DISCOVERY/ The sources of gas that keep the Milky Way going

The source of the gas that keeps the Milky Way and our entire galaxy alive was discovered by two researchers from the University of Notre Dame, Nicolas Lehner and Christopher Howk. This source of ionized gas, discovered using the Hubble space telescope (launched into space in 1990, found in the outmost layers of Earth’s atmosphere, about 560 kilometers away, and managed by NASA and the European Space Agency) had never before been identified.

Ilsussidiario.net interviewed one of the two researchers, Nicolas Lehner, to find out more about this extremely important discovery. “How does the gas cycle in and out of galaxies? What are the flows of matter and energy in the halo? What controls the mass-energy-chemical cycles within galaxies?” asked Lehner. “These are all key questions that astronomers and cosmologists want to answer, and that we set out to answer.” Thus, it was a study with great ambitions: the evolution of the galaxy and the formations of its elements after the Big Bang. As Lehner states, “These large-scale flows directly affect the evolution of the galaxies and the intergalactic medium, and large cosmological simulations predict their critical role in galaxy formation and evolution. This and upcoming observational results signal progress toward answering some of the most crucial open questions in galaxy formation studies”.

One might say, then, that this research was born from the certainty that new stars continue to be formed today. “Exactly,” explains Lehner, “Our Galaxy, the Milky Way, and in fact every galaxy, would rapidly change all its gas into stars if no supply of new matter were available to replenish the gas. Therefore, we know that the gas has to come from somewhere because we know that new stars are still being formed. Astronomers have hypothesized that the ionized fast-moving gas clouds could be this reservoir of gas, but it was not known if they were interacting with the Milky Way. Our study demonstrates that they are indeed the long sought reservoir for continuing star formation in the Milky Way”.

Technically, how did you arrive at your discovery? “To solve the problem, we identified 27 stars around the Milky Way, whose distances were known, and used the Hubble to take line-of-sight readings of light coming from them.” What did that tell you?