Ultra-fast winds explain galaxy growth

Scientists at the University of Cambridge have captured the most detailed measurements of gases flowing from black holes, helping them better understand galaxy growth.

At the centre of large galaxies, supermassive black holes feed off the gas that surrounds them. Occasionally they consume too much gas and release ultra-fast winds. The researchers believe these winds clear away surrounding gas, preventing the birth of stars.

Dr Michael Parker, from the University of Cambridge and lead author of the study, said: “Black hole winds are one of the mechanisms for feedback, where the energy coming out from the black hole regulates the growth of the host galaxy. Understanding these winds is crucial to understanding how galaxies, including our own, grow.”

Using the European Space Agency (ESA)’s XMM-Newton and NASA’s NuSTAR telescopes, the scientists observed galaxy IRAS 13224-3809. XMM-Newton focused on the black hole for 17 consecutive days and recorded winds reaching speeds of 71,000 km/s – a quarter of the speed of light. This places them in the top 5% of fastest known black hole winds.

Dr Parker said: “We often only have one observation of a particular object, then several months or even years later we observe it again and see if there’s been a change. Thanks to this long observation campaign, we observed changes in the winds on a timescale of less than an hour for the first time.”

These changes included increasing temperatures of the winds, due to increased X-ray emission from the innermost disc around the black hole. These emissions also stripped electrons in the wind from atoms, erasing the wind signatures observed.

Professor Andrew Fabian, also from the University of Cambridge said: “The chemical fingerprints of the wind changed with the strength of the X-rays in less than an hour, hundreds of times faster than ever seen before. It allows us to link the X-ray emission arising from the material falling into the black hole, to the variability of the outflowing wind farther away.”

The research was published in Nature.