infant stars. The images provided evidence that interacting galaxies showed signs of unusually vigorous star formation, a theory that originally had been proposed by Zwicky and Arp. When two galaxies collide, their interstellar gas is compressed into thick clouds.