Just after the Big Bang the Universe's matter was almost entirely hydrogen atoms. Over time this gas of atoms came together and generated galaxies, stars and planets — and the process is still going on. Astronomers want to understand where, when and how the atomic gas is transformed to better understand the Universe in which we live. A new scientific study shows that the gas is distributed very differently today from how it was in the past, with much less in the galaxies' outer suburbs than billions of years ago. This means that it's much harder for galaxies to pull the gas in and form new stars and that is why stars are forming 20 times more slowly now than in the past."