A major mystery in the evolution of galaxies appears to have been solved by scientists. Researchers say intense winds from supermassive black holes prevent some galaxies from forming new stars, turning them into cosmic graveyards, or red geysers as they have been dubbed.
While galaxies begin their lives full of gas and dust, many end up becoming red geysers – featureless wastelands where no stars form and remain in this state for the rest of their lives. What causes this barren landscape was not known, however.
An international team of researchers led by Edmond Cheung, from the University of Tokyo's Kavli Institute for the Physics and Mathematics of the Universe, looked at a new large survey of galaxies and found a common trait among these red geysers.
They said that to stop star formation something must be removing or heating up the gas present to stop it from cooling processes needed for stars to form. Study co-author Michele Cappellari said: "Stars form from the gas, a bit like the drops of rain condense from the water vapour. And in both cases one needs the gas to cool down, for condensation to occur.
"But we could not understand what was preventing this cooling from happening in many galaxies. But when we modelled the motion of the gas in the red geysers, we found that the gas was being pushed away from the galaxy centre, and escaping the galaxy gravitational pull."
The team found the cooling was being prevented by strong stellar winds – winds that would be produced by low-energy supermassive black holes. Published in Nature, the team looked specifically at a distant red geyser called Akira. They showed the mechanism driving the stellar wind probably came from Akira's galactic nucleus. Energy from this, powered by a supermassive black hole, was enough to produce the wind.
Cheung said: "Stars form from the gas, but in many galaxies stars were found not to form despite an abundance of gas. It was like having deserts in densely clouded regions. We knew quiescent galaxies needed some way to suppress star formation, and now we think the red geysers phenomenon may represent how typical quiescent galaxies maintain their quiescence."