Rapid Changes Point to Origin of Ultra-fast Black Hole Winds

Astronomers have made the most detailed observation yet of an ultra-fast wind emanating from a Black Hole at a quarter of the speed of light. Using the European Space Agency (ESA)’s XMM-Newton and NASA’s NuSTAR telescopes, the scientists observed the phenomenon in an active galaxy known as IRAS 13224-3809.

black hole
Artist's impression of the winds emanating from the supermassive black hole Credit: European Space Agency (ESA)

Understanding these winds is crucial to understanding how galaxies, including our own, grow

Dr Michael Parker

Outflowing gas is a common features of the supermassive black holes that reside at the centre of large galaxies. Often millions of times more massive than the Sun, these black holes feed off the surrounding gas that swirls around them. Space telescopes observe this as a bright light from the innermost part of the disc around the black hole.

Occasionally the black holes consume too much gas and release an ultra-fast wind. These winds are an important characteristic to study because they could have a strong influence on regulating the growth of the host galaxy by clearing the surrounding gas away and therefore suppressing the birth of stars.

Using ESA’s XMM-Newton and NASA’s NuStar telescopes, scientists have now made the most detailed observation yet of such an outflow. The winds recorded from the black hole reach 71,000 km/s – a quarter of the speed of light – putting it in the top 5% of fastest known black hole winds.

XMM-Newton focused on the black hole for 17 consecutive days, revealing the extremely variable nature of the winds.

“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,” says Dr Michael Parker of the Institute of Astronomy at the University of Cambridge, UK, lead author on a paper published in Nature this week which describes the discovery.

“Thanks to this long observation campaign, we observed changes in the winds on a timescale of less than an hour for the first time.”

The changes were seen in the increasing temperature of the winds, a signature of their response to greater X-ray emission from the disc right next to the black hole.

Furthermore, the observations also revealed changes to the chemical fingerprints of the outflowing gas: as the X-ray emission increased, it stripped electrons in the wind from their atoms, erasing the wind signatures seen in the data.

“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,” says co-author Professor Andrew Fabian, also from the Institute of Astronomy, and principal investigator on the project.

“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.”

Dr Parker adds: “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.”