Do black holes help build stars?

We usually think of black holes as cosmic destroyers, heartlessly devouring anything — even a star — that enters their enormous gravitational pull. But there might be another, more helpful side to supermassive black holes that we're only just discovering.

A team of researchers in Australia and the United Kingdom say they've discovered something very unusual in the nearby galaxy Centaurus A: its central, supermassive black hole actually seems to be helping new stars to form. We know that black holes can become "switched on", supercharging the material around it and pushing it away, which creates a phenomenon known as an "outflow." These outflows smashes through star-forming gas found elsewhere in the galaxy, heating and compressing the gas as it passes by.

In a statement, the Royal Astronomical Society explains how the astronomers used data — some of which you can see in the image up top — from the Hubble telescope's Wide Field Camera 3 to study the effects of these outflows:

With WFC3, the scientists took a close look at the 'inner filament', a region located close to the outflow that is a source of ultraviolet and X-ray emission, as well as being bright in visible light. Using the Hubble images, the team were then able to map out the star formation history of the filament with unprecedented accuracy.

They found that the tip of the filament closest to the outflow contains young stars, the ages of which are similar to the time since the outflow 'switched on' but that there are no young stars further up the filament. This is exactly what is expected from an outflow overrunning a cloud of gas sitting in its path. The densest central parts of the cloud are compressed and collapse to form stars, while the gas on the outskirts is swept away from the tip of the filament, like a pile of autumn leaves in the wind.

Without the black hole's outflows, the gas might never have become tightly compressed enough to start the formation of new stars. Team leader Dr. Stanislav Shabala of the University of Tasmania says that these black hole outflows would have been particularly important in the early universe, when galaxies were full of dense pockets of gas just waiting to start coalescing into stars.

Via Monthly Notices of the Royal Astronomical Society. Image of the inner filament by Mark Crockett.