‘Superbubbles’ of gas around quasars may form thanks to powerful winds

Astronomers have observed three distant quasars surrounded by enormous blobs of ionised gas termed “superbubbles”. These colossal blobs seem to be caused by winds whipping around the huge black holes that power the quasars, and the same winds may also be preventing their home galaxies from forming new stars.

Guilin Liu at the University of Science and Technology of China and his colleagues spotted these objects using the Gemini North telescope in Hawaii. They examined three red quasars – particularly bright examples of active supermassive black holes – and found that each one sat at the meeting point of a huge pair of bubbles of ionised gas. These hot gas clouds measured about 60,000 light years across, making them what astronomers call superbubbles.

The researchers then performed a series of simulations to figure out how these superbubbles were produced. We have long known that quasars create powerful winds and that these winds could have extreme effects on galaxies, but direct evidence has been tough to come by.

“We have made enormous efforts to actually detect outflows powerful enough to produce this effect,” says Liu. “We think we have enough evidence that the superbubbles reported in this paper are a consequence of powerful outflows we are after.”

As they create the superbubbles, these winds are also expected to heat up and blow away cooler gas. This gas is the raw material from which stars are made so when it is blown away, the star formation in the galaxy stalls out, resulting in an unexpectedly inactive galaxy. These new observations provide proof that this process really does occur.

It mostly seems to happen in galaxies that have recently undergone a merger. That merger feeds more material into the black hole, which causes higher activity and powerful winds that in turn create the bubbles. This could explain why galaxies tend to become quiescent after a merger instead of continuing to form stars. “If you live in one of [these galaxies] you will probably see two ‘Milky Ways’ crossing each other in the night sky,” says Liu. “A pair of superbubbles are there emitting green light, but they are extremely faint and extended in the sky, so they are likely very hard to be seen when you are very close to or even inside them.”