News in Science

Black hole UFOs stunt galaxy growth

Blowing in the wind The energy produced by monster black holes is enough to influence the evolution of entire galaxies, according to a new study.

The research, reported in the journal Science, provides the best proof yet that the growth of supermassive black holes found at the heart of galaxies directly controls galactic star formation.

"It's really astonishing that this supermassive black hole, no bigger than our solar system, is so powerful that it influences an entire galaxy, it's amazing when you think about it," says one of the study's authors Professor Fiona Harrison of the California Institute of Technology.

The researchers used combined data from the European Space Agency's XMM-Newton and NASA's NuSTAR Earth orbiting space telescopes to study the supermassive black hole at the centre of a quasar called PDS456.

This black hole is estimated to have ten billion times the mass of the Sun. By comparison the supermassive black hole at the centre of our galaxy the Milky Way called Sagittarius A* has just 4.3 million times the Sun's mass.

"Astronomers studying PDS456 knew material falling into this black hole is emitting a wind of out flowing particles and we want to know how much energy is in this wind, and whether it's enough to influence the whole galaxy," asks Harrison.

By studying the x-rays being emitted by the quasar, Harrison and colleagues found there was a persistent, almost spherical stream of very powerful, highly ionized gas flowing out from the black hole and into the rest of the galaxy.

"This wind is coming off at all angles, pumping enough power into the galaxy to rival the power in star formation and influence the energetics of this galaxy so this is a connection between the black hole and the galaxy."

These winds, which astronomers have named Ultra Fast Out flows or UFOs, are strong enough to disrupt molecular gas and dust clouds, preventing them from collapsing to form new stars.

"This new measurement tells us that not only is this material flowing out incredibly fast, at a significant fraction of the speed of light, but it's also very powerful, which is something we've previously only been able to speculate about," says Harrison.

Two telescopes are better than one

According to Harrison, combining the data from two X-ray telescopes was key to understanding the importance of these black hole winds in galactic evolution.

XMM-Newton was able to observe lower-energy X-rays caused by iron atoms being carried along by these winds, however it couldn't tell how wide or narrow the beams were.

By adding higher energy X-ray wavelengths observed by NuSTAR, Harrison and colleagues were able to determine that the energy emitted by the quasar wasn't just a narrow jet, but formed a far wider beam emanating in all directions.