Ů��С��Ƶ

The wind blowing from the centre of our galaxy carries a surprising cargo. It appears to be pushing two dense clumps of gas, and these strange clouds are moving far faster than they should be. As they hurtle away from the centre of the Milky Way, this could wreak havoc on star formation.

The centre of the Milky Way is a chaotic place, full of high-energy processes like star formation and matter falling into the supermassive black hole there. All that energy blows gas – mostly hydrogen – away from the galactic centre in what is called the galactic wind.

Enrico Di Teodoro at Johns Hopkins University in Maryland and his colleagues used the Atacama Pathfinder Experiment, a radio telescope in Chile, to observe this process. Most of the gas is relatively hot and tenuous, but they spotted two clouds of much colder, more dense gas being blown towards the outer reaches of the galaxy.

“This was quite unexpected,” says Di Teodoro. Most of the gas in the galactic wind is very light so it’s easy to push out of the centre of the galaxy, but these clouds are heavier. Nevertheless, they are moving at speeds up to 300 kilometres per second.

“The problem with the Milky Way is that we don’t have enough energy to move around these clouds of gas like this,” says Di Teodoro. “It’s like if you are trying to move a baseball by blowing on it.” It isn’t yet clear where the energy is coming from to accelerate these dense clumps to high speeds.

The type of hydrogen that is predominant in the two cold gas clouds is the same type that is usually used to build up stars, so its unexpected expulsion from the centre of the galaxy could have major consequences. “We could be observing a process that in a few billion years will bring the galaxy to be quiet and not forming stars anymore in that region,” says Di Teodoro. If these cold clouds are common, it could change star formation around the entire galaxy.