For more than a decade, astronomers have struggled to understand why there appear to be fewer stars in the universe than they expected.
Stars form when clouds of gas collapse due to gravitational attraction; but theoretical considerations and computer simulations of these processes have always suggested that their should be two or three times more stars in the night sky than we actually observe. So where are the missing stars?
Recently, using the Hubble Space Telescope, astronomers observed for the first time a distant galaxy in which the rapid formation of new stars is itself driving the raw materials for more stars out into space, and in the process slowing future star production. The raw materials being ejected are mostly hydrogen gas clouds, some containing the mass of more than a billion suns, and travelling at more than three million kilometres per hour! This is the first time this spectacular process has been observed.
This new discovery represents an important step forward in our understanding of galaxy evolution, and could certainly explain why the number of stars in the universe is lower than previously expected. For perspective, though, it is worth remembering that there are still far more stars in the observable universe than there are grains of sand on all the beaches in the world!
The presence of hydrogen gas is pivotal to successful star birth, and so astronomers suggest that by its removal, stellar factories within the galaxy are effectively shut down. The same mechanism may have halted an era of massive star formation in galaxies such as our own.