No stars? Blame the black holes

Contrary to what was believed until now, astronomers have discovered that despite the complete absence of star formation some giant elliptical galaxies contain large amounts of cold gas. The lack of production of new stars in them would then be attributed to the activity of the jets of their central black holes.

galaxy NGC 5044

The elliptical galaxy NGC 5044.

Credit: NASA Chandra

On paper, the giant elliptical galaxies appear to be among the least interesting of the entire universe: it is always thought that does not happen much in these parts, in the absence of spiral arms and the lack of star formation. But like any self-respecting detective story, even the great myths and raw outskirts of the universe can hide small mysteries and crimes. And it’s a new study based on data Herschel Space Observatory to lift the veil on the dynamics still unclear that come to life within these galaxies.

Since that host only old stars and the fact that non availability of the new time, astronomers are accustomed to call the giant elliptical galaxies “red and dead”. Until now it was believed that the lack of star formation depended on the limited availability of the right fuel, or cold gas in those areas. Without a good deal of vital raw material, it cannot form stars, purely and simply. Certainly the absence of cold gas created some problems of interpretation: there were issues because it was somehow ejected from galaxies or because it was already used all the old formation of the first stars? A sweep this view of things we thought the new research, published in the Monthly Notices of the Royal Astronomical Society. “We examined eight giant elliptical galaxies that no one had studied first with Herschel and we were delighted to discover that, contrary to what was believed earlier, six out of eight are full of cold gas,” says Norbert Werner, a researcher at Stanford University in California, who led the study. “Even if we detect cold gas, there is no sign of ongoing star formation,” says co- author Raymond Oonk of ASTRON, the Netherlands Institute for Radio Astronomy. “And this is bizarre: with a lot of cool gas available, why these galaxies do not form stars?”

Faced with these new questions researchers have tried to give an answer. These galaxies, they argue, are not the funeral we thought: the responsibility for the failure of star formation would in fact be attributed to the activity of the black holes in galaxies. “In the six cold gas-rich galaxies, the data show that the hot gas cools,” says Werner. This is in agreement with theoretical expectations: Once cooled, the gas at high temperatures becomes warm and cold gas that is observed at wavelengths longer. However, the cold gas in these galaxies would not be able to take the next step, which condense and form stars, just because of the jet black holes. In some theoretical models, in fact, the level of activity of a black hole could explain why the gas in a galaxy is able or not to form stars. The black holes would be in fact part of the huge cosmic bullies, preventing the birth of new stars, and the findings of Werner and colleagues would seem to fit like a glove these theoretical models. “These galaxies are red , but with the black giant holes in their hearts pumping for sure are not dead ,” said Werner .

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